Extending supply from garage to another outbuilding

[dram773]

Would appreciate advice please.
Our detached garage has power and lighting circuits supplied from the consumer unit in the house. The sockets are connected to a B32 on a 63A 30mA RCCB. The lights are connected to a B20 on another 63A 30mA RCCB.
The garage lighting circuit has been extended overhead (catenary wire) to provide lighting in a wooden outbuilding about 18m away - switched and fused inside the garage.
We would now like to install a couple of sockets in this outbuilding. Can a fused and switched supply similarly be extended from the garage circuit by attaching another cable to the same catenary wire?
Many thanks

 

[winston1]

For a start get your existing garage lights sorted out. No way should they be on a 20A MCB. 6A is usual, 10A occasionally.

What you are proposing is possible. However I would only have one cable to the outbuilding feeding sockets and the lights taken from this via a FCU with 5A fuse.

 

[dram773]

Hi winston1, many thanks for your response.
My bad - I've checked the consumer unit and that 20A is labelled "garage sockets and outbuilding lights". The 32A is labelled "garage and laundry ring". There is also an additional 6A labelled "laundry lights". The electrics were checked and certificated when we bought the house in July.
So, would it be reasonable for me to ask sparkie to extend the existing garage socket/lights (20A) circuit to provide a couple of sockets in the outbuilding, together with a garage consumer unit?
Cheers!

 

[ericmark]

Lighting circuits incorporating B15. B22. E14. E27 or E40 lampholders shall be protected by an overcurrent protective device of maximum rating 16A.

So seems something wrong, but can't say for sure.

The electrics were checked and certificated when we bought the house in July.

Same two years ago when I bought this house, it said there was a disused fuse box in the ceiling space, actually it was the main fuse box for most of the house.

But if asking an electrician he should check first, so ask the electrician and see what he says.

 

[JohnW2]

Lighting circuits incorporating B15. B22. E14. E27 or E40 lampholders shall be protected by an overcurrent protective device of maximum rating 16A.

So seems something wrong, but can't say for sure.

Perhaps, but if I understand correctly the (20A) circuit in question is labelled (at the CU) as "garage sockets and outbuilding lights" - and, although BS7671 does not go far in defining what constitutes a "lighting circuit" (I think that it said nothing in BS7671:2008, but a footnote to Table 52:3 now says "NOTE 4: For lighting circuits and associated small items of current-using equipment, such as a bathroom extractor fan."), I doubt it is meant to include one which supplies 'garage sockets' (as well an anything else. So maybe it's 'OK' as far as the regs are concerned!

Kind Regards, John

 

[ericmark]

This is why I said can't say for sure. Common to have a switched FCU as light switch which makes it OK.

 

[winston1]

So, would it be reasonable for me to ask sparkie to extend the existing garage socket/lights (20A) circuit to provide a couple of sockets in the outbuilding, together with a garage consumer unit?
Cheers!

Yes. You don't need a garage consumer unit, it is already protected by the 20amp MCB. You will need a switched FCU for the lights however.

 

[JohnW2]

This is why I said can't say for sure. Common to have a switched FCU as light switch which makes it OK.

Fair enough, but I think I am much closer to being "sure" than you appear to be.

Even in the days of your BS7671:2008 (which, to the best of my knowledge, said absolutely nothing about what constituted a 'lighting circuit') common sense suggested that a 20A radial supplying sockets which 'happened' to also be supplying some lights (as you say, probably via an FCU) did not qualify as a 'lighting circuit'.

However, the note added in BS7671:2018, clarifying that supplying "small items ... such as a bathroom extractor fine" did not stop a circuit being a 'lighting' one would seem to very much strengthen that common-sense view.

Kind Regards, John

 

[EFLImpudence]

There seems to be very little common sense in stating that a 'lighting circuit' may supply other items and a circuit that is not a 'lighting circuit' may supply lights.

Much like the only thing that designates a 'cooker circuit' as such must be that it supplies a 'cooker'. Were this circuit, on purchase of a gas cooker, to be used for something else is it still a 'cooker' circuit?
Is a 4mm²/32A radial supplying sockets actually a cooker circuit?


Why is there any need to apply specific conditions, such as a maximum OPD rating or which items may be connected, on so-called 'lighting circuits' when, in fact. they are no different than any other circuit?

 

[JohnW2]

There seems to be very little common sense in stating that a 'lighting circuit' may supply other items and a circuit that is not a 'lighting circuit' may supply lights.

I agree.

Much like the only thing that designates a 'cooker circuit' as such must be that it supplies a 'cooker'. Were this circuit, on purchase of a gas cooker, to be used for something else is it still a 'cooker' circuit?

Quite so.

Is a 4mm²/32A radial supplying sockets actually a cooker circuit?

Functionally, it could be anything you wanted it to be. If you so wished, it could be a "Laundry Appliances circuit", a "Power Tools circuit", an "IT equipment circuit" or anything else that took your fancy!

Why is there any need to apply specific conditions, such as a maximum OPD rating or which items may be connected, on so-called 'lighting circuits' when, in fact. they are no different than any other circuit?

Unless I'm missing something, no 'need' (and, indeed, no apparent sense). In the case of minimum cable CSA, is this perhaps a leftover from the days of BS3036 fuses when (I haven't done the sums) 1.0mm² cable may not have been adequate for (13A or 15A) 'sockets circuits''?

It's good to seemingly be in total agreement about something for once

Kind Regards, John

 

[ericmark]

Why is there any need to apply specific conditions, such as a maximum OPD rating or which items may be connected, on so-called 'lighting circuits' when, in fact. they are no different than any other circuit?

I would say two things, one many ceiling roses are rated 6 amp which limits the amps of a lighting circuit, and the volt drop is limited to 3% which is clearly from the days of using wire wound ballast for fluorescent lights. (Or other discharge lamps).

BS 7671 does refer to "take account of danger that may arise from the failure of a single circuit such as a lighting circuit" as one reason for splitting the supply into circuits, however the way RCD's have been fitted seems to mean little attention has been paid to that? I can't see how two RCD's could have ever complied, but seems I am wrong?

 

[EFLImpudence]

I would say two things, one many ceiling roses are rated 6 amp

Therefore allowing a 16A OPD again makes no sense.

That would make no difference for loop at switch wiring.
If you then say the switch might also be 6A. the same applies.

Of course 13A sockets on 32A circuits is fine.

 

[ericmark]

Therefore allowing a 16A OPD again makes no sense.

That would make no difference for loop at switch wiring.
If you then say the switch might also be 6A. the same applies.

Of course 13A sockets on 32A circuits is fine.

Yes it seems strange that 16 amp is in the regulations, I bought some cheap think 6 watt CFL from Ikea many years ago with the idea it was enough to light side of house, and no need to worry about any PIR, which was correct, but when the bulb failed it went short circuit, and although bulbs should have a built in fuse, clearly these did not, as it welded its self to the bulb holder, which was made worse due to using a 16 amp MCB to feed it. Since most BA22d lamp holders other than porcelain are normally rated at 2 amp, like the 13 amp socket, since a fuse in the bulb or plug having a supply over 2 amp should not matter, but had that outside lamp been on a 5 or 6 amp MCB then likely it would have not welded its self onto the lamp holder.

It does however raise the question as we move from tungsten what other changes are we looking at? I would have never dreamed of swapping a tungsten bulb with the power on, as likely I would burn my hand, so even if the glass broke, I would not get a shock, OK some times used a glove with power on, but same applies, would not get a shock, but with cool lamps likely they will get swapped with bare hands, and also since made of plastic can melt, fire may not have been able to pass a glass GU10 bulb, but plastic? We stopped using polystyrene ceiling tiles as in a fire they could drip hot burning plastic, what about plastic lights?

 

[JohnW2]

... but when the bulb failed it went short circuit, and although bulbs should have a built in fuse, clearly these did not, as it welded its self to the bulb holder, which was made worse due to using a 16 amp MCB to feed it.

You've told that story many times before but, in the face of a 'short circuit', a 16A MCB will operate essentially as quickly (in a small number of milliseconds) as would a 6A MCB (or even 1A one if it existed) - and, as you know, no MCB, of any rating, will limit the magnitude of current which flows before the device operates.

Hence, whilst I obviously believe your story, I find it very hard to believe that the outcome would have been any different had the MCB been 6A, or even lower.

Kind Regards, John

 

[ericmark]

You've told that story many times before but, in the face of a 'short circuit', a 16A MCB will operate essentially as quickly (in a small number of milliseconds) as would a 6A MCB (or even 1A one if it existed) - and, as you know, no MCB, of any rating, will limit the magnitude of current which flows before the device operates.

Hence, whilst I obviously believe your story, I find it very hard to believe that the outcome would have been any different had the MCB been 6A, or even lower.

Kind Regards, John

Yes which is why we don't use MCB's to protect semi-conductors we use semi-conductors fuses as faster than a MCB.