INFORMATION SHEET 1.
PEC PROVISION ON ELECTRICAL METALLIC TUBING
INTRODUCTION
A rigid metal conduit is a type of wiring installation which is designed to
lessen or eliminate fire hazard and electrical accident. The following rules and
regulations on the use of electrical metallic tubing should be observed:
A. Application
Electrical metallic tubing may be used for exposed and concealed work at
the same condition with rigid metal conduit. EMT protected with enamel
should not be used on the following conditions:
a. subjected to mechanical during or after the construction
b. Cinder fill
c. hazardous location
d. exposure to corrosive fumes and vapor
B. Sizes
Electrical metallic tubing has smooth surface inside diameter. Its standard
length follows the gas pipe which is 10 ft. and a diameter from ½ inch, ¾ inch
up to 6 inches.
C. Location of some corrosive fumes and vapor
a. meat packing plant
b. tanneries
c. salt storage plant
D. Under wet location
Electrical metallic tubing can be used provided the water is prevented in
entering the conduit. The support, straps and other fitting must be approved
for the purpose.
E. Number of conductors in tubing
The number of conductor for every single run of EMT should follow the
given table on the next page:
Trade size of conduit in inches Size in AWG No. of conductors
3/8” 16 8
1/2" 14 8
3/4" 12 10
1” 6 12
1 ½” 2 12
(Reference: Interior and Exterior Wiring and Troubleshooting, pp. 135-136 by Feliciano Agpaoa)
F. Assembly
Thread less coupling and connectors used with tubing should be tight and
should be provided with waterproof type fitting if will be used in wet location.
G. Types of EMT fitting (Reference: Interior and Exterior Wiring, pp. 137-138 by Feliciano
Agpaoa)
Connector Coupling Adapter
Locknut Elbow Condulets
H. Type of EMT utility boxes and fitting
Utility Box Octagonal Box Clamps/Straps
I. Number of bends of EMT
The code requires a maximum of four adapter bends (360) for every one
run of tubing.
J. Types of bends
The following illustrations show the different kinds of bends used in the
installation of electrical metallic tubing.
Obstacle
Elbow bend 90 Offset bend Saddle bend
K. Personal Protective Equipment (PPE)
Goggles Helmet Gloves
INFORMATION SHEET 2.1
INSTALL RIGID METALLIC CONDUIT (RMC)
INTRODUCTION
A rigid metal conduit served the same
purpose as with the Electrical Metallic
Tubing. They are designed to protect the
electrical wiring of building from electrical
hazard due to faulty wiring. It is usually
installed buried in concrete wall floor and
ceiling, in masonry or similar materials. It
is also used for exposed and concealed
works, it provides maximum protection
due to mechanical damage. In order that this wiring method will become
effective, safe and reliable, it is a must that it should follow the PEC standard
and specifications.
PEC provisions
The Philippine Electrical Code is a set of rules and regulations which govern
all electrical wiring. The following standard and specifications must be followed
in installing Rigid Metal Conduit:
Standard size of RMC
Rigid metal conduit has smooth inside diameter. Its standard length follows
the gas pipe which is 10 feet and a diameter from ½, ¾ , up to 6 inches.
Installation under atmospheric condition
Protected by Enamel- Conduit protected only with enamel are permitted
only in indoor occupancies not subjected to severe corrosive influences.
Dissimilar metal – Contacts of metal to another metal must be avoided
in installing RMC to prevent the possibility of galvanic reaction.
Corrosion protection – Conduits fitting with corrosion protection are
permitted to be installed in concrete, direct earth burial or in areas
subjected to corrosive influences.
Number of conductors inside the conduit
The table on the next page shows the number of conductors permitted in a
single conduit.
Maximum number of conductors allowed in trade size conduit from ½ - 3 inches.
Conduit
½ ¾ 1 1¼ 1½ 2 2½ 3
trade size
Conducto
Type letter
r size
TW, XHHW 14 9 15 25 44 60 99 142
12 7 12 19 35 47 78 111 171
10 5 9 15 26 36 60 85 131
8 2 4 7 12 17 28 40 62
RHW, 14 6 10 16 29 40 65 93 143
RHH,THW 12 4 8 13 24 32 53 76 117
10 4 6 11 19 26 42 61 95
8 1 3 5 10 13 22 32 49
TW,THW,RH 6 1 2 4 7 10 16 23 36
W 4 1 1 3 5 7 12 17 27
RHH(without 3 1 1 2 4 5 10 15 23
covering 2 1 1 2 4 5 9 13 20
1 1 1 3 4 6 9 14
Fittings
The following are type of conduit fittings which are usually used when
wiring installation make sharp turns. The letter shows that an elbow or fitting
makes right angle turn. They are:
LR LB
LL C
Bends
Rigid metal conduit can also be bent using hickey or conduit bender. It
follows the same procedure bending electrical metallic tubing.
Bending RMC using hickey Hickey
Cut
Conduit is cut with hacksaw or pipe cutter. For easy and safe way of cutting, a
bench vise is recommended so that pipe can be held firmly while it is being cut.
Cutting pipe using hacksaw Pipe cutter
Ream
After cutting the pipe with hacksaw or pipe cutter, it leaves burrs. This
must be removed to avoid damage of wire insulation when it is inserted in it. A
reamer or round file can be used to remove burrs.
Threads
Since rigid metal conduit is commonly used in places where there is wet
location, sealing of termination can be best done if pipe is treaded. These will
prevent water from entering the conduit. The use of dies and dies stock keep
the end of the pipe threaded. The sizes of dies stock ranges from ½ to 6 inches.
Dies and dies stock Tripod w\ pipe cutter Die and dies stock set
