ICS 29.240.

20
SANS 10198·2:2004
ISBN 0-626-15175-9 Edition 2

SOUTH AFRICAN NATIONAL STANDARD

The selection, handling and installation of

electric power cables of rating not exceeding
33kV

Part 2: Selection of cable type and methods

of installation
 NOTES
1 Scope

This part of SANS 10198 covers criteria to be considered when

an
electric power cable is being selected, and gives a general
introduction to the methods available for the laying of power
cables. It also covers cables that comply with the requirements
of SANS 97,
SANS 1507-1 to SANS 1507-6, SANS 1576, SANS 1339,
SANS 1418-1 and SANS 1418-2.

The induction effects of earth faults in power cables running

parallel to telecommunication circuits are given in annex A.
4 Selection of cable

4.1 General NOTES

An electric power cable has to perform two basic functions:
it has to carry a specified current and it has to withstand the voltage
and fault conditions of the system into which it is connected.
These and other criteria to be considered when a cable is being
chosen are detailed in 4.2 to 4.6.

4.2 Sustained current rating

The following factors might affect the sustained current rating
and are considered in more detail in SANS 10198-4:
a) ambient air temperature;
b) soil temperature;
c) thermal resistivity of the soil;
d) depth of burial; and
e) layout and grouping of cables.

4.3 Allowable voltage drop

4.3.1 Except for extremely long cable runs, the problem of voltage
drop is largely confined to 600/1 000 V cables. Provisions covering
voltage drop are laid down in SANS 10142-1 in respect of asupply
within premises and in the Electricity Act, 1981.{Act No. 41 of1~87),
in respect of supply authorities supplying consumers. In the cassot
industrial and general distribution netwQ~~s, chooselhe size of cable
with due regard to the maximum voltaj;le'dropthat can<~e tolerated.

4.3.2 The maximum length of cable that can carry the rated current
ofthe circuit before the allowableVoltagf1drop is exc~eded increases
with conductor size. The vQltCige drop in 60Q/1 000 V;
cables used to connect squirr~lcage induction rnotorsl0 direct on­
line starters is normally limited'to 2,5% afthe normal Ju II load current
of the motor. FigYfeS} and 2 show the relationship between cable
length and com:tuctorsize when the PElrmilt9d.;.toltage drop along the
cable is limited to 2,5 %. ."

4.3.3~«ample:wittlreference tp figure 1, the smallest copper

conduc,for cablecapcible of carrying a current of 10 A over a length
of 100 m~without exceeding
"::'
a vqltage drop of 2,5 %, is 4 mm'.
-,_.,"_~: <:< S),;!:,'r

4.4 Short-circuit capacity

4.4.1 Under fault conditions, a cable is required to carry currents

many times greater than its normal full load current. The time taken
by the cable's protection system to clear the fault might vary from a
few milliseconds to 3 s. Short-circuit current ratings are given in
SANS 10198-4, and are calculated on the assumption that the heat
resulting from a short-circuit is stored in the conductor and causes an
increase in temperature from the normal maximum operating
temperature to the allowable maximum short time value for the
installation.

4.4.1 cont.I
The short-circuit current rating of a cable can be further limited by the
allowable temperatures of lead-sheathed or armoured wires, and
that of a large size multicore paper-insulatedllead-sheathed cable
can be limited by the current above which bursting can occur. These
limits are indicated on the short-circuit rating graphs given in
SANS 10198-4.

SANS 10198-2:2004
Edition 2

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NOTE 2 MaKirnum condllC':or 7G ·C.
NOTE 3 lV',axirnum
NOTE 4 Ins:ail:mon

Figure 1 Cable CUITent f'ating limited by voltage drop {coppe,conductors)

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NOTE 1 600[1000 muljicore pVC SV'l;'. PVC

NOTE 2. Maximum conductor temperature 70 ·C.
NOTE 3 MaXimum voltage drop 2.5 % at 400 v
NOTE 4 lns;:allation fn air at 30 'C.

Figure 2: Cable current rating limited by voltage drop (aluminium conductors)

4.4.2

Example: consider a 2 MVA 11 kV-380 V transformer which is to be supplied by a paper insulated cable
from a circuit-breaker connected to a system of 500 MVA fault level and having aclearance time of 0,5 s.
The transformer has a normal full load current of 105 A at 11 kV, and reference to the standard rating of
SANS 10198-4 shows that under standard conditions this would be adequately catered for by 35 mmz
paper-insulated cable of belted construction. However, the 500 MVA fault level
demands a short-circuit rating and graphs of SANS 10198-4 show that a 150 mmz paper-insulated cable
would have to be used.

4.5 Mechanical and environmental protection

4.5.1 Cable sheath

4.5.1.1 Extruded solid dielectric-insulated low voltage cables
Extruded solid dielectric-insulated low voltage cables have an extruded sheath which acts as a
bedding for armour when so required.

4.5.1.2 Paper-insulated cables ..

Paper-insulated cables need an impervious metal sheath tQ prevent the ingress of moisture. This
metal is normally either lead, lead alloy or aluminium. Pure lead is sensitive to intercrystalline
fatigue fracture caused by vibration and, under certain conditions, by the effects of thermal cycling.
Consequently, if a lead-sheathed cable is to be subjected;,to moderate vibration, for example near a
road, a railway or heavy machinery, or is to be ,transported over long distance prior to installation,
then a lead alloy E sheath should be specifi~~.,!Where severe vibration is expected, specify a lead
alloy B sheath with single-wire armour. Whetemovement due to load cycling can occur and a
leadsheathed cable is required, give consideration to specifying alloyEor alloy B.
-';>"- --:~.;:

4.5.1.3 Cross-linked polyethylene (~LPE)inSulated cables

XLPE-insulated cables have a foil core screen overwhich is;an extruded sheath that acts as a
bedding for armour when so required.

4.5.2 Armour
4.5.2.1 Single-core cables
When armouring is required on a single-core cable, ensure that the armouring is non-magnetic. A
single layer of a~t:Jminium wire is normally used.

4.5.2..2, MulticorE{tables "1~

One or two I~Yers ofgalvanized steel wire are normally used as mechanical protection for multicore
cables!'especially in mine shafts~
A double layer of steeltap~~issoinetimes used as mechanical protection. Although steel tape
provides some protection against penetration by hand excavating tools, it has insufficient
longitudinal strength to;~ithstand subsidence of the ground or excessive pulling during installation.

I\IOTE:
The conductivity of the earth return path provided by armour wires and lead Sheathing, if present, can
be increased by replacing a number of steel wires with tinned copper wires. Conventionally, sufficient
copper is used to bring the conductance of the earth path to a value of at least half that of the largest
conductor in the cable

~~~~~- Page 6 ----~- . . . ~-. . . - - - - - - ­

4.5.3 Outer protection

The outer protection provided for most types of cable is an extruded PVC sheath. Polyethylene shall
be used when the cable is to be laid by direct burial where water is present, but do not use it indoors or in
ducts where fire hazards may arise. Consider the use of flame-retardant non halogenated compounds
when cables in air are subject to abnormal fire hazards, such as when groups of cables are to be run in
long vertical cableways.

NOTE 1 All plastics are affected by ultraviolet (UV) radiation. The effect of UV radiation can be minimized by
the use of carbon-black loading in the compound.

NOTE 2 PVC can become work-hardened. It should therefore be ensured that PVC-sheathed cables in an
aerial installation are supported on a catenary wire.

NOTE 3 Excessive clamping pressure should be avoided when PVC-she9thed cablesClre cleated.

NOTE 4 PVC is adversely affected by oils and petrol and is attacked b~~nu~ber of chemicals, particularly
the long-chain fatty acids (e.g. those produced by the decomposition of meat and found in abattoirs).

4.6 Interference with telecommunication cables

When an earth fault occurs in a power cable that runs parallel to atelecommunicationcable for some
distance, an induced voltage (which might be of sufficientmagnitudeto endanger human life or even cause
damage to telecommunication equipment or to the telecommunicatioflcable) will appear across the
terminals of the telecommunication cable. The inQuced voltage will depend on whether telephone
transformers or voltage diverters are installed and on the timetaken for toe power system protection to
clear the fault. In the case of Telkom telecon;lmunication cables,'tl1.e maximum allowable induced voltages
are specified by Telkom.A method of calculating the magnitude ofan,·induced voltage is given in annex A.
Induced voltages can be reduced bYil'lPi:easil'lg the separation, and by reducing or eliminating any
parallelism between the power circuitand the telecommunication circuit. When details of a
proposed power cable installation are;spbmitted to TelkomJsee SANS 10198-1), include the
following information:

a) a map or Plansho"';ihg .all~ower cable,routes, except those within buildings;

NOTE Each C3bleroute·shouldbe.numbered for reference purposes.
~::": ' '\' "<,,\>-.~

b) t;ifu/I description bfeach cabl~~ e.g. 6,35/11 kV three-core 95 mm2 copper conductor,
paper insulated, scre~l)ed, lead sheathed, single-wire-armoured and served;

\~gr each cable,the ma:irnum earth fault current that could occur and the total fault
clearance time<fi.e. the relay operating time plus the circuit-breaker clearance time); and
.' CO-',

d) for . eachtabl~l·d~tails of earthing arrangements at the supply end and at the load end of
the cable· ' ;

5 Method of installation
5.1 General provisions

5.1.1 Install cables in such a way as to

a) minimize the likelihood of damage and consequent failure of the distribution system,
b) ensure as far as possible the safety of personnel working in the area in which the cables are
installed, and
c) keep the overall cost of the installation to a minimum.

5.1.2
Where power cables are laid parallel to or across telecommunication cables, comply with the
requirements of Telkom as stated in letters of approval and detailed on marked-up approval plans.
Where alternative methods or installation practices are proposed, obtain approval for.each method
or practice from Telkom before work is begun.

5.1.3
When a cable heats up and cools down due to cyclic changes irl,.19ad, it tehds toexpand and
contract. If the cable is so restrained that this expansion and contraction is prevented (Le. the
installation is a fully restrained system), thermo-mechanical forces will occurwhich, if not contained,
might cause considerable damage to the cable especially at jointpositions.lf expansion and
contraction are allowed to occur, for example by snaking the cable during installation or.by installing
it in cleats or on suitable hangers and allowing it to sag between cleats and hangers (Le. the
installation is an unrestrained system), damage be avOided. Whenever possible, avoid a partly
restrained, partly unrestrained system. . .

5.1.4 When a short-circuit occurs in a distribl,.ltionsystem, all cables. feepIng the fault will, as a
result of the short-circuit currents, be subjected to elec:tromagnetic for~s that will tend to separate
the cores. In a three-core or four-cor~bable'these forces. shall be contained by sheath and armour.
Where three single-core cables are iri$talled in air,. the cables will tend to fly apart. Ensure that
these forces are contained by usiOg trefoil cleats to~nchorthe cables, and by using restraining
bands or straps, usually of stainles~.steel,"between the anchors. Well-compacted backfill in direct
buried installations is normally.sufficiel1t tOl;iontain SUCh forces.

5.2 Outdoor installatio~~,;

5.2.1 Direct burial; .....
When a cable islo be installed outdoors;.bury it directly in the ground wherever possible. Lay the cable in a
trench onacbed cilselected sand or sifted soil of known thermal characteristics and cover it with the same
mat .nsu~e th backflllrnaterial immediately surrounding the cable is well compacted to reduce its
ther . sistance; ... essaryl,;protect the material with concrete or suitable cover tiles. As an additional or
alternativE%precaution, a'brigQtly"coloured plastic warning tape shall be laid above the cable at a depth of at
least 200 mrn below the ground surface. At the ends of a direct-buried section and on either side of a joint
position, the cable should be snaked to minimize the effects of thermo- mechanical forces and ground
subsidence.

5.2.2 In pipes
Where a cable route crosses a road or railway, the cable shall be laid in a pipe to facilitate its replacement
at a later date without disturbing the road surface or railway track. Pipes shall be of any material that will
not collapse in service, and should ideally be set in concrete. Ferrous pipes can be used for multicore
cables but not fur individual single-core a.c. cables.

5.2.3 In Air

---~-'--- ...- - . PageS

Where it is impracticable to install a cable by direct burial (because of rocky terrain, likely subsidence,
the possibility of damage being caused by the later installation of other cables or services), it shall be
installed in air (above ground) provided that:
a) there is adequate support for the cable,
b) the cable is protected from damage that might be caused by road vehicles, mobile cranes,
vandals, etc.,
c) there is free air circulation around the cable, and
d) the cable is shielded from the direct rays of the sun.
Where such provisions are not pOSSible, considerable derating shall have to be applied. Alongside a
railway line or a canal where public access is normally not permitted, a cable shall be installed in
cleats or in J-hangers fixed to suitably spaced posts or to a wall. Install the cable with enough sag between
fixed pOSitions to allow for free cyclic expansion and contraction. Fix single-core cables in trefoil cleats and
strap them at intermediate pOSitions to contain short-circuit forces. A guide tocleat spacing and strapping
is given in SANS 10198-13. Details of installation procedures for aerial bundr~dconductor (ABC) cables
are given in SANS 10198-14. '

5.3 Indoor installations

5.3.1 On cable t r a y s ,
Suitable mechanical protection for cables shall be provided;by ruTll1 ing groupsof cables on purpose made
cable trays or "ladder racks" installed in tiers as necessa(Y:Supports for the trays shallbe free-standing or
fixed to walls; alternatively, roof trusses or joists shall bec~sed as supports. Do no,t fix such supports or the
trays to structural steelwork by means of drilling, as this might weakenlhe structure. Ensure that cable
trays or ladder racks are adequately supported1iatypical spacing for suppoftsbeing 2 m.
Fix multicore cables neatly to the tray by means of clips or straps. Fix single-core cables in trefoil cleats
and strap them at intermediate positions tooohtain short-circuitforces.

5.3.2 In cleats
Individual cables or groups of cables.shall be cleated to walls or to building steelwork.

5.3.3 In conduit or trunking;

Install small single-core catJl~~ supplying llQhting, power points, etc., in conduit or trunking in accordance
with the provisions of SANS1014,?-1.··· ...

5.4 Installatiorlirtcovered
, "',,
C;:lbI
'/2,,,"
eways and service tunnels

5.4.1 Coveredcableways
In coveredcableways that are~too small for free access of personnel, cleat cables to the walls, install them
in hangers oFlay thel'non the of the cableway. When cables are laid on the floor, snake them to allow
for expansion and contraction.

5.4.2 Service tunnels

Service tunnelsthat are provided in power stations and in large industrial complexes may, because of their
size, be equipped with"cable trays. Install the cables as in 5.3.1. Make provision at regular intervals (e.g.
every 50 m) for cable~to cross over from one side of the tunnel to the other, and provide adequate
drainage for the tunnel.

5.5 Installation in vertical or inclined shafts

Ensure that cables installed in vertical or inclined shafts are adequately supported. If the cables are un­
armoured, or are armoured other than with steel wire, provide support at vertical intervals not exceeding
2 m. If steel-wire-armoured cables are used, the vertical support interval shall be increased to not more
than 5 m.
Ensure that the devices used to support the cable are carefully selected and so installed that sufficient
force is applied to grip the outer sheath of the cable firmly, but without any undue crushing of the cable.

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6 Examples

6.1 General
The selection of cables for a typical industrial installation is discussed in examples 6.2 to 6.4
inclusive (see figure 3 below)

6.2 6,35/11 kV cables

The fault level on the 11 kV side of the main supply transformer is 250 MVA. The 11 kV cable "A"
supplying the main switchboard shall be capable of carrying a full load current of 1575 A. For this
rating, a number of single core cables in parallel per phase will be required and the short-circuit
current of 13,1 kA will not be a problem. The radial feed "8" to the 10 MVA tra.n$forl11~r will require a
cable or cables of rating 525 A, and here again the only limitation that has t9 be\consiCliared is the
current r a t i n g . , , " > '
The radial feed "C" to the switchboard supplying the three smaller transformers shall be capable of
carrying 184 A. If it is assumed that this cable is to be direct-buried and standard conditions of
installation apply, a three core PILC belted cable with a 70 mm2copper or 120mlll2aluminium
conductor appears to be suitable. ..••.•
If, however, account is taken of the fault level and clearanceitimaof circuit-breakef<1/3 (250 MVA
for 1,5 s), a 150 mmlcopper or a 240 mmlaluminium cOl'jductorisrequired.
A similar reasoning applies to cable "0" supplying the 2 MVA transformer. The normalfullioad
current of 105 A could be carried by a PILC belted cable \'I(ith a 35 mm2icopper ora 50 mm2
aluminium conductor. The fault level at switchboard 3 will beslightly below'2i50tMVA because of the
impedance of the supply cable but the reducti0n'will be small unless the length' of the cable is
appreciable. If the clearance time of circuit~bfeaker 3/1 is 0,5 s,the minimum conductor size will be
95 mm2copper or 120 mmzaluminium. . .ii i'.
Cables "E" and "F" supplying the 1 MVAaiidQ,5 MVA{transformers are fuse-protected and any fault
on the load side of the fuses will be cleared by the fuses in a few milliseconds. The 12 t let-through
will result in a temperature rise of only~ few degrE;es and can be ignored. These cables shall
therefore be rated according to normalfuH load current requirements, and the smallest cable
available, a 16 mm2 copper or alumit'lium~i;!quivalent,will be adequate even for a ducted installation.
NOTE All of the 6,35/11 kV cablesconsidereda~e could equally have been XLPE or one of the elastomeric
cables. Problems of terminatingslidhc mentterminal boxes designed for PILe cables might, for
the moment, restrict their use in the.sm .'
{_":w

6.3 1,9/3,3 kVcables.

Paper-insulatediPVC-insulated and XLPE insulated cables are available at this voltage. Where the
choice is n.otgoverned by the\):pst of the cable, PVC insulated or XLPE-insulated cables are
generattYpteferredbecause o(~i3se of termination, but a metal sheathed cable might be preferred
when installation is to be by directburial. The fault level at the bars of switchboard 2 is 150 MVA at
3,3 kV (26,2 kA).
The 12 MVA (2, 10 kA)~nd 10 MVA (1,750 kA) connections "G" and "H" to the switchboard should
ideally be busbars but Where this is impracticable, use single-core cables (two or more in parallel
per phase). Paper~jnsulated or XLPE-insulated cables with their higher current-carrying capacity
than PVC-insulated cables will enable three instead of four cables in parallel to be used for the
12 MVA connection and two instead of three cables in parallel for the 10 MVA connection. The fault
rating is not a problem for any of these, but consider the tauIt rating for the outgoing radial feeds
from the switchboard. Cable "J " , for example, which is fed from circuit-breaker 2/1 and is required to
withstand 150 MVA for 0,5 s, should have a minimum conductor size of 185 mm2 copper for PILC or
300 mm2 copper for PVC. If the load on cable "J" were 2 MVA maximum (350 A) and a fused
contactor instead of a circuit-breaker were used so that short-circuit current could be ignored, a
185 mm2conductor PVC-insulated cable could be used. The cables ("K", for example) supplying
high tension motors are fuse-protected and are selected on a current rating basis only. (Voltage
drop is not a problem in this instance).

Page
6.4 600/1 000 V cables

600/1 000 V cables are used in all the low voltage systems currently in operation in the Republic,
the most common being 380 V or 400 V. 500 V or 525 V systems are also found in the mining,
paper and steel industries. At any of these voltages, consider and check the voltage drop before
deciding on cable conductor sizes. Consider also short-circuit current capacity as the fault currents
at these voltages are generally much higher than at high voltage. Consider, for example, the 2 MVA
transformer in figure 3. The short-circuit capacity on the LV side will be 31 MVA (45 kA at 400 V). A
single multicore cable or three single-core PILC cables could not withstand this current. but as three
or more single-core cables per phase will be required to carry the full load current (2,887 kA) and it
can be assumed that the fault current will divide equally between them, the PILC cables shall be
used. Transformers of this size are normally connected by bus bars to thec,ircult~breaker in the main
low voltage distribution board but, where this is impracticable, single-core PVC or P'LC~Qables shall
be used.

NOTE 1 Where the HV side of the transformer is fuse-protected as in the case of thet MVAor 0,5 MVA '
transformer in this example, the cables should be rated simply on a fuilibad current basis..

NOTE 2 Voltage drop is unlikely to be a problem in the cables connecting the transformer terminals to the
main low voltage switchboard, but conducted heat from connected equipment might influence the choice of
conductor size.

The 1 000 A feed "L" from the main dlstributionooard of the 2 MVA transformer is reauired to
withstand system fault current for the time tak,{ilhfor the fault to be cleared. Most mouided case
circuit-breakers and air circuit-breakers withidlrect acting trips willcleara'full short-circuit in 1 to 3
cycles and will provide close overcurrent;.protection; , ';::,;

, _ _ Page
 SANS 10198-2:2004
Edition 2

l Wi" O.S M!/A

11/£1,4 tV i\iO,4 kit
5.5 2: 4,15 %

Figure 3 Typical industrial installation

Three single-core 630 mm2 copper conductor PILC unarmoured cables can carry 1 000 A in air but
under earth fault conditions would suffer from sheath overheating in under 40 ms. In such a case
XLPE-insulated cables would be preferred. Other cables of lower rating (such as "M" in figure 3)
that are supplied through fuses or MC8's shall be selected on a full load current and voltage drop
basis only.
If the full load current of the 400 V motor in the example is, for example, 22 A and the length of
cable UN" is 90 m then, with reference to figure 1, a 10 mm2 copper conductor cable is required.

Page
 NOTES:
Notes to purchasers

A.1 Before the purchaser orders cables produced to this specification, it is

suggested that the following points be considered:
A.1.1 Identification of cores
The identification of cores, particularly in power cables, should preferably be
done by colour coding.ldentification by numbers is also acceptable. The
neutral must always be black or carry the number -O-,or both. Particular care
should be taken to select the correct colours when a three-core or four-core
cable intended for use on single-phase circuits is being ordered.
A.1.2 Current rating
The current rating of the cable and the applicable derating factors for a
particular installation should be ascertained from the cable manufacturer. This
information is also given in SABS 0198-4 and SABS 0142-1.
A.1.3 Type of cable
Careful consideration should be given to the type of cable tClbeusedJor a
particular installation.Alternatives such as copper or alumini~m conductors;
conventional PVC insulation and sheathing;flame-retardant, low smoke
emission, halogen-free cables, armoured or unarmoured cables, etc, should
be c o n s i d e r e d . ' . .
A.2 It is recommended that the following requirements be specified in
invitations to tender and in each order or contract:
a} The maximum permissible operatfngY.olt(ige.
b) The conditions of service ofthe cable ......
c) The conductor material (copper, tinned copper or aluminium) and the
type of conductor. . . ...
d) The type of insulationmateriat:
e) Colour coding or numb .. of cores.
f) The type of bedding ma
g} Whether theGfible is to be armoureq........
h) If the cable~js.to'lbe.armoured,the matetlal.·of the armour wires.
i) In the cas~pf a cabl El with steel wire armour, whether an earth
continuity conductor (EQC) is required.
j) Thetypeof m~terial of tne~heath.
k) Inlthecasepf ac;:able with a.metallic sheath, whether the metal is to
beJead or leat;ialloy oftypeE (see annex B of EN 12548:1999).
I} Wheth.er fire retardal'ltprgperties are required.
m} In the c~$e of cables packed on wooden drums, whether the wood of
the drum is to be resistant to biological attack.
n) Whether the number of cores and the cross-sectional area are to be
indicated on the cable.

A.3
SASS lEe 60332-3 denotes four optional categories, namely A, S, e & D.
Current research indicates that cables that satisfy the requirements for
Category e, comply with the flame propagation requirements for steel wire
armoured cables in accordance with both national and international
standards.

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