How much can a lighting circuit take?

Hi,

I'm in the process of redesigning my bathrooms upstairs and would like a few luxuries that would have to be powered from the lighting circuit.

At the moment everything has been transferred over to LED so I've only got around 100W of bulbs on the upstairs lighting circuit (6A breaker). Also on that circuit are a couple of extractors and security cameras (about 50w total).

I'd like to add some ceiling speakers run by a 250W amp and some underfloor heating which would come in at another 800W. I know this comes in under 6A but is it good practice and if so/not which part of the regulations apply.

Cheers

Traditionally a lighting circuit was limited to 1200W in the days of 240V and 5amp circuits and all that.

It's still something like that, around 1380W.

You wouldn't normally put underfloor heating on a lighting circuit, it's just not done.

I suspect there will be a way of putting the ufh on the socket circuit.

BS 7671:2008 said:

314 DIVISION OF INSTALLATION
314.1 Every installation shall be divided into circuits, as necessary, to:
(i) avoid hazards and minimize inconvenience in the event of a fault
(ii) facilitate safe inspection, testing and maintenance (see also Section 537)
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation
(v) mitigate the effects of electromagnetic interferences (EMI)
(vi) prevent the indirect energizing of a circuit intended to be isolated.
314.2 Separate circuits shall be provided for parts of the installation which need to be separately controlled, in such a way that those circuits are not affected by the failure of other circuits, and due account shall be taken of the consequences of the operation of any single protective device.
314.3 The number of final circuits required. and the number of points supplied by any final circuit, shall be such as to facilitate compliance with the requirements of Chapter 43 for overcurrent protection, Section 537 for isolation and switching and Chapter 52 as regards current-carrying capacities of conductors.
314.4 Where an installation comprises more than one final circuit, each final circuit shall be connected to a separate way in a distribution board. The wiring of each final circuit shall be electrically separate from that of every other final circuit, so as to prevent the indirect energizing of a final circuit intended to be isolated.

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So that is the regulation, the main point is (iii) and as pointed out many times, if there is a general power failure clearly the lights fail anyway. So you can't remove the danger completely you just have to take account of the danger. Personally I think I did not really comply with the above when I fitted 2 RCD's for the whole of the house, and when I moved I fitted 14 instead. But it is not cut and dried, you have to decide as the designer if what your going to do is reasonable, personally I would say it's not reasonable, but that's a personal opinion.

ericmark said:

So that is the regulation, the main point is (iii) and as pointed out many times, if there is a general power failure clearly the lights fail anyway. So you can't remove the danger completely you just have to take account of the danger. Personally I think I did not really comply with the above when I fitted 2 RCD's for the whole of the house

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Whilst I think I know what you're trying to say, I don't think that (iii) of that regulation is the issue, since what that says is:

(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit

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... and having multiple RCDs, and having one lighting circuit supplied by it's own RCD/RCBO does not address that issue (as written) at all. As far as I can see, the only thing one could do to "take account of danger that may arise from the failure of a single circuit such as a lighting circuit" would be for every room to have lights fed by at least two different lighting circuits (and fed from different RCDs/RCBOs) - and, as you say, even that would not help in the face of a power cut.

As for 314.1(iii), I think that you (and most others) have probably read that reg as if it says something like:


... but that is NOT what (as written) it says.

Kind Regards, John

Thanks for the info. I've started re-tiling the splash-back in the kitchen below the bathroom. When I've taken off the old tiles I can see the power cable to the kitchen extractor that comes from a fused spur. Can I use a WagoBox to run a 2.5mm wire from this cable, to a fused spur above the cabinets, which then supplies the heated floor in the bathroom above?

sparkwright said:

Traditionally a lighting circuit was limited to 1200W in the days of 240V and 5amp circuits and all that.

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And "100 watts per point or actual load if greater" so the fact that most are now LED would be ignored.

Is 250 watts for the amp the audio output or the power input? If the amp is for the kitchen I'd probably put it on the kitchen fan circuit, but not if it's elsewhere.

Definately not the underfloor heating on a lighting circuit, and I'd be reticent about putting it on kitchen fan spur either.

ericmark said:

So that is the regulation, the main point is (iii) and as pointed out many times, if there is a general power failure clearly the lights fail anyway. So you can't remove the danger completely you just have to take account of the danger. Personally I think I did not really comply with the above when I fitted 2 RCD's for the whole of the house, and when I moved I fitted 14 instead. But it is not cut and dried, you have to decide as the designer if what your going to do is reasonable, personally I would say it's not reasonable, but that's a personal opinion.

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There is 'risk' associated with all lights failing. This may or may not constitute a "danger"

Jackrae said:

There is 'risk' associated with all lights failing. This may or may not constitute a "danger"

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Indeed - and, in any event, as I noted above, what the regulation actually says is


Whereas many/most people seem to read it as if it said ...


... in other words, the potential danger (which "may" arise - so, as you say, a 'risk) exists whenever there is a single lighting circuit (in the whole of the house, or maybe even just on one floor thereof), even if it has it's own RCD/RCBO, whereas those who (in my opinion) mis-read the regulation seem to take it to be suggesting that it relates to the risk of a fault on some other circuit 'taking out' the lighting one (because of a shared RCD). Those people may, of course, be right in terms of what was the 'intention' of the reg but, as written, it does not seem to say what they seem to think.

... and, in any event, as has been so often discussed, no number of RCDs/RCBOs can prevent that risk (hence potential danger) arising in the event of a power cut - only emergency lighting can achieve that.

Kind Regards, John

My house has a simple Lidi plug in emergency light at the top of the stairs. And of course anyone for under £20 can fit an emergency light, so can't really say the electrician needs to do anything, it is up to the occupier as to what they do.

As to potential danger, to my mind the largest potential danger is a circuit tripping in the night or snow and my trying to go outside and down a flight of steps into the flat under the house to reset it. And I will simply leave them tripped until morning with anything other than heating of freezers.

So in real terms the biggest risk is not lighting, but socket supplies to my kitchens, upper one I lose freezers and lower one I lose heating, I know where my torches are and can manage without lights until morning, but not without heating or freezers. Yes I should say few hundred for loss of food is not worth the risk, but one always thinks one can do it without falling over.

If I did not need to go outside to reset then it would be different, and garage at last house was same level as entrance floor not under the house like this one, why builders put the DNO heads in a garage I don't know, but it does seem common to have a distribution unit in an integral garage.

Last house at least I had a gas fire, easy to light, so could do without central heating, this house has an open fire, but never lit a fire in the grate.

So yes "... take account of danger that may arise from the failure of a single circuit such as a lighting circuit" does not limit its self to lighting two most important circuits in this house are the kitchen supplies.

ericmark said:

My house has a simple Lidi plug in emergency light at the top of the stairs. And of course anyone for under £20 can fit an emergency light, so can't really say the electrician needs to do anything, it is up to the occupier as to what they do.

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Yes, but recalling all the recent discussions, don't forget that we are talking about satisfaction of a regulation (conformity/compliance with which is 'assessed during an EICR) which some seem to interpret as meaning that an installation must have at least two RCDs, if not all RCBOs - and who, it seems, are not beyond giving a C2 to such things (potentially resulting in very appreciable cost to landlords).

Even if they regarded a "Lidl plug-in emergency light", which had been plugged in by the occupier, to be 'part of the installation' which was within the scope of an EICR, I'm not at all sure that they would regard it as an acceptable way of satisfying (their interpretation of) the regulation, are you?

Kind Regards, John

My interpretation of installation is fixed wiring, not including any appliance, irrespective of the appliance weight or provision of wheels, i.e. it does not need to be hand held or portable, if it is an appliance then not part of an EICR. I regarded the bulb as an appliance not the bulb holder, the thermostat and cable to the immersion heater but not the heater its self, the FCU supplying a boiler but not the boiler its self. And I am only interested in electrical safety, so if I went to a building with only lights and sockets, as with a small industrial unit rented by the council, I am not interested in anything not there, or clearly decommissioned. I am not interested in the fact there are no emergency exit signs, the safety officer may note them, but they are nothing to do with my electrical inspection. It does not matter if an industrial unit or a house, I am not checking to see if every area is lit, possibly some buildings will have no lighting, the old electrics is sockets to plug a vacuum cleaner into.

Now some times I have come to an arrangement, some semi-skilled guy has got the job of PAT testing, and he is going around with a PAT testing machine, and anything which will not plug into the machine I test, but the results are recorded on form V2 - Equipment formal visual and combined inspection and test record, they are not recorded on the EICR forms.

There is nothing on the IET sample form about checking if any light is present or smoke alarm, or many of the items which we see people fail properties on, be it PAT testing or EICR we follow the IET forms in the main as out own check sheet to ensure nothing missed. There are even regulation reference numbers to make checking easier where not sure.

Clearly the IET and the UK Government definition of installation is not the same, but we are working to IET rule book, the government has not yet produced one, so with the IET book we do inspect and report on the DNO head, but not the government one, and we do not look inside the boiler, but do with government one. But there is an option to exclude parts, and we could simply write LIM in the boxes for the Distributors Supply intake equipment.

But to my mind if not listed in the sample forms, we don't test it.