How to add / extend a lighting circuit

To add extra brightness you may need an extra circuit. Please note that this work will need to be notified under Part P of the Building Regulations. If in doubt about any of this, contact a professional Part P registered electrician.

Level of difficulty

Level 2: Intermediate

What you need

  • Fuse holder
  • Wire strippers
  • Screwdriver
  • Screws
  • Hammer
  • Consumer unit
  • Supply terminals
  • Earth cable

The steps to follow

Note:
Existing lighting circuits should serve no more than eight lighting points.
In order to add a new circuit you must either have a spare fuse way or miniature circuit breaker (MCB) available in your fuse box or consumer unit, or you must provide a new second consumer unit which will be wired up in parallel with your existing one. You can do all the circuit wiring back as far as the new consumer unit, but you must call in your local electricity supply company or a qualified electrician to rearrange the mains supply.

  1. Turn off the power at the mains power supply.
  2. Fit a new fuse holder of the correct current rating for the new circuit - 5/6 amps for lighting, 30/32 amps for power and 20, 30/32 or 45 amps for a major appliance (depending on the appliance wattage).
  3. Rearrange the sequence of fuse holders so the highest-rated fuses are closest to the on-off switch.
  4. Next connect in the new circuit cable, connect the live core to the terminal on the new fuse holder and the neutral and earth cores to the corresponding terminals.
  5. Cover the bare earth core with green / yellow PVC cover.
  6. Finish installing the rest of the new circuit wiring and turn on the mains power.
  7. If you need a new consumer unit, consider a unit that will allow for further extensions, rather than cartridge fuses.
  8. Do consider whether to include a Residual Current Device (RCD) - either in the new unit to protect the new circuit(s), or connected into the supply wiring. Consult an electrician for more advice on this type of job.
  9. Mount the new unit close to the existing unit, and fit a service connector box next to it.
  10. Run the new circuit cable(s) back to the new consumer unit. Connect the cable cores following steps 1-7.
  11. Connect the supply terminals of the new consumer unit to the live and neutral terminals of the connector box.
  12. Connect its earth terminal to the house's main earth point with a sheathed earth cable.
  13. Then call in your local electricity company to disconnect the meter tails supplying your existing fuse box, reconnect them to the connector box and fit new tails between the box and the existing fuse box.
  14. Finish installing the new circuit wiring and turn the power on.
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