About this calculator
Work out how much Surfix cable to buy for plug and light points, in the right size for the circuit breakers, rounded to the 10, 50 and 100 m lengths it is sold in.
How it’s calculated
Cable = number of points × the average cable length per point, measured on your plan from the distribution board, plus waste. The conductor size follows SANS 10142-1 table 6.27, which gives the largest breaker each small conductor may be protected by: 10 A for 1 mm², 16 A for 1.5 mm² and 25 A for 2.5 mm². So 1.5 mm² Surfix suits 10 A and 16 A circuits, and 2.5 mm² suits 20 A plug circuits.
SANS 10142-1 doesn’t limit how many points a circuit may have, but a plug circuit’s anticipated load may not exceed 5 kW, and only circuits on a breaker of 20 A or less may mix plugs, lights and fixed appliances. Surfix twin and earth is sold in 10, 50 and 100 m lengths.
Worked example
With these inputs:
- Plug points
- 12
- Light points
- 10
- Average cable per point (measure on your plan)
- 6 m
- Plug circuit breaker
- 20 A
- Light circuit breaker
- 10 A
- Waste allowance
- 10%
the result is:
- Surfix cable
- 145 m
- Plug circuits (20 A)
- 79 m of 2.5 mm²
- Light circuits (10 A)
- 66 m of 1.5 mm²
Tips from the trade
- Run stoves, geysers and aircons on their own circuits sized for those appliances.
- Keep plug and light circuits separate where you can, so a tripped plug doesn’t leave the room dark.
- Plan the cable routes before you chase walls, so you know the real run lengths.
Common questions
What size Surfix for plugs?
2.5 mm² for a 20 A plug circuit: SANS 10142-1 table 6.27 allows 2.5 mm² on breakers up to 25 A and 1.5 mm² up to 16 A.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and SANS 10400 (the National Building Regulations) and your local municipality before ordering.