I have recently started some work in my loft and found that the lighting circuit is a ring (from consumer unit via lights and back to the consumer unit). On checking the circuit there are 1400 watts of lighting and the cable is 1.5mm2. Has anyone seen this before and is it OK/safe.
Lighting Circuit, is it safe?
- Thread starter Gazp
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does it start / end at same mcb / fuse?
I think that it might be a mistake the partially-educated amateur makes, when he has had Ring Finals (for sockets) explained to him and not grasped why lights do not need to be done that way. I once thought that, until it was explained to me (never installed one like that, though).
Yes it returns to the same MCP which is rated at 16Amps. I was under the impression that lighting circuits were meant to be radial circuits. Also isn't a 6Amp rated MCP more usual, or has this been uprated as the power is over 1200 Watts?
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Gazp said:
That is wrong. Yes, they should be radials. It should be 6Amp* which will support the load you mentioned earlier.
OOI, that is quite a high lighting load - is it a domestic house; and what sort of lamps have you got? Is it one circuit per floor, or one per house?
*Yes, I know.
a 1400w load will draw about 5.8A. it could still be protected with a 6A MCB.
If you have one lighting circuit for the whole house, i'd suggest splitting the circuits and having two 6A breakers - one for the downstairs lights and one for the upstairs lights - and it might be an advantage to have one light at the top of your stairs/landing area which is controled/wired in with the downstairs circuit - so's if your upstairs breaker trips for any reason you can still see to get downstairs to go sort the problem.
thats presuming you live in a 2 storey house and your CU is downstairs! - im presuming a little i know!
If you have one lighting circuit for the whole house, i'd suggest splitting the circuits and having two 6A breakers - one for the downstairs lights and one for the upstairs lights - and it might be an advantage to have one light at the top of your stairs/landing area which is controled/wired in with the downstairs circuit - so's if your upstairs breaker trips for any reason you can still see to get downstairs to go sort the problem.
thats presuming you live in a 2 storey house and your CU is downstairs! - im presuming a little i know!
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BTW, 1,5 can also be used with 10A breaker.
There`s nothing to forbid forming a ring final on the lighting circuit providing all the installation conforms to relavant standards, although it is pretty unconventional.
I know of one electrician who actually used to do this.
I have seen an installation where the lighting was "ringed" but fed off two seperate MCBs (potentially lethal).
I am wondering if a proper Periodic Inspection of all your wiring might throw up other defects.
I know of one electrician who actually used to do this.
I have seen an installation where the lighting was "ringed" but fed off two seperate MCBs (potentially lethal).
I am wondering if a proper Periodic Inspection of all your wiring might throw up other defects.
(Please note increasing the fuse rating of a circuit should only ever be carried out by an electrically competent person.) A lighting circuit with BC / ES lampholders can be fused up to 16A, 1.5mm twin and earth is rated at 20A for clipped direct before correction factors. iirc SES and SBC lampholders must not be fused above 6A.
My post wasn't aimed at you JohnD, it was aimed to clarify to the DIYers out there that although it can be done it needs to be done by someone who is competent to do it, fusing a lighting circuit to 10A or 16A involves carefull consideration as to what the loading is and what it may be changed to by the DIYer in the future, not to mention efli and the likes which most DIYers will most likely never heard of.
Gazp said:
little confused by this, I understand radial to be a seperate cable toeach light from the consumer unit.
All lighting I have seen has been from consumer unit, to 1st light, then 2nd, then 3rd etc etc.
Just wanted to get some clarification on this so that I can confim if I understand it correctly.
Also I thought it was ok to go over the 1380w as its a reasonable assumption that not all lights will be siwtch on all at once, is this correct?
waynes said:
You would call those radials, but that method (one radial circuit per load) is used for higher-amperage things than domestic lamps. For example, an electric cooker, or an immersion heater, is connected that way
waynes said:
Yes, that is the normal way to do a lighting circuit. Each of the lamps is very low load.
waynes said:
Yes, that's right, a 6A MCB will support about 1380 of lighting all on at the same time (which is actually quite a lot) and rather more than that for brief periods. However, these days, most people have a lighting circuit per floor of their house, and some compact fluorescents, very few have 14 x 100W lamps per floor, so diversity does not usually need to be applied.
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