Exposure to

PRACTICAL IN POWER DISTRIBUTION General Tools

Electrical power is essential for economic development and for improving

the quality of life. The three major parts of electrical power system are
generation, transmission and distribution. You are primarily dealing with
the distribution part of the electrical system, i.e. the part that brings
electrical power to the consumer.

This course provides you with the requisite knowledge to enable you to be
well informed and capable of working with the electrical system with
complete understanding. However, we realize that only theory subject is
not sufficient to make you confident in your day-to-day working life. This
practical workbook is to help you on this count. We recognize that practice
work is required to give you that hands-on experience, which will make
you confident and also make you aware of the problems, which you may
face in your day-to-day work-life. This practical workbook is to aid
fulfillment of this aim.

This course is laid out in ‘activities’, whereby each activity takes up one
task connected with the act of providing electrical power to the retail
customer. These tasks have been chosen, as these are the activities most
likely to be faced by you, in your working life.

Each ‘activity’ describes the task taken up therein, and provides some
background or theoretical information for proper understanding and
appreciation of the activity. The required tool and tackle are described,
and only then is the task started. The practical course is designed to be a
guide to the practical activity, to be carried out in the presence of, and
under the guidance of an experience trainer.

In these activities we introduce technical dimension of the power

distribution system and discuss its operation and maintenance aspects
also. It is our belief that significant improvement can be brought about in
the power sector just by toning up the operational and maintenance
practices, sharpening of work culture and training.

We hope that the activities presented here related to power distribution,

would provide you an insight into the working of the sector and help you in
carrying out your responsibilities better.

At the end of the practical workbook, you are expected to be reasonably

proficient in practically handling the stated activities.

Happy learning & Wish you all the very best.

39
Electrical

40
 Indira Gandhi
National Open University
School of Engineering and Technology
OEEL-001
PRACTICAL IN
POWER DISTRIBUTION

Content
s
PRACTICAL IN POWER DISTRIBUTION
Activity 1
Digging Holes and Erection of Poles 5

Activity 2
Fixing Different Fittings on Poles 13

Activity 3
Stringing and Sagging in Overhead Line Conductors 19

Activity 4
Jointing Overhead Line Conductors 27

Activity 5
Installation of Overhead Service Lines 33

Activity 6
Identification of Cable Jointing Kits and Terminations 37

Activity 7
Measuring the Earth Resistance 47

Activity 8
Inspection and Routine Maintenance of a Transformer 53

Activity 9
Troubleshooting and Maintenance of Switchgears 61

Activity 10
Installation and Sealing of Energy Meters 71

Activity 11
Testing of Domestic Wiring Installations 83

Activity 12
Various Faults in House Wiring and their Rectification 89
 Practical in
Activity No. 1 Power Distribution

PRACTICE FOR DIGGING HOLES AND ERECTION

OF POLES

Structure
1.1 Objectives of Activity
1.2 Equipment/Materials/Facilities Required
1.3 Brief Theory
1.4 Procedure
1.5 Tabular Record of Observations
1.6 Precautions
1.7 Self Test

1.1 Objectives of Activity

 After performing this activity, you should be able to

 practice the technique for the erection of poles for

overhead lines.

 describe the safety measures to be taken during

erection of poles.

 understand economical and accident-free utilization

of labour during erection.

1.2 Equipment/Materials/Facilities Required

 Drilling Machine.

 Earth auger (i.e. to drill a hole in earth), digging bars, shovels

or pick axes.

 Three ropes of ¾ ” diameter each and one rope of 1¼ ”

diameter, and nearly 40 ft. to 50 ft. long.

 X-shape wooden frame for supporting the pole while erecting,

 Hoisting rig, a trunk or a skid winch, or a derrick pole.

 Standard tools.

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Practical in
Power Distribution
1.3 Brief Theory

After a route survey of the transmission line , the poles have to be

erected, so that further action of stringing and sagging of the conductors
may be undertaken.

1.4 Procedure

(1) Transportation of Poles

All other material can be transported easily either in a truck or a

bullock cart. For poles, (though this can also be done by the above
mentioned methods) it is recommended that a special trolley be
made and which may be pulled either by bullocks or a tractor or by
manual labour. After the poles are transported, erection work starts.

(2) Preparation of the Poles for Erection

After the poles have reached the site, the following operations
should be completed.

 Drill the Holes

 Paint the pole, if not already done. (Not needed in the

case of concrete poles.)

 Fit the cross-arm and knee bracing

 Fix up pins and clamps for insulators

 If muffs are provided, they should be grouted on the

poles. If not, grouting should be done later on.

(3) Digging of Holes

After fixing the point where the pole is to be erected, a hole is to be

excavated in the ground. The depth to which the pole is to be
planted is a matter, which can only be determined in the light of past
experience. Roughly 1/6th of the length of the pole is planted. In the
case of planting in solid rocks, the depth is less.

The following table shall be a useful reference in digging holes in the

ground.
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 Practical in
Length of Pole Depth in Ground Depth in Power Distribution
(Ft.) in Solid Earth Ground in Solid
(Ft.) Rock (Ft.)

25´ – 0" 5´ – 0" 3´ – 6"

30´ – 0" 5´ – 0" 3´ – 6"

36´ – 0" 6´ – 0" 4´ – 0"

42´ – 0" 7´ – 0" 4´ – 6"

65´ – 70’ 8´ – 0" 6´ – 0"

 Size at the Top and at the Bottom

It should be sufficiently larger than the pole (or pole base, if
used) to allow the use of tempering bars for tamping. In
ordinary firm soil, pole holes are excavated by :

 Hand, using digging bars, shovels or pickaxes,

 Earth augers, and

 Drilling machine.

If the hole is dug manually it should be 3´  1½ ´ in size and

should be tapered. If it is dug by an earth auger or drilling rig, it
should be 9 or 10 inch diameter, depending on the size of the
pole.

The hole should be in the same position as the intended

position of the pole at the bottom.

A concrete pad of 3´ thickness may be prepared at the bottom

to provide a firm base.

(4) Raising of Poles

Three ropes of 3/4" diameter and one of 1¼ " diameter, 40 to 50 feet

long are tied near the top of the pole, with pole in the horizontal
position.

Then the pole is raised by about 5 to 6 feet on a wooden X-shaped

frame. One or two men, depending upon the weight of the pole,
should hold the 3/4" ropes in three different directions and 3 to
4 men should hold the 1¼ " rope in the fourth direction. Then the
pole may be pulled by these men till it gets into the pit. A hoisting rig,
a trunk or a skid winch can be used with advantage. A derrick pole
can also be used with advantage. This pole being lighter, is first
7
Practical in
erected, and then, by pulling the pole which is to be erected, the
Power Distribution
derrick pole is lowered.

It becomes easy to lift the pole.

Figure 1.1 : Derrick Pole Method

(5) Checking of Pole Alignment

As soon as the pole is erected, it should also be checked for

verticality by a plumb – bob.

(6) Concreting the Pole

Poles should have a strong foundation, because the failure of the

pole may not necessarily be due to a crack or fracture, but due to
wrong foundation. If the muff is pre-cast, this is to be fitted before
the erection of the pole. Then only the earth is to be tamped. It is
better to tamp in more soil than comes out of the original hole to
provide greater firmness. If the pole has not been fitted by a pre-cast
muff, then it should be grouted by cement concrete mixture in the
ratio of 1 : 2 : 4.

If the hole is drilled by means of an earth auger or drilling rig then it

should be grouted without the aid of a steel muff but if a larger hole
has been dug, then a steel plate muff of 10" diameter, or another
suitable size, depending upon the size of the pole may be used.

This steel muff may be removed the after one day of the installation.
The baulk should be one foot above grounded level. It is essential
that this casing should be beveled at the top to prevent lodgment of
water between the concrete and the pole surface.

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 Practical in
1.5 Tabular Record of Observations Power Distribution

After erection of poles, record observations in the following tabular form

(the data pre-filled in the ‘Data’ column is to serve as an example, and
should be replaced with the actual values).

Sl. Details Data Pole Pole Pole

No. No. 1 No. 2 No. 3

1. Length of pole 30 ft.

2. Type of pole, whether Steel

PCC/steel

3. Height above ground 25 ft

4. Depth in ground 5 ft.

5. Whether muff is provided or Yes

not

6. Type of X-arm Horizontal

7. Whether angle pole or not No

8. Nos. of holes drilled 5 Nos.

9. Paint done or not Done

POLE

500 500 TOP BAULK

NUT WASHER

100  200  1200

(BAULK)
2 BOTTOM
BAULK

300
(a) For Normal Soil (b) For Loose Soil

All Dimensions are in mm

Figure 1.2 : Fitting Baulk in Foundation of Pole

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Practical in
Power Distribution
1.6 Precautions

 Ropes should be of the proper size.

 Muffing should be provided as necessary.

 One coat of paint, together with anti-rust treatment, must be

done on steel poles.

 Proper numbering must be put on the poles

 Record of data regarding each pole must be prepared carefully.

 Holes must be dig to the proper depth

 Take safety measures to avoid accidents.

 To have proper coordination and economical utilization of

manpower, one person from the gang of erectors must be
made leader, so that others work under his command.

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 Practical in
Power Distribution
Self Test Answer the following questions :

Q.1 What procedure is used for erection of overhead line pole? Also
draw a diagram for showing the erection of the pole.

Q.2 Why muffing is necessary?

Q.3 Give the necessity of paint on steel poles.

Q.4 Why alignment of the pole is necessary?

Q.5 Why proper coordination is required in the gang of erectors?

11
Practical in
Power Distribution

12
 Practical in
Activity No. 2 Power Distribution

PRACTICE OF FIXING DIFFERENT FITTINGS ON

POLES SUCH AS CROSS-ARMS, INSULATORS,
STAY-WIRE, GUY RODS/WIRES

Structure
2.1 Objectives of Activity
2.2 Equipment/Materials/Facilities Required
2.3 Brief Theory
2.4 Procedure
2.5 Tabular Record of Observations
2.6 Precautions
2.7 Self Test

2.1 Objectives of Activity

 After performing this activity, you should be able to

 get familiar with different kinds of fixtures/fittings are

in use for overhead lines.

 know about the fixing of these fittings on poles.

 make economical utilization of manpower and

materials.

2.2 Equipment/Materials/Facilities Required

 Cross-arms

 Insulators with fittings

 Anchor rods

 Stay wires

 Guy rods/wires

 Stay insulators

 Overhead conductors

 Conductor clamps

 Line construction tool kit.

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Practical in
Power Distribution
2.3 Brief Theory

The main function of a pole is to support conductors at a safe distance

above the ground. Multiple conductors must also be kept a safe distance
apart from each other. This is the function of the cross-arm. Several
designs are in use. They vary from a steel channel to V, U and zig-zag
shape or teak wood or sheesham wood cross-arm. In order to prevent
arcing, the construction should be such that under the worst conditions,
the distance between wires, when swinging, will never be less than the
following figures, anywhere along the length :

Line Voltage Separation

3.3 kV 7.5 cm
6.6 kV 7.5 cm
11 kV 10 cm
33 kV 10 cm

A guy is a brace or stranded wire fastened to the pole to strengthen

the pole and to keep it in position. Guys provide ‘pull’ support. Guys are
used wherever the wires tend to pull the pole out of its normal position
and to sustain the line during the abnormal loads caused by sleet, wind
and cold. Guys may be classified as braces; wire guys; anchor or down
guy and stub guy.

Braces are used wherever wire guying is not convenient such as

along lines paralleling a highway or in marshes where anchors cannot be
firmly embedded. A span guy is a wire guy running from the top of a pole
to the top of an adjacent pole. It is used at important crossing.

A head guy is a wire running from one side of a cross-man to the

next pole. An anchor or down guy is a wire guy running from the top
of a pole to an anchor in the ground. Line guys are installed in straight
pole lines to reinforce the line against stresses due to broken conductors,
etc. Side guys are used to reinforce a pole line against an unbalanced
side pull of the conductors. Such pulls are developed at curves, angles,
wherever there is a turn in the line.

A storms guy is a combination of line and side guys. A stub guy is a

means of obtaining clearance for a wire guy. A sidewalk guy is an anchor
guy with a horizontal strut at a height above a sidewalk to clear the walk.

A wire guy consists of a cable, cable clamps, strain insulator and anchor.
The function of an insulator and anchor : The function of an insulator
pin is to hold the insulator mounted on it in a vertical position. Insulator
14
 Practical in
pins holds the insulator mounted on it in a vertical position. Insulator pins Power Distribution
in use in the field are made of metal e.g. iron or steel. The function of an
insulator is to insulate the line conductors from each other and from the
pole or tower.

Three classes of insulators are used on overhead lines, namely, pin

type, suspension type and strain type.

The pin insulator gets its name from the fact that it is supported on a pin.
The pin holds the insulator, and the insulator has the conductor tied to it.
Pin insulator commonly in use these days, are made of porcelain.

The suspension insulator as its name implies, is supported from the

cross-arm and has the line conductor fastened to its lower end. It is made
up of a number of sections stringed together. These are mainly used for
high voltages above 33 kV. At this voltage, the pin insulator becomes
quite heavy and it is difficult to obtain sufficient mechanical strength in the
pin to support the insulator.

The use of a suspension insulator eliminates the use of the pin and
makes it possible to obtain any distance between the conductors and the
pole or tower by merely increasing the number of insulators in the string.

A strain insulator is used where a pull must be carried as well as

insulation provided. Such places occur where a line is dead ended, at
corners, at sharp curves, at extra long spans, as at river crossings or
mountainous country, etc. in such places the insulator insulates
electrically, but must also have sufficient mechanical strength to
counterbalance the forces due to tension in the line conductors.

2.4 Procedure

(i) Complete drilling of holes for the cross-arm and guy support,
before shifting the poles to the site for erection.

(ii) Decide the length of cross-arm to be used and use a template

for boring holes. For 11 kV lines, the length of the cross-arm
is nearly 5´-0" but for special requirements a length of 7´-0"
and 10´-0" may also be used. For a 33 kV line a 7´-0" long
cross-arm and knee bracings should be at right angles to
each other.

(iii) Use H-pole where unusual loads have to be withstood – at

angles or at line terminal corners, or at branch lines, etc. 15
Practical in
Power Distribution
alternatively, single poles supported by wire guys or pole
struts can be employed.

(iv) Installation of a guy involves the following operations :

digging-in the anchor, inserting the strain insulator in the guy
wire, fastening the guy wire to the pole; tightening the guy
wire and fastening to the anchor, and mounting the guy wire
guard. Guy wires should be placed on the poled and stay rod
fixed before the line conductors are stretched on the poles. If
line conductor are placed first, the poles would be pulled out
of position. The guy-wire tightening may need to be re-done
after the line conductors are stretched.

(v) Insert an egg type strain insulator for safety. The two ends of
guys should be threaded through the insulator in such a way
that the porcelain of the insulator is under compression,
making it possible to withstand a larger pull. In case the
porcelain breaks, the guy will still be effective because of the
linking of the two ends.

(vi) Draw the guy up until the pole is pulled over slightly towards
the guy to keep proper tension.

Error!
750
D

80
A 80

B C 200

E 400

SHACKLE-INSULATOR
PIN
INSULATOR

STEEL BRACING

250

POLE

All Dimensions are in mm

Figure 2.1 : Different Fittings on Poles

16
 Practical in
2.5 Tabular Record of Observations Power Distribution

The trainer should ask the technicians to do on the spot erection and then
tell them to prepare a diary report. They should prepare pole-wise details
of the fittings provided.
If some fixture is not provided, then ‘no’ should be mentioned in the table.

Tabular Record of Observations

Sl. No. Fittings Pole Pole Pole Pole

No. 1 No. 2 No. 3 No. 4

1. Cross-arm Yes

2. Guy wire Yes

3. Knee bracing Yes

4. Pole clamps Yes

5. Guy insulator Yes

6. Thimble Yes

7. Stay rod Yes

8. Lock nut Yes

9. Stay bow Yes

2.6 Precautions

 Holes of cross-arms and knee bracings should be at right

angles to each other

 Guy wires should be placed on the poles and the stay rod must
be fixed before the line conductors are stretched on the poles

 Thimbles should be used at both ends of the guy to avoid

damage to strands

 Use strain insulators for safety.

17
Practical in
Power Distribution Answer the following questions :
Self Test

Q.1 Write short note on the following :

(a) Guy

(b) Anchor

(c) Cross-arms

Q.2 Why thimbles are used at the ends of guy wire?

Q.3 What is the use of egg types strain insulator?

Q.4 Define insulator and give classification of overhead line insulators?

18
 Practical in
Activity No. 3 Power Distribution

PRACTICE OF STRIGING AND SAGGING IN

OVERHEAD LINE CONDUCTORS

Structure
3.1 Objectives of Activity
3.2 Equipment/Materials/Facilities Required
3.3 Brief Theory
3.4 Procedure
3.5 Tabular Record of Observations
3.6 Precautions
3.7 Self Test

3.1 Objectives of Activity

 After performing this activity, you should be able to

 get familiar with the techniques to reel out the

conductor, and string it for sagging in overhead line
construction.
 know sagging and tying of the line conductor.
 acquaint the technicians with a systematic procedure
for overhead line erection.

3.2 Equipment/Materials/Facilities Required

 Erected poles with fittings
 Line conductor
 Pulling blocks
 Snatch block
 Ropes
 Tie Wires
 Vehicle for carriage
 Light strips of wood to serve as targets
 Come-along or pulling grips
 Block and tackle or chain block
 Lineman hand tools

 Safety belt 19
Practical in
Power Distribution
3.3 Brief Theory

After the poles have been erected and fixtures set on the poles, the most
important phase of line construction starts, which is stringing and sagging
the line conductor, stringing it so that the overhead line is erected as per
specifications. The final phase of tying-in is also needed before the line is
ready.

 Reeling Out of the Conductors

Reeling out of the conductors may be accomplished by either of the
two methods :

Methods for reeling out of conductors

1. Moving reels with the conductor stationary.

2. Pulling conductors from stationary reels.

The first method involves the following steps :

(1) Mount the reels of wire (as many reels as the number of
conductors to be strung) on a truck or carriage in such a
manner that the reels are free to rotate.

(2) Fasten the ends of the conductors to a pole, tower footing

or some other fixed object.

(3) Drive the truck slowly along the route of the line, allowing
the conductors to unwind as the reels are moved forward.
Care should be taken to avoid inter-twining of the
conductors while unreeling.

By this method the conductors are not dragged over the

ground, avoiding scratching or damage. They are simply laid
out on the ground without being pulled over it.

The second method involves the following steps :

(1) As the reels on which conductors are wound remain in a

fixed position, these are raised off the ground or
supported in their carriages in such a way that they are
free to rotate.

(2) Pull out conductors, thereby, rotating the reels and

unwinding the conductors.

20
 Practical in
(3) Either simply draw the conductors forward, sliding or Power Distribution
dragging them over the ground or keep these suspended
in the air in tension so that they will not touch the ground.
Take care that the conductors do not get scratches, as it
will not only damage the conductor, but later lead to
corona loss. For aluminum conductors in use these days,
‘suspension in the air’ method is better.

 Stringing and Hoisting Line – Conductors

It is a common practice to use the tension stringing method for

overhead lines. Tension stringing is the process in which conductors
are kept off the ground throughout the entire stringing operation.

To keep the conductors in tension, a puller is required on the leading

end of the conductor and a brake or tension on the trailing end of the
conductor.

Before the stringing operation is begun a pulling line of wire rope for
transmission lines or manila rope for distribution lines is attached to
the leading end of the conductor and is run through stringing
sheaves hung from each tower or pole cross-arm for the full distance
from the tensioner to the puller. It is the function of the pulling line to
pull the conductor into the stringing sheaves, as it is pulled forward
by the puller.

As the conductors are reeled out, they are hoisted up to the

cross-arm. Each time a pole or tower is reached, the truck or tractor
pulling the conductor, pulls a little ahead and halts to permit each
wire or cable to be hoisted. This is generally done by means of a
hand line.

Hoisting of the conductor to the cross-arm is called Laying up. The

common practice is to use snatch blocks for ‘Laying up’, or rope
baskets in city areas, where it is not possible to switch off supply all
the time. In this way, instead of placing conductors directly on the
cross-arm which may damage the conductors due to scratches,
conductors are hung in so called snatch blocks.

A snatch block is a single sheave block so arranged that it opens in

one side, thereby, permitting the conductor to be inserted or
removed without threading it through.
21
Practical in
A snatch block serves two purposes :
Power Distribution
 It is a support for the line conductor.

 The pulley on the block runs so easily that it aids the

conductor in taking on a uniform tension throughout,
attaching to the suspension insulator. Rope baskets
consist of two parallel ropes support from the ends of the
cross-arms in the crossing span with numerous cross
ropes to cater or support the unstrung conductors.

 Pulling up of Conductor

After the conductors are hoisted, they are ready to be pulled up. To
carry out this operation a come-along, or pulling grip is fastened to
the end of the line conductor. There are several makes of
come-along in general use. All are designed with parallel jaws that
will grip the wire firmly without injuring it. The conductors may be
pulled from the top of the pole in the case of short line extension.

The pole used to pull from, must be properly guyed to withstand the
strain. If there is quite a bit of pulling to be done, however, as in new
construction, it is better, easier and faster to pull from the ground
than on the pole.

After the conductors are pulled to the proper tension or sag, the
conductors can be snubbed to the bottom of the pole to which the
block and tackle is attached. Care should be taken in pulling up, so
that splices and sleeves do not catch on the cross-arm or in the
sleeves of snatch blocks. Any catch of this sort may prevent the
conductor from coming up as it should.

After the conductors are pulled, they should have ½ to 4 hours or

more depending upon the length of the pull, to allow them to creep.
This creep will make the tension and sag in each span uniform.

When possible, an equalizer may be used in pulling up conductors in

order to produce the same tension on each conductor. A simple form
of equalizer for two conductors consists of a rope with a come-along
on each end to grip the two line wires. The rope runs over a snatch
block to which the pulling tackle is attached. Since the rope is free to
move through the snatch block, the conductors will pull up to the
same tension.
22
 Practical in
 Sagging the Conductor Power Distribution

Conductors are sagged uniformly when the tension is the same in

each span throughout the entire length. New conductors must be
pre-stretched so as to remove the non-elastic stretch.

Several different methods are used : Sighting, use of transit,

timing waves and use of a dynamometer.

In usual practice, only sighting and use of transit is followed.

In sighting for sag, it is better to select a span near the middle of the
length pulled up. The length of wire pulled at one time may vary from
a few hundred feet to a half-mile (around 800 m) or more.
Preferably, a span near the middle of the length pulled should,
therefore, be selected in sighting for sag. If the section includes a
number of curves, it is desirable to sag at more than one point.

A simple and accurate method of measuring the sag is by the

use of targets placed on the poles below the cross-arm. The
targets may be a light strip of wood like a lath nailed to the pole, at a
distance below the conductor when resting on the insulator equal to
the desired sag. The lineman sights from one lath to the next. The
tension on the conductor is then reduced or increased until the
lowest part of the conductor in the span coincides with the lineman’s
line of sight. Sagging T’s can also be used in the same way as the
targets, except that T’s are hung on the line conductor.

In the case of an H-frame line, where the line conductors are on one
or the other sides of the poles, a lineman stationed on one pole and
looking at a corresponding pole span-length away, cannot include
the lowest point of the conductor in his line of sight.

To get around this difficulty, a transit is securely fastened to the pole

at distance equal to the desired sag, below the conductor support.
Then the transit is leveled.

To observe the sag, the transit is sighted at the conductor at

mid-span and then is swung around until it is in line with the pole a
span length away. The conductor is drawn up farther if the sag is too
large or relaxed if the sag is too small.

 Releasing Pulling Blocks

After the conductors are pulled up, provide a temporary dead end to
hold the conductor until the next stretch of wire is pulled up and held.
23
Practical in
A temporary dead end can be arranged by running a head guy from
Power Distribution
the top of the last pole ‘a’ to the butt of next pole ‘b’.

A lineman then climbs pole ‘a’ and hitches a come-along to the

cross-arm by means of a rope sling and then reaches out and slides
the come-along along the wire as far as possible so that the grip will
hold the wire when the pulling blocks are released. After
dead-ending or snubbing is completed, the pulling blocks should be
gradually released. Avoid releasing with a jerk, or an abnormal
stress may be placed on the conductor and their supports, which
might result in failure such as the snapping of a pin, cross-arm guy,
or even a pole, in extreme cases.

Tying in

Conductors should occupy such a position on the insulator as

will produce minimum strain on the tie wire. The function of the
tie wire is only to hold the conductor in place on the insulator,
leaving the insulator and pin to take the strain of the conductor.

The common practice is to use wire ties throughout in the

distribution system and almost entirely on the transmission
lines, when pin insulators are employed. For suspension
insulators, clamps are used. Different kinds of ties are in use.

The point is that it should be easy to apply and relatively simple

to make, keeping in mind its function, that it should bind the
line conductor securely to the insulator and, in addition, should
reinforce the conductor on the both sides of the insulator.
However, the tie wire should be of the same kind of wire as the
line wire. Never use a tie wire a second time.

3.4 Procedure
(i) After the poles have been erected and fixtures have been set
on the poles, reel out and stretch the conductor along the line
using any method described earlier, depending upon the
availability of equipment. If a truck or carriage is available, then
use the method of moving the reels with the conductor
stationary. In our countryside, for small rural area lines, the
practice adopted is to take conductors in bundles to the site of
work after reeling them out manually in the stores and then to
stretch them manually.

24
 Practical in
(ii) Use tension stringing and hoist the line conductors on the
Power Distribution
cross-arm. Use snatch blocks instead of laying up directly on
cross-arms.
(iii) Perform puling-up operation for line conductors using
come-along or pulling grip, block and tackle or chain block as
per availability. To produce the same tension in line
conductors, use an equalizer.
(iv) Perform the sagging operation, using sighting method in
general and transit method, wherever an H-pole frame is used.
(v) After sagging is done, release pulling blocks.

(vi) Perform tying-in operation at every pole using tie wires nearly
3 ft. long.

3.5 Tabular Record of Observations

The following measurement should be recorded for all material used as

per example below :

Sl. No. Item Quantity

1. Poles 10 Nos.

2. Aluminium conductor 3000 m.

3. Cross-arms 10 Nos.

3.6 Precautions
 Avoid scratching of the conductor by its coming in touch with
the ground as it may damage or injure the line conductors.
 Sagging should be done with equal tension in all the line
conductors.
 The tie wire should be for the same material as the line wire.

 Release the pulling blocks slowly and not with a jerk as that will
put abnormal stresses on the conductors and supports which
may lead to failure, such as snapping of pins.

 The measurement record of the material used on the line must

be completed.

 Conductors must not be allowed to lay up on steel cross-arm

as there may be damage to the conductors.

25
Practical in
Power Distribution Answer the following questions :
Self Test

Q.1 Write the importance of stringing and sagging?

Q.2 Explain the methods for reeling out of the conductors.

Q.3 Why damage on the surface of conductor is avoided?

Q.4 What is the result of unequal tension in the line conductors?

Q.5 Draw a diagram showing the sagging of conductors of any line.

26
 Practical in
Activity No. 4 Power Distribution

PRACTICE OF JOINTING OVERHEAD LINE

CONDUCTORS

Structure
4.1 Objectives of Activity
4.2 Brief Theory
4.3 Equipment/Materials/Facilities Required
4.4 Procedure
4.5 Precautions
4.6 Self Test

4.1 Objectives of Activity

 After performing this activity, you should be able to

 get familiar with different types of line joints and

practice of joining line conductors, and

 acquire knowledge regarding, which type of joint is

to be used under which situation.

4.2 Brief Theory

Joining conductors is a practical requirement. It may be required while

laying a new power line, because the conductor length on a reel may be
insufficient to span the total length of the line. Even for an existing line, a
break in the conductor may have to be repaired by joining.

Line joints can be divided into three classes : splices, sleeve joints and
compression joints. Splicing is suitable for small-sized copper conductors.
But, larger sizes of hard drawn copper and aluminum conductors are
usually joined by means of splicing sleeves or compression joints. There
is another class of splicing, called Automatic Splice. This class is not
included here.

In the field, the common practice is to use sleeve joints and compression
joints to join overhead line conductors.

4.3 Equipment/Facilities /Materials Required

 Line conductors
 Splicing clamps (connectors) 27
Practical in  Cleaning material
Power Distribution
 Pliers
 Sleeves twisters
 Compression die
 Sleeves

 Friction tape

4.4 Procedure
 Making a Splice
(i) Scrape the two end sections of the conductors to be spliced
and clean with cleanser. The conductors should be cleaned
until bright. Remove all rough or high spots.

(ii) Place the cleaned conductors together until approximately 20

to 30 cm (for smaller sizes)/30 to 40 cm (for larger sizes) of the
ends overlap each other.

(iii) Place splicing clamps (known as connectors) on the two

conductors about 10 cm from the end of the conductor. See
that the connectors grip both the conductor firmly. The
conductors should not be allowed to slip or turn in the
connectors, otherwise a ‘burned’ conductor will result and one
of the conductors will eventually break at that point.

(iv) Twist conductors from both ends i.e. wrap each conductor
about the other conductor. The usual number of turns to be
made is four. More turns may burn the conductor while less
may give away and the conductors will crawl apart.

(v) Shift both connectors on to the twisted portion of the

conductors. The shift required will be equal to the width of the
connector.

(vi) With a pair of pliers, finish the splice by serving up the ends.
Finishing is done by wrapping the loose ends of the wire about
the conductors. Three or four turns are the usual number.
These turns are known as ‘buttons’.

(vii) After the buttons are on, the ends should be cut close to the
splice.

(viii) Solder the Splice.

(ix) Wrap the open section with four layers of friction tape and paint
with compound if covered wires are used.
28
 Practical in
 Marking a Sleeve Joint Power Distribution

Medium-size line conductors are best joined by a splicing sleeve,

which is a special connection to ensure good electrical and
mechanical joints. The sleeve itself is a piece of single or double
tubing. To make a sleeve joint, the procedure is as follows :

(i) Scrape both end sections of the wires clean and bright.

(ii) Run wires through sleeves, allowing the ends to protrude,

i.e. the ends of the wires should project about 10-5 cm
beyond the ends of the sleeve.

(iii) Bend these wires with pliers. This bending keeps them
from slipping out of the sleeve.

(iv) Make three and a half turns with sleeve twisters, one on
either end. Twist lightly.

(v) Cut off the excess conductor beyond the joint on either
side and the joint is completed.

(vi) Sleeves should be made of the same kind of material as

the line conductor.

 Making a Compression Joint

Compression joint also makes use of a sleeve. Instead of twisting
the sleeve, however, the sleeve is compressed with great force onto
the conductor. The use of a die in compression makes the sleeve
grip the conductors firmly.

The orders of steps for making a compression joint are as

below :

(i) Clean conductor end sections thoroughly. All dirt and

grease should be removed with gasoline or similar
cleaning solvent. When a conductor that has been in
series, is being spliced, special care should be taken to
remove oxidation on that portion which is inserted in the
sleeve.

(ii) Match the size of splicing sleeve to the size of the

conductor.

(iii) The die number must be matched to the sleeve number.

(iv) The conductor ends must be properly centered in the

sleeve. 29
Practical in
(v) The specified number of indents must be made.
Power Distribution

(vi) The joint is ready.

4.5 Precautions

 The ends of the wires must be cleaned until they are bright.
Any rough or high spots must be removed.

 Connectors should grip the ends of the conductors properly.

 Only the require number of turns should be used in twisting.

 Shift of connectors should be equal to the width of the

connector.

 Finishing should be done carefully using pliers.

30
 Practical in
Power Distribution
Self Test Answer the following questions :

Q.1 Describe the process of joining line conductors.

Q.2 Describe the specific safety precautions taken during jointing

overhead line conductors.

Q.3 Discuss the common practices used for joining overhead line
conductors.

Q.4 Write various steps for making a compression joint.

Q.5 Excessive twisting of the conductors is not good, why?

31
Practical in
Power Distribution

32
 Practical in
Activity No. 5 Power Distribution

PRACTICE OF INSTALLATION OF OVERHEAD

SERVICE LINE

Structure
5.1 Objectives of Activity
5.2 Equipment/Materials/Facilities Required
5.3 Brief Theory
5.4 Procedure
5.5 Log Book
5.6 Self Test

5.1 Objectives of Activity

 After performing this activity, you should be able to

 install the over head service line for a single storey

building.

5.2 Equipment/Facilities/Material Required

 Equipment/Tools
Lineman’s Tool Kit, Lineman’s Personal Protective Equipments.

 Facilities
LT Overhead line, Single storey structure where service line is
required to be installed.

 Material Required
Sl. Material Quantity Remarks
No.
1. GI Wire Length from pole to
house + 10% extra
2. I Thimble 1 No.
3. Pole Clamp 1 No.
4. Pipe Clamp 2 Nos.
5. 50 mm G I Pipe 3m
6. Ring Insulators 4 Nos. per meter
7. Stay Wire 7/10 3m
8. Stay bows 2 Nos.
9. Stay rod with bolts 1 No.
33
Practical in 10. Stay Insulator 1 No.
Power Distribution
11. IC 30 cm x 25 cm 1 No.
main board
12. I C Kit Kat 10 Amps 1 No.
13. Neutral link 1 No.
14. Single core weather Length x 2 plus 10%
proof wire extra length up to
main board
15. Cement and River Lot
Sand
16. GI Wire No.14 ½ kg
17. Shackle Insulators 4 Nos. (250 V)

5.3 Brief Theory

In case the consumer’s premise is less than 45 metres away from the
nearest distribution line, the service connection may be provided by
means of overhead weather proof or PVC cable.

Aerial Fuse

E
L
Stay Wire
M G.I. Pipe
Rest
Insulator
Shackle
Insulator

Meter
Board

Figure 5.1 : Overhead Service Line for Single Storey Building

5.4 Procedure

(i) Tie the ring insulator with GI Wire No 14.

(ii) Fix the pole clamp on pole with the Shackle insulators and
I-hook.

(iii) Fix the G.I. pipe of 50 mm size with bend on the house wall
near the main board.

(iv) Fix the stay wire.

34
 (v) Fix the pipe clamp with I-hook and shackle insulators as shown Practical in
Power Distribution
in Figure 5.1.
(vi) Insert the wires (G.I. + weather proof) in the ring insulators. The
ring insulators must be equally spaced along the length of the
GI wire.
(vii) Tie the G.I. wire with I-hooks at the pole and pipe.
(viii) Take tapping from the weather-proof wires for main board.
(ix) Insert the tapped wire in the G. I. pipe.
(x) Make connections on the main board by fixing neutral link, fuse
Kit Kat.
(xi) Fix the energy meter and give connection.

(xii) Give connection at the pole to the main overhead line subject
to safety precautions, in case of live main line.

G. I. Pipe
G. I. Wire

Stay
Insulator
Ring
Insulator
7m 8m Reducer

Figure 5.2 : Overhead Service Line for Single Storey Building

5.5 Log-book Record

The trainer should ask the trainees to connect an Overhead service line
for a low rise building and tell them to prepare a report. The trainees
should record the actions taken and the equipment/parts used. The
record should be in the form of a work-log, or an action-taken report.
The length of the service line and the voltages at either end should also
be recorded.

35
Practical in
Power Distribution Answer the following questions :
Self Test

Q.1 Write the procedure to install overhead service line for single storey
building.

Q.2 Name the material which is used for stay wire and why stay wire is
needed?

Q.3 What are the main functions of rest insulator, aerial fuse, ring
insulator and stay insulator.

Q.4 Identify the various equipment used for protection of line personnel
performing a live line operation.

36
 Practical in
Activity No. 6 Power Distribution

PRACTICE OF IDENTIFICATION OF CABLE

JOINTING KITS AND TERMINATIONS

Structure
6.1 Objectives of Activity
6.2 Equipment/Materials/Facilities Required
6.3 Theory
6.4 Procedure
6.5 Safety Instructions
6.6 Self Test

6.1 Objectives of Activity

 After performing this activity, you should be able to

 make the technicians familiar with the different type

of cable jointing kits and terminations and make
them familiar with the jointing process.

 explain the safety measures to be taken.

6.2 Equipment/Materials/Facilities Required

 Cable

 Cable Jointing Kit

 Cable Lugs

 Jointing Sleeves

 Single Compression Brass Glands

 Impregnated Paper Tapes

 Tropoline Casting Resin System

 Tropoline Resin Based Sealing Putty

 Non-Magnetic Trefoil Clamps Type

 Composite Tool Box

 Compression Jointing Tools

 Scrapper Tool 37
Practical in
Power Distribution
6.3 Theory

A power cable is an assembly of two or more electrical conductors,

usually held together with an overall sheath. The assembly is used for
transmission of electrical power. Power cables may be installed as
permanent wiring within buildings, buried in the ground, run overhead, or
exposed. Flexible power cables are used for portable and mobile tools
and machinery.

Power cables of adequate current carrying capacity and voltage rating are
provided at the substation. Power cables are used for 33 kV, 11 kV or LT
system, to carry load current.

 Advantage of using Cables

As compared to overhead lines, cables have the following

advantages :

 The cable transmission is not subjected to supply

interruption caused by lighting or thunderstorms,
birds and severe weather conditions.

 It reduces accident caused by the breaking of the

conductors.

 Types of Cable :

 XLPE (Cross Linked Polyethylene Insulated Power Cable)

 PILC (Paper Insulated Lead Covered)

 PVC (Polyvinyl-chloride Cable)

 Oil-filled Cables

 XLPE (Cross Linked Polyethylene Insulated Power Cable)

Because of Excellent Thermal, Mechanical and Electrical

Properties XLPE Cables are being used extensively throughout
the world in all Power Stations, Industrial Plants, Chemical,
Fertilizer and Heavy duty Industries.

38 Figure 6.1 : XLPE Cable

 Practical in
Advantages of XLPE Insulation Power Distribution

 Higher current carrying capacity.

 Higher emergency and short circuit rating.

 XLPE is not prone to fatigue damage due to

vibration or heating cycles.

 XLPE are light in weight thus easy in handling during

manufacturing and Installation.

 Lower Dielectric losses.

 Better resistance to most chemicals, such as

ordinary acid, bases, oils.

 Jointing and termination are very easy.

 Better flexibility down up to – 40oC.

 PILC (Paper Insulated Lead Covered)

The paper insulation in power cable has been almost

superseded. It is quite cheap and has low capacitance and
high dielectric strength. It’s hygroscopic and its specific
resistance is of the order of 109 Ohm per cm. cube, but its use
depends upon its dryness; even a small amount of moisture
lowers its insulation resistance. So before use, the paper
insulation in it is impregnated in insulating oil. The maximum
o
safe temperature of paper insulated cable is 950 C approx.
The paper insulated cable should never be left unsealed. In
case of need, its end should temporarily be covered with wax
or tar.

Figure 6.2 : PILC (Paper Insulated Lead-Covered)

39
Practical in
 PVC (Polyvinyl-Chloride)
Power Distribution
It is a thermoplastic synthetic resin and is being widely used as
insulation. It has high electric resistivity, good dielectric strength
and mechanical toughness over a wide range of temperature.
Moisture, acids and alkalis do not affect PVC.

PVC insulated cables are usually employed for medium and

low voltage applications. A major use is for Domestic industrial
lights and power installations.

Figure 6.3 : PVC Insulated Cables

 Oil Filled Cables

In such cables the conductor are stranded around a hollow

cylindrical spiral of plain narrow metal strip.

The oil filled cables are of three types :

(i) Single core with an oil channel within conductor

(ii) Single core with sheath channel

(iii) Three core filler space channel.

Advantages of the Oil Filled Cables

 The requirement on thickness of the dielectric

decreases, which reduces the overall size and
weight of the cable.

 The thermal resistance of the cable decreases due

to decrease in dielectric thickness, which increases
the current rating of the cable.

 Perfect impregnation can be used.

 Cables can be impregnated after sheathing

40
 Practical in
 Jointing Kits Power Distribution

Types of Kits Cable Type

Heat Shrinkable XLPE and PILC

Push on Type XLPE

Resin Cast Type PILC

Tapex Type XLPE

 The Cable Constructional Details (as Per Lable)

 Conductor : Aluminum or Copper.

 Screen : Screened or Unscreened (for upto 3.3 KV).

 Inner sheath : Taped or Extruded, Normal or FR/FRLS

PVC.

 Armour : Armoured or Unarmoured. If armoured then flat

strips or round wires.

 Outer sheath : Normal ST-PVC or FR/FRLS FVC. Any

specific drum length with tolerance.

 Drum size : Any limitation on dimension/weight of drum.

 Any other special constructions.

 Joining Cables

In case of a cable breakage or in the event of a localized cable fault,

the two sections of the cable have to be joined, to restore continuity.

Type of Jointing Method

Type of Jointing Method Name of Power Cables

Heat Shrinkable Straight through Joint 11 KV, PILC

Heat Shrinkable Straight Through Joint 11 KV, XLPE Aluminum Cable

Heat Shrinkable Straight through XLPE/PVC Size of Cable

Heat Shrinkable Outdoor XLPE

Heat Shrinkable Transition Joint 11 KV Aluminum Cable

Heat Shrinkable Outdoors PILC Voltage 11 kV (Ue)

Heat Shrinkable Indoor XLPE

41
Practical in
Material Requirement
Power Distribution
 H.S Outer Jacketing Sleeve

 Main Sleeve

 Side Sleeve

 G.I. Wire Mesh

 H.S. Insulating Sleeve

 Earthing Material

 H.S. Adhesive Lined Breakout

 H.S. Oil Barrier Sleeve

 Glass Bedding Tape

 H.S. Stress Control Tubing

 H.S. Belting Oil barrier Sleeve

 Insulating Mastic

 Stress Control Mastic for Ferrule Region

 Crimping Type Inline Connector

 Mastic Sealing Tape

 Cable/Core Tie Wraps

 Mopping Cloth For Cleaning

 Core Cleaning Solvent

 Emery Sheet

 Types of Terminations
A joint is considered to be the weakest link in the system but the
overall reliability of a distribution system depends on it. Therefore,
jointing accessories and techniques have an important and critical
role; despite their comparative low value in the overall investment.

 Cast Iron Mould

 Epoxy Resin Type

 Heat Shrinkable

 Cold Shrinkable

 ‘Push On’ Type

42
 Practical in
6.4 Procedure Power Distribution

 Detection of Fault
Cable Faults

The fault that is most likely to occur is :

 A breakdown of the cable insulation, which allows

current to flow from the core to the earth, or to the
cable sheath, is called a ground fault.

 A cross or short circuit fault, in which case the

insulation between two cables or between two cores
of a multi core cable, is faulty.

 An open circuit fault where the conductor breaks or

a joint pulls out. The method for locating an open
circuit fault differs from those used in other two
cases.

In the case of multi-core cables, the insulation resistance of

each core to ground, and between cores should be measured.
If the fault is to ground, this will enable the faulty core to be
identified; and in case of a short circuit, the cores, which are
involved can be determined.

The fault may be of the type :

 Phase to ground fault

 Phase to phase fault.

 Cable Jointing
A joint is a connection between two lengths of cable, in which the
continuity of the conductor, the insulation and the protective covering
is maintained.

or

The making of a cable joint is to rebuilt the continuity of the

conductor and insulation system.

Assembly of the Joint

Degrease paper inner sheath next to the lead sheath and then
wrap glass bedding tape for a distance of 10 mm.

Put the Heat shrinkable belting oil barrier on the glass bedding
tape already applied and shrink with help of blow lamp/torch.
Avoid extra heating. 43
Practical in Put the Heat shrinkable stress control tube into position
Power Distribution
ensuring that 15 mm of the sleeve comes on the lead sheath
and balance on belting oil barrier sleeve. Shrink with the help of
blowlamp/torch.

Slide the heat shrinkable oil barrier sleeve from the end of the
cores and places them at position ensuring that they go down
into the crutch of the cable as much as possible. Carefully
shrink down barrier sleeve from bottom to top ensuring that
heat is uniformly applied around each tube. Allow to cool down.

Slide the breakout over the cores and pull well down into the
Crutch of the Cables. Hold down out with a plier to avoid
upward slippage. Commence shrinking the boot at the centre
working along them to the top and shrink completely.

Insert the heat shrinkable insulating tubing’s (say Q.1 and Q.2)
from the each end of the core and slides up to where the
jointing works will not be disturbed.

Connection Conductor

Insert the cable conductor into the ferrule after cleaning and
polishing the conductor.

After ensuring that two conductors meet end to end at the

centre of ferrule, compress the ferrule with compression die.

Compress in order from the centre of the ferrule to both ends of

the ferrule.

During the process of crimping, take care not to damage the

insulation.

Smoothen the surface of inline connector (ferrule) with the help

of smooth file or a sand paper.

Clean the surface of Insulation and ferrule with the help of

clean cloth soaked with cleaning fluid supplied with the kit.

Apply stress control tape on conductor sleeves and on bare

conductor on both sides of conductor sleeves.

Bring Insulation tube Q1 in position so that it equally covers the

core on both sides of the cable and shrink it with the help of
torch/blow lamp. Avoid extra heating.

Put the insulating tube Q 2 on the Insulating tube Q 1 and

shrink it with the help of blow lamp/torch.

Fix the main earthing connection with the help of copper

braided strip from lead to lead. Use plumbing metal for sealing
gap between the steel strip armour and lead sheath.
44
 Practical in
The continuity between armour and lead sheath shall also be
Power Distribution
achieved.
Relay the core as far as possible. Wrap two layers of G.I. mesh
around the cores with a 50% overlap. Cover the joint area upto
exposed armour. Bind the end of G.I. mesh with the help of
cotton tape and PVC tape provided in the kit. Fold back the
excess earth braid/s over the applied G.I. mesh and tighten it
with armour clamp on both sides. Cover armour clamps and all
sharp edges with the help of cotton tape or PVC tape.

Wrap mastic-sealing tape over the worm drive clamp. Slide the
heat shrinkable adhesive lined side sleeve on one side of the
G.I. wire mesh ensuring that about 200 mm of G.I. wire mesh is
covered under this and shrink completely. Slide the second
sleeve to the other side of the G.I. wire mesh and position it at
the prescribed position and shrunk completely.

 Cable Ends are Terminated by Providing

 Stress control screens

 Earthing clamp lead

 Insulation

 Lug rain sheds

Remember

While making joints and terminations, it is essential to know the

size and type of the cable in order to select appropriate kits for
joints and terminations. The kits contain the accessories
required along with instruction sheets for step-by-step
procedure for making joints and terminations. The cable and
end terminations should be prepared as per the dimensional
drawing and procedure given in the instruction sheet.

6.5 Safety Instructions

 To avoid accidents due to use, or fatal injuries-necessary
instruction given in the manual of the kit are to be followed.

 To avoid risk of accidental fire or explosion when using gas

torches, always check all connection for leaks before igniting
the torch, and follow manufacturer’s safety instructions.

 To minimize any effect of fumes produced during installations,

always provide for good ventilation of the confined workspace.
45
Practical in
Power Distribution Self Test Answer the following questions :

Q.1 In which conditions cables are used for transmission of electrical

power? Compare the advantages of using cables over overhead
lines.

Q.2 Write short note on various types of cable with their advantages.

Q.3 Describe construction details of a cable.

Q.4 During the crimping process, what care should be taken?

Q.5 Discuss various types of jointing kits and terminations. Write the
importance of cable ends terminations.

46
 Practical in
Activity No. 7 Power Distribution

PRACTICE OF MEASURING THE EARTH

RESISTANCE

Structure
7.1 Objectives of Activity
7.2 Equipment/Materials/Facilities Required
7.3 Theory
7.4 Procedure
7.5 Conclusion
7.6 Treatment for Minimizing the Earth Resistance Values
7.7 Self Test

7.1 Objectives of Activity

 After performing this activity, you should be able to

 explain the method of measuring earth resistance

of an earthing installation and its importance of
being low.

7.2 Equipment/Facilities/Materials Required

Earth tester – 1
Earthing installation under test – 1
Spike – 2

Connecting wires of negligible resistance.

7.3 Brief Theory

We already know that the value of short circuit current depends upon the
magnitude of earth fault loop resistance. In order that fuse should afford
sufficient protection, it is necessary that it should blow off quickly.

This is just possible only when the magnitude of fault current is sufficiently
high. In other words, for a given system voltage, it is important to keep the
magnitude of earth fault loop resistance of earth at consumer and earth
resistance at the substation or generating station as small as possible.

High earth resistance would also show up as higher voltage in the rest of
the circuit, posing danger to humans and equipment. Proper maintenance
47
Practical in
of electrical installation, therefore, requires periodic measurement of earth
Power Distribution
resistance.
 Methods of Earth Resistance Measurement
Three Terminal

In this method we use an Earth Tester (Figure 7.1), which has

four terminals, P1, P2, C1 and C2. The tester has a built-in
generator, operated by a rotating handle, and a meter to read
the resistance value.

To conduct this test, the earth tester terminals C1 and P1 are

shorted to each other and connected to the earth electrode
(pipe) under test. Terminals P2 and C2 are connected to the
two separate spikes driven in earth. These two spikes are kept
in same line at the distance of 25 meters and 50 meters due to
which there will not be mutual interference in the field of
individual spikes. If we rotate generator handle with specific
speed we get directly earth resistance on scale.

Note : Spike length in the earth should not be more than 1/20th
distance between two spikes.

RΩ
50

C1, C2

P1, p 2

Electrode
Under Test
G.L

25 M 25 M

Auxiliary spike
Figure 7.1 : Earth Tester for Measuring Earth Resistance

7.4 Procedure

Measurement of earth resistance is usually carried out by earth tester as

shown in Figure 7.1. Earth tester has D.C. generator and Ohm meter
current and voltage coils just similar to those in a Megger.

48
 Practical in
However, to avoid the effects of back e.m.f. due to polarization, as soil
Power Distribution
resistance is electrolytic in nature, A.C. is used in the test. For this
purpose current reverser is used which is mounted on the armature
extension of the D.C. generator. A.C. output taken from the reverser
brushes 3 and 4 is brought to current terminals C1 and C2 of the earth
tester – terminal C1 connected to earth electrode EE whose earth
resistance is to be found out. C2 is connected to an auxiliary earth
electrode AE2 spiked in earth at a distance of about 25 m. from EE.

When the Generator is driven, A.C. will flow from electrode EE to the
good earth, which has zero resistance and then will reach auxiliary
electrode.

Corresponding to A.C. flowing between brushes 3 and 4, D.C. will flow

through brushes 1 and 2 and current coil of the tester. As a result of
voltage drop taking place in the earth around the electrode, there are
formed equipotential shells around the main electrode EE and auxiliary
electrode AE2. The circular surface area on the ground bound by the last
equipotential shell which touches the good earth is called resistance area,
Figure 7.1.

DC
Current Generator
Reverser
1 4
1 2
53
8
Rectifier
7 6

dc dc

ac ac
ac ac

C1 P1 P2 C2

EE AE1 AE2

(a)

Good Earth
Equipotential Shell
(b)
Resistance Area
Resistance

(c)

Figure 7.2 49
Practical in
Outside the resistance area no voltage drop takes place. Electrodes EE
Power Distribution
and AE2 are taken so much apart that their resistance areas do not
overlap. If another auxiliary electrode AE1 is spiked in earth in between
the electrodes EE and AE2 then there should be no voltage drop between
AE1 and AE2. This A.C. voltage is picked up at terminals p1 and p2, which
is then rectified. D.C. output of rectifier at brushes 7 and 8 is applied to
voltage coil. If we move AE1 a few meters on a perpendicular line on
either side of the line joining EE and AE2, then the readings of resistances
so obtained should be same. This will be clear from Figure 7.2, which
shows how resistance varies between two electrode EE and AE2.

If the three readings taken after moving AE1 are not the same, it means
that the resistance areas of EE and AE2 overlap and we must take AE2
further away.

7.5 Conclusion

If the earth resistance is near about unity, it is normal. Too high value is
dangerous as it means low value of short circuit current, which may not
allow the fuse to operate.

Standard Earth Resistance Value

Major power station 0.5 Ω

Major sub-stations 0Ω

Minor sub-station 2.0 Ω

Neutral Bushing 2.0 Ω

Service connection 4.0 Ω

L.T. Lightning Arrestor 4.0 Ω

L.T. Pole 5.0 Ω

H.T. Pole 10.0 Ω

Tower 20-30 Ω

7.6 Treatment for Minimizing the Earth

Resistance Values

If earth resistance is more than the allowed values, following Treatment

can be used for minimizing resistance:

 Oxidation on joints should be removed and joints be tightened.

50
 Practical in
 Sufficient water should be poured in and around the earth Power Distribution
electrode.

 Earth Electrode of bigger size, as far as possible, should be

used.

 Electrodes should be connected in parallel.

 Deeper and wider Earth Pit can be made.

 Soil Treatment may be carried out around the Earth Electrode.

Self Test Answer the following questions :

Q.1 Why power station has very low value of earth resistance as
compared to the service connection of the house?

Q.2 Write the treatment for minimizing the earth resistance values.

Q.3 What is the importance of measurement of earth resistance?

Q.4 Describe the method of earth resistance measurement.

51
Practical in
Power Distribution

52
 Practical in
Activity No. 8 Power Distribution

PRACTICE OF INSPECTION AND ROUTINE

MAINTENANCE ACTIVITY OF A TRANSFORMER

Structure
8.1 Objectives of Activity
8.2 Equipment/Materials/Facilities Required
8.3 Brief Theory
8.4 Procedure
8.5 Self Test

8.1 Objectives of Activity

 After performing this activity, you should be able to

 make the technicians familiar with the method of

inspection and routine maintenance activity of a
transformer up to 1000 kVA.

8.2 Equipment /Materials/Facilities Required

 A Transformer (for inspection) up to or below 1000 kVA.

 Clamp/Clip-on meter.

 Transformer Oil Testing Set.

 Standard Tool Kit.

8.3 Brief Theory

With proper operation and maintenance, the expected life of a
transformer is 15 to 20 years, without need of any major repair work. As
compared to most other electrical equipment, transformer requires
relatively less maintenance. However in order to obtain a long and trouble
free service, it must be properly maintained.

The maintenance work can be divided into three categories :

 Routine Inspection or Routine Preventive Maintenance and

Minor Repairs.

 Medium Repairs.

 Major Repairs. 53
Practical in
The objective of maintenance of transformer is to obtain trouble free
Power Distribution
long life and ensure high reliability of supply.

 Routine Preventive Maintenance and Minor Repairs

This includes preventive maintenance work, which does not call for
opening the transformer cover.

 It includes visual inspection : Checking of filaments,

checking of the level of oil, cooling system fastening,
control circuit, oil level leakage, etc.

 The insulation resistance values are measured.

 The BDV (Break Down Voltage) of oil sample is

measured.

 The gas sample obtained from Buchholtz relay is

analysed.

 The nut bolts are tightened, the porcelain surfaces are

cleaned.

 Silica gel (de-humidifier) in the breather is replaced.

 The external fitments are repaired whenever necessary.

 The oil level is brought to desired value.

 The oil is filtered.

 Minor repair work is carried out by the operating

personnel in the substations.

 Medium Repair Work

This includes dismantling the transformer for inspection/repairs if the
core-coil assembly is to be accessible.

The sub-assemblies are inspected and repaired as necessary

(e.g. repair conservator tank, tap-changer, cooling system, sealing
gaskets, etc.).

The gaskets are replaced, if necessary.

The defects revealed in routine maintenance are removed during the

minor repair work.

The other minor repairs and maintenance mentioned earlier is also

carried out.

54
 Practical in
 Major Repair Work Power Distribution

Major repair work is carried out after a serious internal fault or after
prolonged service-life (8 to 10 years).

This involves opening-up of the transformer, replacement of

windings and insulation, tightening of the core laminations,
replacement of bushings, etc. Such repair work requires complete
dismantling of the transformer.
Major repair work is carried out by trained personnel, in a planned
manner preferably in a well-equipped repair-workshop, perhaps the
vendor’s factory.

Procedure

Typically, the supplier specifies the transformer maintenance schedule

and the procedure. The following is a general guideline.

 Typical Maintenance Schedule for Transformers up to

1000 kVA
Frequency Inspection Inspection Action Required if
of Details Conditions are
Inspection Unsatisfactory
1. Hourly* Load (amperes) Check against Start fans if
Temperatures, rated figures necessary
Voltage
Check that air If silica gel is pink,
2. Daily Dehydrating
passages are change; may be
breather
clear. Check the reactivated for use
colour of the again
active agent

3. Monthly Check If low, top up with dry

Oil level in
transformer oil oil. Examine
transformer
level transformer for leaks.

4. Quarterly Bushings Examine for Clean or replace

cracks and dirt
deposits

5. Half- No conservator Check for Improve ventilation,

yearly moisture cover check oil

6. Yearly Oil in transformer Check for Take suitable action

dielectric to restore quality of
strength and oil
water content.

55
Practical in ” Earth resistance Check for acidity Take suitable action
Power Distribution and sludge. if earth resistance is
high

Relays, alarms, Examine relay Clean the

“ and alarm components and
their circuits etc.
contacts, their replace contacts and
operation, fuses fuses if necessary.
etc. check relay Change the setting if
accuracy etc. necessary.

7. Two Non-conservator Internal Filter oil regardless

Yearly transformer inspection of condition
above core.

8. Five Overall Wash by hosing

Yearly  inspection, lifting down with clean dry
or after of core and oil.
internal coils.
fault

It may be considered :

From 1 to 6 as minor repairs

7 as medium repair

8 as major repairs

A rigid system of preventive maintenance will ensure long life.

Log books and history – records should be maintained for each transformer.

No work should be done on the transformer unless it is disconnected from

supply, and the terminals, tank and the cover are solidity earthed.

 Typical Maintenance Schedule for Transformers above

1000 kVA (For Information)
Sl. Frequency Inspection Inspection Details Action
No. of Required if
Inspection Conditions are
Unsatisfactory
1. Hourly Ambient Check that If abnormal
temperature temperature is heating, shut
reasonable down the
Winding
“ transformer and
temperature
investigate if
heating is
persistently
higher than
normal
Oil Temperature Check against rated
“
Load (amperes) figures
Voltage
56
2. Daily Oil level in Check against If low, top up Practical in
transformer with dry oil, Power Distribution
transformer oil level
examine
transformer for
leaks
“ Oil level in bushing
“ Leakage of water Replace if
into cooler cracked or
broken
“ Relief diaphragm
“ Silica-gel breather Check that air If silica-gel is
passages are free. pink change by
Check colour of spare charge.
active agent The old charge
may be
reactivated for
use again

Quarterly Bushing Clean or replace

Examine for cracks

“ Oil in transformer and direct deposits
3. Take suitable
action to restore
Check for dielectric quality of oil
strength and water
Cooler fan content
“ bearings, motors Replace burnt or
and operating worn contacts or
Lubricate bearings. other parts
mechanisms Check gearbox.
Examine contacts
check manual
control and
interlocks

4. Half yearly Oil cooler Test for pressure

5. Yearly or Oil transformer Check for acidity

and sludge. Filter or replace
earlier if the
transformer
can
conveniently
be taken out
for checking
“ Oil filled bushings Test oil Filter or replace

“ Gasket joints Examine Replace

compounds for gaskets, if
leaks leaking

“ Cable boxes Check for sealing Tighten the

arrangements for bolts evenly to
filling holes avoid uneven
pressure

“ Surge diverter and Examine for crack Clean or replace

gaps and dirt deposits 57
Practical in “ Relays, alarms, Examine relay and Clean the
Power Distribution their circuits, etc. alarm contacts, components and
their operation, replace contacts
fuses, etc. Check and fuses, if
relay accuracy, etc. necessary.
Change the
setting if
necessary

6. 5 yearly Take suitable

Earth Resistance
action; if earth
resistance is
high.
Overall inspection Wash by
1000 to 3000 kVA
including lifting of housing down
core and coils. with clean dry
coil.

58
 Practical in
Power Distribution
Self Test Answer the following questions :

Q.1 Write the importance of maintenance of transformer.

Q.2 Give short notes on minor, medium and major repairs for a
transformer.

Q.3 Give various inspection details and the action required if conditions
are not satisfactory during routine maintenance for transformers upto
1000 kVA? Consider frequency of inspection : daily, quarterly and
yearly.

59
Practical in
Power Distribution

60
 Practical in
Activity No. 9 Power Distribution

PRACTICE OF TROUBLE SHOOTING AND

MAINTENANCE ACTIVITY OF SWITCH GEARS

Structure
9.1 Objectives of Activity
9.2 Equipment/Materials/Facilities Required
9.3 Theory
9.4 Procedure
9.5 Log Book Record
9.6 Self Test

9.1 Objectives of Activity

 After performing this activity, you should be able to

 make the technicians familiar with the method of

inspection and routine maintenance activity of switch
gears.

9.2 Equipment/Materials/Facilities Required

 LT/HT Switchgear

 Clamp-on Meter

 Multi Meter

 Standard Tool Kit

 HT Neon Testor (For HT)

 Discharge Rod

 Earthing Rod.

9.3 Theory
Switchgears are mechanical devices designed to close or open the
contact members in an electrical circuit under normal or abnormal
conditions.

The selection of switchgears depends upon the following points :

 Working voltage.

 Loading current. 61
Practical in
 Fault current level.
Power Distribution

 Atmospheric conditions.

 Types of operation, i.e. manually operated, remote controlled,

pneumatically controlled, etc.

Types of Switchgears
Two main types of switchgears are :

 L. T. switchgears, which can further be divided into

two types.

 Air circuit breaker and

 Oil circuit breaker

 H. T. switchgears.

 L. T. Switchgears
These consist of earth fault protection and over load protection and
no relay is connected in the circuit.

The maximum capacity of L. T. switchgears is 1600 amps. Capacity

of these switchgears is selected according to the load requirements.
The capacity of incoming and outgoing cable in the panel board is
also selected according to the capacity of switchgears installed on
the panel board.

Sometimes couplers are also used in the panel boards with bus-bars
to connect the supply alternatively according to the load demand and
to increase the life of the switchgear.

If the contacts are placed in oil, the switchgear is known as oil

circuit breaker, otherwise it is known as air circuit breaker.

Air Circuit Breakers

Such circuit breaker consists of two fixed contacts mounted

one above the other in a vertical plane. When the breaker is
closed, these contacts are stuck together under heavy
pressure by a sticking member operated by a system of
linkages.

Parallel arcing contacts are made of carbon alloy or copper-

tungsten alloy to save the contact points from getting damaged
due to repeated arcing. The arcing and auxiliary contacts close
before and open after the main contacts come in operation.
62
 Practical in
A latch is used to hold in position the breaker, which may be
Power Distribution
operated electrically or mechanically. Such type of breaker is
mostly used on d.c. circuits and low voltage a.c. circuits, upto
600 V, for the protection of the general lighting, power and
motor circuits.

Oil Circuit Breaker

In such circuit breakers, the current carrying contacts are

immersed in transformer oil. The oil help in quenching the arc
faster and also works as a cooling medium.

When the current is passed through the contact of the circuit

breaker is interrupted by opening the contacts, the current
continues as an arc, which is maintained due to the ionization
of the molecules between the contacts.

The energy produced by the arc between the contact points is

absorbed by the oil and the arc space is kept cool. When the
current is zero, the pressure of hot oil above the contacts
forces the cool oil into the contacts space which works as an
insulating agent between the contact space and avoids the
re-striking of the arc.

 H. T. Switch Gears
These switchgears consist of :

 Protection Devices – Relays (one numbers earth fault

relay and two numbers over current relays fed by a
battery circuit of 24 V, or a rectifier)

 Operating mechanism

 Circuit breakers

 Instrument – Current Transformer (CT) and Potential

Transformer (PT).

Protection Devices

Earth Fault Protection : When any one of the phases is

earthed, the current in the different phases is unbalanced. In a
normal system in which the neutral is earthed, the current
equal to vector sum of currents in the three different phases will
flow through the neutral conductor. In a balanced circuit, this
current is zero. In the case of earth fault, the relay connected to
the neutral will be energized due to the net current and will
close the trip circuit.
63
Practical in
The earth protection can also be obtained by inserting three
Power Distribution
current transformers in the three different phases by
connecting their secondary’s across the relay operating coil to
energise it. When the earth fault occurs, unbalancing of
currents is produced in the phases, which energise the relay
operating coil due to their vector sum thereby closing the trip
circuit.

Over Current Protection : In this system, three star connected

current transformers are installed in the three phases (one in
each phase) and three star connected relays are connected in
series with secondary’s of these. When excess current flows
through any of the phases or through all phases, the relay is
operated, closing the tripping coil circuit. The tripping coil after
getting energized trip the circuit breaker.

Operating Mechanism

The H. T. switchgears consist of closing, tripping and

interlocking mechanism of circuit breakers, usually connected
to a common bus bar. The isolators are provided on both sides
of the circuit breakers to disconnect them or to make them
dead from live parts to keep them ready for repairs and
maintenance without any danger. The electrical or mechanical
interlocking helps the circuit breaker to open before opening
the isolators and isolators are opened before opening or
removal of any cover or barrier.

9.4 Procedure
Maintenance of Air Circuit Breakers

Sl. Parts to Maintenance Action Time

No be Period
Inspected
1. Main Using a fine file, file the pitted contacts, Half yearly
Contacts clean the surface with petrol or
and moving recommended chemical and lubricate
contacts with suitable lubricant like Vaseline, if
necessary
2. Arcing Clean the contact surface with fine cloth Quarterly
contacts and petrol, but do not lubricate them
3. Bus bars Tighten the joints, if there is any loose Half yearly
joint.
64
 Practical in
4. Earthing Check the earth connections, its Yearly Power Distribution
continuity and tighten the connections,
if found loose.
5. Bearings Clean the rusted bearings and joints Yearly
and joints with petrol and re-grease the bearings
with proper grade grease.
6. Visible Clean with petrol and lubricate with Half yearly
break Vaseline.
blades
7. Insulated Cleaning of dust and dirt Half yearly
parts

Maintenance of Oil Circuit Breakers

Sl. Parts to Maintenance Programme Time Period

No. be
Inspected
1. Main File the contacts with smooth file if (a) Quarterly in
contacts badly pitted and clean them with case of heavy
and moving emery cloth and then with fine duty
contacts cloth. If the contacts are burnt,
(b) Yearly in case
replace them.
of normal duty

2. Arc control Check the control device for (a) Quarterly in

device carbon deposits. Remove it with case of heavy
blunt edged tool and wash the duty
surface with Kerosene oil.
(b) Yearly in case
Replace the burnt plates or
of normal duty
replace the whole assembly for
better performance. (c) Quarterly in
heavy duty
(d) Yearly in normal
duty

3. Connecting Inspect all the pins, screws and Half yearly

rods and nuts and tighten them properly, if
levers found loose. Lubricate them with
proper grade heavy machine oil.

4. Closing and Operate the circuit breaker by Yearly

tripping hand to see its proper and correct
mechanism mechanism operations. Lubricate
the closing mechanism with
recommended grade machine oil.
Use firm and smooth fabric for
cleaning purpose replace worn out
parts. 65
Practical in
Power Distribution 5. Oil level Inspect the level of the oil in the Quarterly
guage gauges. Top it with dehydrated oil,
if level is found low.

6. Insulating Check the condition of the oil and (a) Quarterly in

oil take the sample oil to test it for its case of heavy
correct dielectric strength in the oil duty
testing set. Drain out the dirty oil
(b) Yearly in case
and refill it with fresh, having
of normal duty
proper dielectric strength oil. The
dielectric strength should be
checked after each 12 medium
fault interruptions.

7. Contact Check the contact resistance and Yearly

resistance record them

8. Insulators Inspect the porcelain and Half yearly

bushings for cracks and breakage
and replace the broken units. The
cracked porcelain causes leakage
and cracked bushings allow the
leaking oil. Clean also the dust
and carbon, because it lowers the
insulation resistance causing
flash-overs.

9. Relay Check all relay for correct Half yearly

setting operation with a relay testing set.

10. Indicating Check the indicating devices and Yearly

Devices lamps. If found defective, correct
them or replace them.

Troubleshooting of Circuit Breakers

Sl. Main Faults Causes Remedies

No.

1. Overheating This is due to (1) Replace the burnt

contacts or clean
(1) Burnt contact or when
the carbon deposits
carbon is collected on
with fine cloth
the contact surface
(2) Check and reduce
(2) Over loading
the load to within
(3) Misalignment of
limits
contacts
66
 Practical in
(4) Improper surface of (3) Set the contacts in Power Distribution
contacts the proper order

(5) Improper ventilation of (4) Smooth them with

substation emery paper or
smooth file and
(6) Improper condition of
clean them
oil
(5) Maintain the proper
ventilation

(6) Replace the old oil

with fresh oil

2. No tripping This is due to (1) Replace the trip coil

(1) Shorted trip coil (2) Replace the relay

(2) Shorted operating coil (3) Replace the latches

(3) Slipping of plunger from (4) Tighten the

the latches connections

(4) Loose connections of (5) Get the bettery

battery charged

(5) Discharged battery (6) Replace the spring

(6) Low tension of spring (7) Set the contacts

correctly
(7) Relay contacts do not
make contact

3. Magnetic (1) Switch may be (1) Replace the switch

switch defective
(2) File the surface of
(2) Relay contact may be the contacts and
welded together clean them

(3) Plunger may remain (3) Correct the lever or

stuck onto the lever or replace it
latches

 Maintenance of Metal Clad Switches

For the maintenance of metal clad switches inspect the different parts of
the switches from time to time for its easy and efficient operation and to
increase its life to operate smoothly.

67
Practical in
Power Distribution
Maintenance of Metal Clad Switches

 Check the handle for its easy operation, if lever is not working
properly, set it or oil it.

 Check the tension of the spring, if it has low tension replace it.

 Check the pins of the cover and handle, if loose, tighten them
and if broken, replace them.

 Check the contact strips, if not making contacts with the

terminals strips, bend them little to make the contacts properly.

 Check the insulating fibre rod, if found cracked, replace it.

 Check the terminals screws if missing or loose, replace it.

 Check the fuse grips and base, if found cracked or broken

replace them.

 Check the connections, if found loose, tighten them.

9.5 Log-book Record

Open a switchgear, preferably one not in use, else totally isolated from
the live circuit, and identify all the parts. Disassemble and then
re-assemble the switchgear fully. Maintain a log of every action taken
and the condition of each part. This exercise must be undertaken under
proper supervision?

68
 Practical in
Power Distribution
Self Test Answer the following questions :

Q.1 List the troubleshooting of circuit breakers in terms of main faults,

causes of faults and their remedies.

Q.2 Fill the blanks given below :

Maintenance of Air Circuit Breakers

o be Maintenance Action Time

cted Period
--------------------------------------------------------------------------------------------------------------------------- Half
cts -- yearly

g
ts
g --------------------------------------------------------------------------------------------------------------------------- Quarterly
cts --

Maintenance of Oil Circuit Breakers

o be Maintenance Action Time

cted Period

g --------------------------------------------------------------------------------------------------------------------------- Yearly
-
ng
nis

vel --------------------------------------------------------------------------------------------------------------------------- Quarterl

- y

69
Practical in
Power Distribution

Activity No. 10
70
 Practical in
PRACTICE OF INSTALLATION AND SEALING OF Power Distribution

ENERGY METERS

Structure
10.1 Objectives of Activity

10.2 Equipment/Materials/Facilities Required

10.3 Brief Theory

10.4 Procedure

10.5 Precautions

10.6 The Points to be Remembered

10.7 Self Test

10.1 Objectives of Activity

 After performing this activity, you should be able to

 make the technicians familiar with the techniques and

methods of installation and sealing of energy meters.

10.2 Equipment/Materials/Facilities Required

 Different types of Energy Meter

 Service Cables of different size

 Meter Boxes

 Meter Seals

 Clamp/Clip-on meter.

 Electric/Hand Drill

 Drill bits

 Ball peen hammer

 Standard Tool Kit.

71
Practical in
Power Distribution
10.3 Brief Theory

The distribution company charge a customer for the power consumed. As

this is the basic source of revenue for the company, and also as per the
law, it has to install an accurate electric/energy meter at the customer’s
premises.

An electric meter or energy meter is a device that measures the amount

of electrical energy supplied to customer. Utilities record the values
measured by these meters to generate an invoice for the electricity.

At present, energy meters based on electromagnetic technology and

static meters are being used in the Indian Distribution Network.
Single-phase meters are being used for most of the domestic and
some commercial consumers, whereas 3-phase meters are being
used for industrial, agricultural and large commercial consumers.

Energy meters typically consist of :

An energy measurement apparatus for measuring the energy

consumption and a gauge that is visible outside the meter, showing the
amount of electrical quantities including the energy consumed. Electricity
meters track among other things, the amount of energy consumed,
typically measured in kilowatt-hours (kWh), at each customer's facility.

The available technology options for metering are given as follows :

Available Technology Options for Metering

(i) Electromechanical meters;

(ii) Hybrid meters;

(iii) Static (electronic) meters;

(iv) Demand meters;

(v) Multiple tariff (variable rate) meters/Time of Usage (TOU) meters;

(vi) Prepaid meters;

(vii) Automatic Meter Reading (AMR) and Remote Meter Reading (RMR).

LOGIES
72
 Practical in
Power Distribution

(a) (b)

Figure 10.1: (a) Electromechanical Energy Meter, and (b) Electronic Meter

 Electromechanical Meters
Electromechanical energy meters (Figure 10.1(a)) are based on the
rotating disc Principle. The working of these meters is explained in
the Box below.

Working of Electromechanical Meters

The meters have a revolving metallic disc mounted on jewel
bearings/magnetic suspension bearings. The display is cyclometer or
mechanical counters and accuracy is typically 1% or 2%
(class 1.0 or 2.0).

They cater to limited tariffs applicable mainly to 1-phase 3-phase

direct connected segment (whole current meters). The
electromechanical induction meter operates by counting the
revolutions of the disc, which rotates at a speed proportional to the
power consumed. The number of revolutions is, thus, proportional to
the energy usage. The metallic disc is acted upon by three magnetic
fields, one proportional to the voltage, another to the current and a
third constant field supplied by a permanent magnet. One of the
varying fields induces currents in the metallic disc, which are then
acted upon by the other varying field to produce a torque. This results
in the torque being proportional to the product of the current and
voltage, i.e. power.

As the metallic disc rotates through the permanent magnetic field,

eddy currents are again produced which dissipate energy (since the
disc has some resistance) and act to slow the rotation. This drag is
proportional to the rotation speed. The equilibrium between the applied
torque and the drag results in a speed proportional to the power. The
rotating disc in this type of meter is, in fact, an electric motor of a type
called a reluctance motor or eddy current motor. It consumes a small
amount of power, typically around 2 W.
73
Practical in  Static (Electronic) Energy Meters
Power Distribution
Electronic energy meters (Figure 10.1(b)) are replacing traditional
electromechanical meters in many residential, commercial and
industrial applications because of the versatility and low-cost
afforded by electronic meter designs.

The measurement circuits are electronic with LED (Light Emitting

Diode)/LCD (Liquid Crystal Display) display and their accuracy is
typically class 0.2, 0.5, 1.0.

They cater to multiple tariffs for all segments CT-VT (Current

Transformer-Voltage Transformer) operated, CT operated,
1-phase or 3-phase Direct connected segment.

These meters measure and record active, reactive and apparent

demand/energy. The static energy meters are microprocessor
based and have non-volatile memory to record and store data.

The electronic meter, in its basic form has : A power supply, a

metering engine, a processing and communication engine, i.e. a
microcontroller, other add-on modules such as Real Time Clock
(RTC), LCD display, communication ports/modules, etc.

These meters are extremely difficult to tamper with, and if

somebody does attempt to tamper with it, it will send alarm signals
and record the information. The programmability of microprocessor
has become a useful tool for incorporating different features like
tamper data, import-export, time-of day metering, load pattern
analysis, etc.

They can be made SCADA (Supervisory Control and Data

Acquisition) systems compatible. They can have communication
ports to support AMR/RMR on various communication platforms, as
well as, for downloading of data on external storage devices.

 Prepaid Meters
Prepaid metering is a system whereby consumers purchase
electricity through a smart card. The amount paid, together with
other information, is encoded on a smart card (fitted with a
microprocessor).

In order to transfer the credit, the consumer inserts the card in a

compatible meter. The meter reads the data and when the pre-paid
amount of energy has been used up, power to the consumer is
disconnected.

74
 Practical in
The consumer gets the card reloaded/reprogrammed. The system Power Distribution
has the capability of programming with multiple rates, time of use
tariffs, etc. The consumer can read, among other data, the
remaining money, on the display of the meter.

The use of prepaid meters results in almost total elimination of

non-payment and delayed payment and enables transfer of reliable,
accurate and up to date consumption and billing data according to
tariff policy in use. This information can be utilized by the utility for
demand forecasting and for controlling peak demands. It also means
substantial reduction in staff for meter reading, bill serving, bill
complaints and bad debts, etc.

Figure 10.2 : Prepaid Meter

Full meter programmability allows maximum flexibility in changing

tariffs. Consumer can also decide in advance the affordable level of
expenditure, which may helps him and the utility in elimination of
disputes regarding inaccurate bills.

Automatic Meter Reading (AMR) and Remote Meter Reading

(RMR) describe various systems that allow meters to be checked
without the need to send a meter reader out. This can be effectively
achieved using off-site metering, that is an electronic meter is placed
at the junction point where all the connections originate, inaccessible
to the end-user and it relays the readings via the AMR technology to
the utility.

Remote metering enables online metering of energy consumption. It

is particularly useful for high value consumers where accuracy of
billing and delays in time taken for meter reading are important.
Monitoring of consumption patterns to detect theft/tampering of
meters is possible with these types of meters. 75
Practical in
The remote metering unit may be the RTU (Remote Terminal Unit),
Power Distribution
which receives the pulses generated by the electronic meters and is
connected to the Central PC (Personal Computer) Station through a
communication system, which could be PLCC (Power Line Carrier
Communication), public switched telephone network, radio, etc.

 Single-phase Meters
Single-phase meters are generally rated for 240 V AC supply; the
current ratings are 5/10, 10/20, 2.5/10 or 5/20 A and are for direct
connection to the mains. They start registration with small load of
about 6 W and record up to 4800 W.

The main feature of a single-phase meter (electromechanical

induction type) is its simplicity, compactness and robust design. It
comprises a potential coil and a current coil. The potential coil is
fitted on the middle limb of an E-shaped electro-magnet and
connected across the supply mains.

Similarly, the current coil consisting of a few turns of heavy gauge

copper wire is wound on two limbs of a U-shaped electro-magnet.
The two fluxes, produced by the voltage (pressure or potential) coil
and current coil, create a mechanical torque on the non-magnetic
aluminum disc (which is located between the 2 coils) causing it to
rotate.

A brake magnet of C-shaped alloy steel is provided to control the

movement or rotation of the disc set up by two fluxes. The disc
rotates through the narrow air gap of the C-shaped magnet and eddy
currents are set up, which interact with the field and exert braking
effect.

10.4 Procedure

 Energy Meters – Installation and Commissioning

The meters are connected before the consumer’s isolating device
(Main Switch), which may be a molded case circuit breaker,
miniature circuit breaker or an ironclad switch fuse unit. At the time
of commissioning, each meter is tested at site by the owner. A
reference standard meter of 0.2 class or better is used for testing.

 Supply Side Wiring

The supply side wiring is the responsibility of the utility and the
following must be ensured while carrying it out.
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 The supply wires provided are of suitable rating. Power Distribution

 In case of more than one meter on one service line, it is

preferable to use bus-bars. When a number of meters are
connected to a single distribution mains, for registering
electricity supplied to different consumer loads, separate
service lines – phase(s) and neutral, are used for each
meter. Each independently metered consumer load is
directly connected to the distribution mains through its
meter connected in specified phase sequence so as to
meet accuracy requirements of relevant standard.

 The supply wire is properly terminated.

 The connection is as per connection diagram mentioned

on meter.

 Utility should use its own earthing for its devices. Utility
provides phase and neutral (Single Phase) supply to
the consumers. The neutral is used for carrying return
current only. The neutral of one consumer should not be
connected to other consumers who have independent
and separate supply connection.

Utility provides separate neutral to each consumer up the

metering point and same is used by the consumer. The
consumer ensures that all the correct wiring practices are
followed and neutral is not looped with other consumers
or meters in the same premises. Consumer should not
earth the neutral after the metering point. Wherever there
is multiple meter installations, bus bar arrangement is
used for neutral, so that looping is avoided.

 Installation of Meters and Verification of Connections

Apart from testing and calibrating the meters they must be properly
installed as per the connection diagram.

The points that must be kept in view while meters are installed are
given in the Box below.

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Practical in
Power Distribution Installation of Meters

(a) Position of meter should be such that reading is easily

visible.

(b) Mounting of meter should be on solid wall or DP structure or

on panel board.

(c) Vertical mounting of meters should be ensured. The utility

engineer should use a plumb bob and mark a vertical line
prior to installation. He could also use a spirit level and put
on the top of the meter after hanging on the screw hole.
Alternatively, he should put spirit level on the edge of the
terminal block to ensure vertical mounting.

(d) For HT metering equipment, CTs should be right on the

incoming side before the point of isolation.

(e) The meter box should be sealed.

(f) The meter recording should be checked at site.

10.5 Precautions

The following should also be ensured :

 Appropriate crimping device should be used for crimping the

lugs. Thimbles should be of appropriate configuration (pin type,
fork type, etc.) to match with the terminal block, for low current
connection. For high current terminations, crimping should be
used with cable crimping tools and multiple point crimping
should be done for the lugs used for higher current ratings.

 If the terminal block is of MS cage clamp type, there is no need

to use any lugs and the copper cables can be directly
terminated at the clamp.

 The recommended tightening torque must be exerted on the

screw to ensure proper tightening of the terminations. It is
recommended to use proper tools, equipments for this
purpose.

 Usage of lugs as per the recommendation of manufacturer and

ensuring proper crimping will protect the joints from failures.

 For high current terminations, tensile test and shock test should
be performed after crimping the lugs.
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 Where aluminum cable termination is to be done on copper Power Distribution
bus bars or brass studs, bimetallic type of lugs should be used.

 Some meters have lower terminal pitch. Because of this,

cables foul with each other while installation. Proper cable size
according to the meter rating should be defined.

 Aluminum conductor cables should be replaced by copper

cables for the whole current meters.

For indoor meters, the wiring should be done such that the cables enter
the meter box from the bottom or rear side. This is not only aesthetic, but
also prevents the service cable from tampering, etc.

10.6 The Points to be Remembered

The points that should be verified after installation of the metering system
are given in Box.

Points of Verification

(i) Phase association

(ii) CT polarity

(iii) VT polarity

(iv) Phase angles

(v) Phase sequence

(vi) System conditions – unbalanced capacitors

(vii) Actual CT/VT ratio

 Sealing Points

The meter seal should be tamper proof. The consumer should be

briefed about seals. The sealing of all metering systems should be
done at various points (as applicable) to avoid tampering. There
should be at least one seal at all points mentioned below
(wherever applicable) :

 CT Secondary Boxes (in addition to locking arrangement).

 PT Secondary Box (in addition to the locking

arrangement).

 Meter Cabinet.
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Power Distribution  Meter Test Block.

 Meter Terminal Cover.

 Meter Cover.

 Panel doors where CT and PT secondary circuits are

terminated or where possibility for shorting or breaking
exists and fuses/links are provided.

 PT selector relay box where automatic change-over of

potential supply to meter from one PT to another is
provided.

 CT Primary Links and Top Covers.

 MD Reset Push Button.

 Boxes/Cabinets containing terminals for remote

transmission of metered data via communication
channels, junction boxes in the system and boxes
wherein interface devices are mounted.

 Meter reading port.

Seals are necessary to guard against tampering with the

connections and internal parts of a meter. Tampering of seals will
give consumers access to the relevant part of a meter installation
where s/he can manipulate the unit to record less energy leading to
commercial loss. A seal is placed to detect unauthorized entry to the
meter internals.

The effectiveness of the seal depends on the type of seal (whether it

is tamper proof or not, whether a duplicate can be obtained or not,
etc.), and the procedures used in tracking the seals.

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Power Distribution
Self Test Answer the following questions :

Q.1 List the different types of energy meters.

Q.2 What are the advantages of electronic meter over electromagnetic

meter?

Q.3 Highlight the salient features of electronic meter.

Q.4 Discuss the various available technology options for metering.

Q.5 Describe the important points that must be kept in view while meters
are installed.

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Power Distribution

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Activity No. 11 Power Distribution

PRACTICE OF TESTING OF DOMESTIC WIRING

INSTALLATIONS

Structure
11.1 Objectives of Activity
11.2 Equipment/Materials/Facilities Required
11.3 Brief Theory
11.4 Circuit Diagram
11.5 Procedure
11.6 Observations
11.7 Precautions
11.8 Self Test

11.1 Objectives of Activity

 After performing this activity, you should be able to

 ensure safe and satisfactory, trouble free long working

life, the testing of domestic installation is considered
essential on the following occasions :

 Before putting a new installation in service and

connection and re-connection of supply mains.

 Whenever a change, addition or modification in

the existing wiring is done.

11.2 Equipment/Facilities/Materials Required

 A continuity tester or a low voltage source with suitable
indicating system.

 Ohm-meter.

 Megger/insulation resistance tester.

 Pliers combination

 Screw drivers

 Standard Tool Kit. 83

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Power Distribution
11.3 Brief Theory
The following tests are carried out on the installations initially and at
regular intervals, and a record is maintained or a certificate is given.

 Continuity test of the electrical circuits.

 Polarity checking of all single pole switches and 3-pin sockets.

 Insulation test.

 Earth continuity test.

11.4 Circuit Diagram

P Fuse Switch Close
Load Side
Terminals
N Shorted
P

Continuity
Tester

Figure 11.1 Continuity Test

Fuse Switch
P

Metal Conduit

L E
N L
P N
P

Megger

Figure 11.2 : Insulation Test on Circuit to Earth (Conduit)

Out Going Circuits

E
N

N P
P
N
N
N 3 Pin Socket

84 Figure 11.3 : Testing of Polarity of Switches and Three Pin Socket

 Practical in
11.5 Procedure Power Distribution

(i) Disconnection the supply from the existing installation and

remove the main switch fuses.

(ii) Disconnect all loads like fans, lamps, tube lights, stabilizers,
electric bell, buzzer, heaters, ovens, geyser etc. if already
connected.

Let us discuss some important tests which are carried out on the
installations :

 Continuity Test

Check one circuit at a time from the output of the respective fuse to
the neutral strip with a continuity tester; after removing the fuse, note
the indication. A lighted lamp or deflection on the instrument shows
“continuity’, and no indication shows, open circuit or high resistance
joint. Record the result of each circuit. Replace each fuse after the
test.

 Testing for Polarity of Single Pole Switches and

Sockets

(i) Open all the switchboards and check that all switches control
the phase line.

(ii) Check that all 3 – pin sockets have the phase on the right hand
side pin at the base facing the socket and is controlled by a
switch. Close all the switchboards.

 Insulation Resistance Test

Insulation resistance is carried out by using a 500 V megger or

insulation resistance tester.

Before checking, test the instrument for correct indication :

(i) Short the output leads and rotate the handle. The pointer
should deflect to zero on the scale.

(ii) Keep the leads open, and rotate the handle. The pointer
must stay at infinity point on the scale.

(iii) Connect the tester’s ‘line’ terminal to the output of the

main switch and the earth terminal to the earth of the
switch casing. Rotate handle and note the reading.
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(iv) Pointer showing infinity or close to this point on the scale
Power Distribution
shows good insulation.

(v) Pointer showing away from infinity but not close to zero
shows bad or poor insulation.

(vi) Pointer showing zero or close to it indicates a short circuit

to earth.

(vii) Record each reading.

(viii) Check phase line to earth and record the reading.

 Earthing
To ensure continuity in earthing, all the metallic conduits, iron boxes,
iron clad switchboards, earthing points on various light and power
sockets must be connected electrically to the main earth and must
not have a resistance value of more than 1 Ohm (to earth) when
checked with an ohmmeter.

11.6 Observations

The result of all the tests must be recorded in the following format :

Sl. No. Test Reading Observation Result

1 2 3 4 5

1 Continuity Test

2. Insulation Test

(i) Conductors to earth

with load terminals
shorted

(ii) Phase to neutral –

Lead

(iii) Phase to earth –

Terminals

(iv) Neutral to earth –

Open

3. Polarity Test

4. Earth Continuity Test

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11.7 Precautions Power Distribution

 Always disconnect the supply before attempting any test.

 Always check the megger, the ohm-meter and the continuity

tester before use.

 Bring the circuit to normal working conditions after testing and

reconnect the supply.

 Always record the results.

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Practical in
Power Distribution Answer the following questions :
Self Test

Q.1 What is megger? What do you understand if pointer of megger

shows infinity or zero?

Q.2 Discuss various necessary tests which are carried out on the
domestic wiring installations?

Q.3 What do you mean by Ohm-meter?

Q.4 Draw the circuit diagram for continuity test.

Q.5 What precautions should be taken while testing of domestic wiring

installations?

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 Practical in
Activity No. 12 Power Distribution

PRACTICE OF IDENTIFICATION AND LOCAITON

OF VARIOUS FAULTS IN HOUSE WIRING AND
THEIR RECTIFICATION

Structure
12.1 Objectives of Activity
12.2 Equipment/Materials/Facilities Required
12.3 Brief Theory
12.4 Procedure
12.5 Some Common Wiring Faults in Tabular Form
12.6 Observation Table
12.7 Precautions
12.8 Self Test

12.1 Objectives of Activity

 After performing this activity, you should be able to

 understand the functioning of an electric circuit.

 establish a clear concept of three essentials of the
circuit, i.e. source, circuit elements, and the connected
load.
 analyze the faults with reasoning, locate them and to
carry out rectification.

12.2 Equipment/Facilities/Materials Required

 Insulated combination pliers
 Set of common screwdrivers
 test lamp
 neon tester
 fuse wires 5 amp and 10 amp
 insulation tape – PVC self adhesive, or black cotton self
adhesive
 knife
 multimeter
 megger

 continuity tester 89
Practical in
Power Distribution
12.2 Brief Theory
Every electrical circuit needs four essential elements for proper
functioning, i.e.

(i) Energy source

(ii) Control components like switches, fuses, circuits breaker, etc.

(iii) Wiring

(iv) Equipment or connected load, i.e. lamp, fan, iron, cooler,

heater, etc.

Most of the common faults occur as a result of supply failure, defective

switches, sockets and plugs, faults in the wires, or defective equipment,
and an electrician must understand clearly the reported fault, reason it out
and try to locate it from the simplest possibility.

12.3 Procedure

(i) Note down, the details of the building, flat, house and room
number, if applicable and write down the fault with its
associated circuit such as “Light is not working in room No.
114” or “There is no power in the basement” or “Cooler pump
motor in physics lab. Cooler unserviceable” or “Complete
blackout in the projection room”, etc.

(ii) Take one fault at a time and start the work; try to complete it
before attempting the second one. But if more than one faults
occurs at a time, then attend to them in order of priority, i.e. the
most important first and the least important last. Try to collect
other information related to the faults, which may be helpful in
localizing and rectifying the defect quickly.

For easy understanding, let us take a few typical cases.

 No Electrical Power in a Particular Building

Check if other buildings in the adjoining area have power. If other

building also do not have light, then possibly the mainline (or the
phase) feeding all the affected buildings is off, or a pole fuse or
feeder pillar fuse is blown. Report to the nearest supply agency and
do not attempt any repair.

If all other buildings have power, then check the main fuse in the
main switch, after switching it off.
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 Practical in
(i) Replace the blown fuse with a proper fuse wire of the Power Distribution
specified rating.

(ii) Check the supply at the mains switch with a neon tester
and test lamp. If it is all right, fix the rewired fuse in
position.

(iii) Switch on all loads in the building.

 If the fuse blows out again after switching on the main

switch and other circuits, then proceed as under

(i) Do not attempt to replace the fuse with a thick wire, but
locate and rectify the defective circuit.

(ii) Remove all the fuses from the distribution board, switch
off the circuit switches, and check across each fuse with a
series lamp, i.e. test lamp.

(iii) If the lamp lights on a particular fuse, it shows fault in that

circuit before the switch, i.e. the conductor is earthed to
the conduit or shorted with neutral wire or both. If
rectification is not easily possible, then isolate that circuit,
replace the fuses in the other circuits and switch on. This
fault can be grouped under major rectification.

 In a room, only one light is defective and others are

glowing bright

Sl. No. Possible Faults Rectification

1. Fused lamp Check lamp and replace

2. Lamp loose in the holder Check and replace defective lamp

holder

3. Loose connection at switch Tighten the connection at the switch

terminals terminals

4. Improper switch toggling action Replace the toggle switch with a

new one of same size and rating

5. Loose fuse in holder, blown out Check fuse, tighten contacts and/or
fuse replace the fuse

6. Loose connection at fuse holder Check and tighten the fuse holder
connections

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Power Distribution
 Lights are working but desert cooler/air conditioner
does not work

Sl. No. Possible Faults Rectification

1 Blown out fuse Check and replace the fuse
2 Loose connection at the rear of the Check and tighten connection
3-pin socket
3 Loose connection at the plug pins Open and check the connections in
the plug and tighten the connections,
if required
4 Over heated socket, Oxidized and Replace with a serviceable socket
burnt out pins
5 Low voltage If the lights also glow dim, measure
the voltage, switch off and wait till
voltage improves or use a voltage
regulator
6 Low voltage or repeated fuse Faulty load equipment. Remove the
blow-outs on switching on the load power connection and declare fault.

 In a particular room, no light works, but when

checked, all switches show phase available
When checked with a test lamp, the lamp doesn’t light from the
switches to the neutral wire, but lights to earth.

Possible Fault : Open neutral.

Rectification : check and ensure continuity of neutral return.

12.4 Some common wiring faults in tabular form

Sl. Fault Possible Causes Rectification

No.
1 2 3 4
1. No Light (1) Fused filament lamp (1) Check and replace with
a serviceable lamp
(2) Blown out fuse
(2) Check the fuse and
(3) Defective switch/loose
replace after re-wiring
connections
(3) Check and replace or
(4) Fractured aluminium
tighten connections
wire at the connection
points in holder or (4) Renew connection if
switch fractured
(5) Loose lamp holder (5) Replace with a
serviceable holder
(6) No power
(6) Check for power of
mains fuse, if blown, and
replace
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2. Fuse blows (1) Excess load than (1) Check up the connected Power Distribution
out after planned or low capacity load and remove extra
replacement fuse load, if connected, or put
the proper fuse
(2) Short circuit in the
equipment (2) Switch off and check
each item for earthing
(3) Short circuit exists even and rectify the fault
after disconnection of
the equipment (3) Switch off all load
switches and check
(4) Short circuit exists even
with all the switches in (4) Fault exists before the
the off position switches, locate and
isolate the defective
(5) Short circuit is due to circuit
phase wire short to
neutral inside the (5) Pull out the defective
conduit wire and drew through
new wires and connect
after checking

3. Lights flicker (1) Loose fuse grip in holder (1) Check and replace
when heater in main fuse heating up fuse grip or
is switched main switch, tighten
on (2) Loose contacts in the points in the holder
main switch knife
contacts (2) Check for sparking,
heating up of fuse grip or
(3) Loose connection of main switch, tighten
aluminium conductors in contact points, clean
the main circuit before burn our surface and
distribution ensure the tightness of
connections

4. Water pipes (1) Leakage in wiring (1) Check insulation of wiring

give shock using a megger; if weak,
(2) Open neutral replace the defective wire

(3) Leaking, geyser, oven, (2) Check continuity of

refrigerator and neutral wire
improper or broken earth
return (3) Check all appliances for
insulation and proper
earth return and rectify
the fault 93
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Power Distribution
12.5 Observation Table

Record the observations and actions in a table as given below :

Sl. Location/ Test Reading Observation Result

No. Fault

1 2 3 4 5 6

1. Physics Lab. Continuity Test

No Supply

2. Director’s Insulation Test

room

AC not
working

3.

4.

Note

Only the required tests need be carried out, as relevant to the

reported fault.

12.6 Precautions

 Always switch off mains before testing a circuit or attempting

any repair on the installation.

 Use rubber soled shoes and rubber gloves as far as possible,

while working on electrical installations.

 Use tools with insulated handles.

 While checking with a test lamp, connect one lead first to earth
or neutral and then only connect the second lead to the live
terminal to prevent accidental shock.

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Power Distribution
Self Test Answer the following questions :

Q.1 Describe some common wiring faults with their possible causes and
rectifications.

Q.2 Mention the possible faults and their rectifications in the case of :

(a) No electrical power in a particular building.

(b) In a room only one light is defective and others are

glowing bright.

Q.3 Write the short note on fuse, electrical load, rating of fuse wire and
multimeter.

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