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The SAFEhouse Guide

Electric Cables
Electric cable
The purpose of electric cable is to convey electrical actual conditions of installation, in particular: ambient
energy from the point where it is available to a point air temperature; presence of solar radiation; number of
where it is required. In order to do this safely and reliably, cables and their spacing from each other; depth of cable
the cable needs certain attributes. laying; ground thermal resistivity; etc.
1. The voltage rating of the cable must be equal to, or Standard conductor sizes are: 1,5 mm2; 2,5 mm2; 4
greater than, the voltage rating of the system into mm2; 6 mm2; 10 mm2; 16 mm2; 25 mm2; 35 mm2; 50
which it is connected. mm2; 70 mm2; 95 mm2; 120 mm2; 150 mm2; 185 mm2;
2. The current carrying capacity of the cable must be 240 mm2; 300 mm2; 400 mm2; 500 mm2; 630 mm2;
equal to, or greater than, the current to be carried, 800 mm2; 1 000 mm2; 1 600 mm2; 2 000 mm2; and 2
taking into account any applicable current de-rating 500 mm2.
factors.
3. The short circuit and earth fault rating of the cable Short circuit rating
must be greater than the prospective short circuit The short circuit rating of any conductor can be calcu-
and earth fault currents that the electrical system may lated by referencing manufacturers’ brochures. Alter-
impose on the cable. natively, the value can be calculated by multiplying the
4. The cable must be compatible with, and able to cross-sectional area of the conductor by the appropriate
withstand, the environmental conditions in which it is factor, which yields the one second short circuit rating.
installed. 1. The factors for MV cross-linked polyethylene (XLPE)
5. Special attention must be paid to contributing factors cable are:
such as cable voltage drop and the nature of the
• Copper conductor: 143 A/mm2.
supplied load.
• Aluminium conductor: 92 A/mm2.
Cables are made for the following
voltages. 300/500 V; 600/1 000 V; 1,9/3,3 kV; 3,8/6,6 kV; 2. The factors for paper insulated lead covered (PILC)
6,35/11 kV; 8,7/15 kV; 12,7/22 kV and 19/33 kV; as well as MV cables and LV polyvinyl chloride (PVC) insulated
high voltage cables from 44 kV to 275 kV. cables are:
• Copper conductor: 115 A/mm2.
Voltage rating
• Aluminium conductors: 76 A/mm2.
The first of the two numbers is the phase-to-earth rating,
and the second number is the phase-to-phase voltage Actual figures for any particular conductor size and fault
rating. Both 300/500 V and 600/1 000 V cables are the duration are available from manufacturers’ brochures.
voltage ratings typically used in the wiring of domestic
and small commercial installations.
Earth fault rating
Municipalities and industry primarily use 6,35/11 kV
cables for the distribution of electricity. The other higher The earth fault rating of an electrical cable may also be
voltage ratings mentioned are less common. obtained from manufacturers’ brochures or calculated.
When calculated, the value is obtained by multiplying the
cross-sectional area
Current rating of the earth path by the appropriate factor. The factors
Electric cable manufacturers publish tables of current are
ratings applicable to the size and type of cables they 24 A/mm2 for lead sheath on PILC cables and 143 A/
manufacture. Different current ratings apply for cables, mm2 for copper tape screen on MV XLPE cables.
depending on the size of the conductor, and whether the Actual figures are available from manufacturers’
cable is installed underground, in free air, or in ducts. brochures.
These ‘standard’ current ratings must be modified for
each unique installation by taking into account the
 The SAFEhouse Guide
Electric Cables
Electric cable components

Conductor is to be installed underwater or in marshy land, medium

density polyethylene (MDPE) is often specified because
The conductor carries the current, and must be of of its superior radial water blocking advantages and its
a sufficiently large cross-sectional area to avoid the toughness.
conductor overheating. The conductor may be solid
circular, stranded circular, solid shaped or stranded
shaped, depending on the cable specification to which Marking
it was manufactured. Copper and aluminium are metals All national and international electric cable specifications
with good electrical conductivity and this, together with call for certain markings on the cable outer sheath. At the
other favourable attributes, makes them ideal for use in very least, this should include the manufacturer’s name;
electric cables. These are the only materials specified the specification to which the cable is manufactured;
for conductors in South African cable specifications. The a description that includes the number of cores; and
conductors are critical components within the cable. the voltage rating of the cable. Where large orders are
Conductors are available with water blocking. negotiated with the manufacturer, it is possible to include
conductor size and even metre-by-metre marking along
Insulation the length of the cable. Sometimes the cable marking
may include ‘Property of ...’ or a contact number to assist
The insulation around the conductors must exhibit high in the event of the cable being stolen. On request, unique
resistivity to withstand the applied voltage. It must also be conductor markings can be printed on cables that carry a
able to withstand relatively high conductor temperatures risk of theft.
before becoming soft or melting. In addition, it must
be capable of being applied to the conductors using In many respects, the outer sheath is the most important
extrusion technology (paper cables are lapped not component of the cable. It keeps water out of the cable,
extruded). Insulation is an important component of thereby assuring a longer life span and fewer problems
electric cable and determines the cable’s lifetime. during operation.

Bedding
Certain cable constructions require a layer of bedding
under the armour layer. Its purpose is to protect
the underlying components during the armouring
application by providing a soft layer on which the
armour can be applied without damaging the underlying
cable components. It is probably the least important
component within the cable, but its thickness and Conductor
material quality are nevertheless stipulated in the cable
specifications. Normally PVC with fire retardant properties
are used. Insulation

Armouring Bedding
Armouring may consist of steel wire armour (SWA),
Armouring
aluminium wire armour (AWA), or steel tape armour.
Galvanised steel wire has many advantages over steel
tape and is most commonly used. The armour minimises
damage to and protects the underlying components from
external impact. Importantly, SWA provides the cable Outer sheath
with better tensile strength, which is important if ground
movement is likely to occur.

Outer sheath
Markings
The cable outer sheath protects it from ingress of
moisture and provides overall mechanical protection:
weather, chemical and electrical. PVC is commonly used
and is satisfactory for most applications. Where the cable
 The SAFEhouse Guide
Electric Cables
Different types of low voltage electric cable

Low friction single-core general cable/housewire. Surfix.

PVC single-core flexible panel wiring cable. Submersible pump cable green (four-core)

HRQ high temperature insulated wire Submersible pump cable blue (three-core)
(105 ⁰C) cable.

Cabtyre flexible cable. Nitrile trailing cable.

Audio flexible cable (ripcord). PVC nitrile welding cable.

Illumination flexible wiring cable (Maconite).

EPM/CM or EPM/CR welding cable.

PVC single-core general purpose housewire.

Low voltage three- and four-core SWA cable.

Flat twin and earth.

Who polices the electric cable

Standard cable installations
industry in South Africa?

The Association of Electric Cable Manufacturers of South

Africa (AECMSA) represents the interests of consumers
and manufacturers.
The South African Bureau of Standards (SABS)
and sets the National Standards and also operates
a voluntary product certification scheme for these
Cable in trench Cable in sleeve/pipe products, which ensures continued compliance of
SABS certified products. The National Regulator for
Compulsory Specifications (NRCS) sets local compulsory
Cable on ladder specifications for some cable types and carries our
market surveillance inspections to monitor compliance..
The policing of standards was not being carried out
effectively and this led to the formation of SAFEhouse
to ensure that products supplied in South Africa comply
with applicable standards.
 The SAFEhouse Guide
Electric Cables
Compulsory specifications for
South African electric cable

SANS 1507: Low voltage PVC and XLPE insulated cables

What to look for when buying cable
(includes armoured cables).
• Does the cable carry the SABS mark? Is a SANS
SANS 1574: Flexible cores, cords and cables, including panel
standard indicated on the cable?
wire, cabtyre and ripcord.
• Is the manufacturer’s name on the cable? Do you
SANS 1418: LV aerial bundled conductors.
recognise the manufacturer’s name?
SANS 1520: Rubber insulated cables. Parts 1 and 2 cover LV
• Is the SAFEhouse logo on the packaging?
and MV respectively.
• Does a visual inspection of the cable reveal defects
SANS 97: Paper-insulated metal sheathed cables up to 33 kV.
such as inconsistent radials, rough surfaces, bulges
SANS 1339: XLPE insulated cables up to 33 kV. on the sheath, and other irregularities that are a
cause for concern?
SANS 182: Overhead line conductors.
• Does the cable contain copper coated steel in the
There are many other specifications, however the above are
conductor? As copper is not magnetic, a simple test
most commonly used.
using a magnet can reveal the presence of steel.
SANS 1576: Welding cable (voltage rating 100 V) is not compul-
• Does the cable feel too light for its diameter or does
sory.
the price of the cable seem ‘too good to be true’?
This is more common in cabtyre (extension leads)
Other locally manufactured when copper clad aluminium has been used.
electric cable products
Examples of substandard cables being sold in
This brochure covers only some of the low voltage electric
cable products. Reputable local manufacturers make a full South Africa
range of low voltage, medium voltage and high voltage cables Copper coated aluminium and steel passed off as pure
and copper: Typically cable size corresponds approximately to the
accessories, which include: measured physical cross-sectional area, but the resistance
• 1.9/3.3 kV three-phase four-wire low cost cable. would be much higher. The cross-sectional area is only nominal
• House service connection cable. and the important property associated with a particular size is
its electrical resistance, on which its current rating is based.
• Silicone rubber insulated cabtyre and other cables. For example, it is not necessary for a 2,5 mm² cable to have a
• Ranges of fire performance cables. physical cross-sectional area of 2,5 mm², but it is essential that
• Aerial bundled conductors (ABC) rated from 600/1 its electrical resistance does not exceed 13,3 Ω/km at 20 °C.
000 V up to 19/33 kV. Alloys, such as brass, used instead of pure copper: This is
• Rubber insulated flexible trailing cables from 300/500 important for the same reasons as above. Also the cables can
V end up being much stiffer, making some domestic jointing
up to 19/33 kV.
practices in common use in South Africa quite dangerous.
• Overhead lines, including ACSR, AAC, AAAC.
Incorrect size: This has not yet been seen in South Africa
• Medium voltage paper insulated and lead covered but we should be aware of it. In countries where there is little
cables (PILC).
control, it has been found that cables are marked one size
• Medium voltage cross-linked polyethylene (XLPE) bigger than they actually are. The sting in the tail is that any
insulated cables. supplier who chooses to actually supply the correct sized cable
• High voltage XLPE cables (44 kV to 275 kV up to 2 is priced out of the market, so the situation persists.
500 m2).
Undersized insulation radials: With low voltage cables,
• Renewable energy (Solarflex) cables. including flexible cables, the dielectric properties of the insu-
• Locomotive and rolling stock rail cables. lation are not as important as the physical separation
• Anti-theft cable solutions. they create between live conductors and their surround-
ings. This is because the electrical stress that the
insulation is subjected to is usually much lower than the
material is capable of withstanding. However, a thinner
 The SAFEhouse Guide
Electric Cables

radial is more likely to be damaged during normal domestic use, exposing users to the possibility of electrocution or
fire.
Cheap insulation compounds: Most small cables for domestic use are insulated with PVC-based compounds. PVC
readily accepts fillers and additives required for properties such as flexibility, insulation resistance, UV-resistance, and
colour. However, unscrupulous manufacturers cheapen products by increasing filler loadings, resulting in a loss of
physical and electrical properties. Be aware of insulation that strips too easily or that becomes brittle when exposed to
sunlight.
Cable sheaths: The sheaths of cables for domestic use are usually made from PVC compounds and physically
protect the cable cores; however, as sheaths are made to slightly different standards, they can also be cheapened
detrimentally.
 The SAFEhouse Guide
Electric Cables
The South African SAFEhouse Association is an independent, registered, non-profit organisation established by the
electrical industry and committed to communicating with customers.
SAFEhouse has been established to combat the proliferation of dangerous products and services by making the
market aware of the risks in using such products and services, exposing sub-standard products and services, and
persuading specifiers, suppliers and distribution channels not to recommend or to offer such products and services
for sale.
SAFEhouse members have signed a code of conduct that
commits them to dealing only in safe electrical products and to responsible behaviour.
If you have doubts about a particular product or service,
contact SAFEhouse for guidance.

No portion of this publication may be reproduced, copied or transmitted save with written permission of the SAFEhouse Association.

While every care has been taken in compiling the information contained in this guide, neither the SAFEhouse Association nor the publisher can accept any
responsibility for any errors or omissions herein.

For a list of reputable local manufacturers or for technical information

on these products, please contact:

+27 11 396-8140 info@safehousesa.co.za www.safehousesa.co.za