Electrical Question

Lighting circuit

I'm having to replace an old 5 amp circuit breaker that fuses a lighting circuit (Upstairs, 5 ceiling lights), while I'm waiting for the replacement to arrive (4-5 days), is it safe to wire both lighting circuits through the other 5 amp circuit breaker? Would be a total a total of 11 lights in all although only 2 maybe 3 would be on at any one time.

2 Answers

Hi. Bit of a difficult one to answer without knowing what kind of consumer unit (fuse board) you have.

If you have a modern fuseboard, with a couple of RCDs, and one lighting breaker is on one RCD and the other lighting breaker is on the other RCD, then you'd need to move the corresponding neutral onto the other RCDs busbar, as well as moving the line conductor to the temp breaker.

If you have no RCDs (which I suspect is the case, else you probably wouldn't have a 5A breaker), or both lighting circuits are on the same RCD, then it might be possible to temporarily move the circuit over - BUT, you need to calculate the total load current of the combined circuits to ensure you don't overload the fuse. You're allowed to use a diversity factor of 66% of total demand if this is a domestic property (90% for small shop, store, office, etc, 75% for small hotel, guest house, etc) in doing the calculation.

If you don't know what diversity factors are, leave well alone and get a competent electrician to do the job for you. Also, old fuse boards are likely to have exposed live parts in them, so there's a significant risk of you electrocuting yourself.

Be safe, get an electrician in.

Answered 28th May 2012

A Brighter Spark

Member since 22 Dec 2011

Yes both circuits connected to one 5amp fuse or circuit is safe, just not ideal.

In reality though due to part P of the building regulations, you should not be carrying out DIY electrical work in the home. - google part P for more information

Answered 28th May 2012

Electrical Safety Services

Member since 17 Oct 2011

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