ELECTRICITY MADE SIMPLE 5: CHOICE OF CABLES 2


 

 

We now know that cables and wires are mostly made with copper and aluminum materials. In this section, we shall focus on copper wires, the most widely used in house wiring, know some types of wires and examine the reasons for selections of those wires in house wiring. Most of the guidelines given below are for general applications as a guide; the qualified Electrical Engineer/Technicians must be consulted when big electrical installation work is to be carried out.

 

Let us quickly clear a well known confusion of using wire and cable interchangeably: when you are referring to a single conductor whether coated or not, it is called WIRE. It is still also called wire if the conductor is more than one, but without insulation.

Once you have more than one conductor together and insulated (covered) for example, with PVC, then it is called CABLE.

 

Some of us who may have built a house before may have heard statements like “1mm” or “2.5mm” wire and so on from our local electricians. What they are actually saying for the 2 examples mentioned above are: 1mm2 (1 millimeter squared) and 2.5mm2 wire, which actually describes the cross-sectional area of the wire.

cable3

 

Cross-sectional area of conductor

As seen above, we are concerned about how “thick” a wire is because, the current carrying capacity of a copper cable (and indeed all materials) is directly proportional to its cross-sectional area. In simple language, the thicker the wire the higher the current it can carry conveniently without endangering the life of the user.

 

The mm2 is the metric form of specifying cables, as commonly used in commonwealth; indeed there are others like AWG-American Wire Gauge, SWGImperial Standard Wire Gauge and so on. There are methods to convert from one form to the other, which is outside our scope. We shall continue with metric for this write-up.

 

The common types of copper wires available in Nigeria are noted in sizes as follows:

0.8 mm2 single core or stranded

1 mm2 single core or stranded

1.5 mm2 single core or stranded

2.5 mm2 single core or stranded

4 mm2 single core or stranded

6 mm2 single core or stranded

10 mm2 single core or stranded

 

And so on

 

For cables we have:

1.5 mm2 two (or 3, 4) core or stranded

2.5 mm2 two (or 3, 4) core or stranded

4 mm2 two (or 3, 4) core or stranded

 

And so on.

cable4

 

A number of factors, such as voltage drops, length, operating temperatures, fittings and appliances to be used, types of electrifications, whether conduit, halve conduit or surface and so on affects the choice of wires/cables recommended by the Engineer/Technician for a particular building under consideration.

 

There is however a general rule of the thumb that to get the current carrying capacity of a cable, you can just multiply the cross-sectional area by 4 for copper wire.

 

But to help readers get informed, I have used available catalogue from different sources, to form the table below, which is adequate to serve as a guide for all wires and cables, required for all equipment and appliances used in domestic buildings:

 

NO Cross-Sectional Area (mm2) Current Carrying Capacity (Amps) Applications
1 1 11 Lightning points
2 1.5 13 Lightning points, Ceiling fans and so on
3 2.5 16 Sockets for main house appliances such as TVs, stereo, fridges, freezers and so on
4 4 21 Small (1Airconditioners, small cookers, water heaters e.t.c
5 6 28 Water heaters/Cookers
6 10 34 DOMESTIC Central air conditioners & Electric Cooker

 

 

WARNING:

If you use a lower rated wire or cable for appliances that consumes higher current, the copper will heat up, burn the PVC (insulator), which may lead to bridging of the wires and eventually fire.

cable4

 

This is the major cause of house fire/burning related to electricity.

 

NEXT:

We shall explore the types of wires and cables in the Nigerian market and learn how to identify fake and unsuitable cables for our use. We shall expose original “Nigerian Cables”

 

©Tunde Y. Salihu, 2017

234-803 324 6068

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