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Does Size Really Matter For My Electrical Cable?

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In a nutshell the answer is, Yes.

The why takes a bit longer to explain.

The most basic explanation on why wire size (thickness) matters is because the thinner a wire is (higher gauge) the more resistance there will be to the flow of current. More resistance means more energy loss, more energy loss means higher electricity cost, more resistance means more heat, more heat increases the chances of wire failure and combustion.

A practical example:

Straton Electrical was recently asked to inspect a home which had a prepaid meter installed. The owner of the home stays in the flatlet and rents the main house out to tenants. The owner could not understand why her tenants were consuming LESS electricity than she was.

Upon inspection we noticed that the cable coming off of her 40 Amp Circuit Breaker feeding the flatlet was connected with a 2.5mm cable. This size cable is rated for a 15 Amp supply and not a 40 Amp supply which should be a 6mm cable.

BUT – at the flatlet sub Distribution Board the cable coming in was the proper size cable.

Closer inspection in the roof revealed that the proper cable had been spliced with the thinner cable AND other plug circuits in the home were also running off of this cable.

Why is this wrong:

  1. The owner (in the flatlet) was paying for the tenant’s consumption
  2. The incorrectly connected plugs should be on a 15 Amp circuit breaker and NOT a 40 Amp Circuit Breaker
  3. The cable is far too thin to handle all that load and a fire hazard.

When making any changes to your electrical installation in your home you need to insist on an addendum to your electrical certificate – this may cost you a few rand more BUT will be well worth it for peace of mind and the possibility of your insurance company refusing to cover your home in the event of a fire.

The South African National Standards (SANS) covers all aspects of an electrical installation.

Specifically these codes are applicable in the above case:

  • SANS 1507 Low Voltage PVC and XLPE insulated cables. Includes armoured cables.
  • SANS 1574 Flexible cores and cables, including panel wire, cabtyre and ripcord.
  • SANS 1418 LV Aerial Bundled Conductors.
  • SANS 1520 Rubber insulated cables. Parts 1 and 2 cover LV and MV respectively.
  • SANS 97 Paper Insulated Lead Covered cables up to 33 k V.
  • SANS 1339 XLPE insulated cables up to 33 kV.SANS 182 Overhead line conductors.

There are many others, but the above being the most commonly used

Brought to you by Straton Electrical – for all your electrical contracting, maintenance and repair needs.

Get a quick run down of what size inverter you will need to keep YOUR lights on here: What Size Inverter do I need for Loadshedding?.

For more info see the Safehouse Guide to Electric Cables.

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Michael Straton

Devoted Father, Long Suffering Brother, Gifted Electrician, Kind Human Being. I spend a LOT of TIME at Straton Electrical.