How to count cable, conduit and circuits from the points

1. Count the points

List the light points, the sockets and the switches of every room. Flush boxes: one per point.

2. Cable and conduit

Multiply the number of light points by the average cable run per light point, and the same for sockets. Add the waste to get the cable to buy. The conduit is the same run without waste.

3. Circuits and breakers

Divide the light points by the number a circuit takes and round up; do the same for the sockets. The circuits are the sum, with one breaker each.

Worked example: 10 lights, 12 sockets, 6 switches

Average run 8 m per light point and 6 m per socket, 8 points per circuit, 10 % waste:

• Lighting cable: 10 × 8 = 80 m, with waste 88.00 m.
• Socket cable: 12 × 6 = 72 m, with waste 79.20 m. Conduit 152.00 m.
• Boxes: 10 + 12 + 6 = 28.
• Circuits: 10 / 8 → 2, and 12 / 8 → 2, so 4 circuits and 4 breakers.

Cable tray run of 30 m

Bars of 3 m, brackets every 1.5 m, covers, 10 % waste:

• Bars: 30 × 1.10 / 3 = 11.
• Brackets: 30 / 1.5 = 20, plus 1 for the end, so 21.
• Covers: one per bar, so 11.

What this does not cover

The count does not size cables or breakers, check earthing or voltage drop, or apply any regulation. That is the work of a qualified electrician.