garage electrics: light radial

[Fred]

Hi,

It seems the recommended thing to do is fit a 40A consumer unit in the garage for a 32A ring and 6A lights, or as someone suggested in another thread, have a 16A radial for sockets and a 16A radial for heating. They are all very good suggestions but I'm wondering about the 6A mcb for lighting. Is there any reason that I could not have the lights powered from the house CU?

I realise it would be a good idea to have a separate mcb for outdoor lights and not use the mcb for the house lights. It's just that it seems to me that if I used the mcb in the garage for all my outdoor lights, I would make sense to have them switched from the garage and I don't want to have to walk to the garage in the dark to switch the lights on!

It would make sense to have the switches for the outdoor lights in the house, so why not run them from the house CU? This would leave me with only the lights inside the garage and it seems a bit silly to have an MCB for just two bulbs. Could I connect these to the outdoor light radial or a 3A FCU off the garage spur (32 or 16)?

TIA

[chris French]

In message , Fred writes

Yup, that bit seems sensible.

Someone else will know if the regs have something to say about this. But having garage lights on the external lights circuit from the house doesn't seem like a good idea. sooner or later some one is going to either be lazy or not realise and work on then lighting circuit when not isolated.

Yes, you could do that, but really, it's probably not really going to be much different in cost to run a separate circuit, as opposed to a fused spur so I would do the latter.

[george [dicegeorge]]

Why not have the 2 garage lights on the same circuit as the sockets#? Have a battery backup emergency maintained light for when the garage power trips in the dark. And for when all the electric trips. ? [g]

[John Rumm]

Only that you would need separate wires - one for the submain to the garage, and others for the lighting.

It makes even more sense to not have internal and external circuits sharing a RCD. (the latter are more likely to suffer problems with water ingress and hence electrical leakage - and you don't want to import that problem inside!)

Do you want them on all the time, or would PIR control be more sensible?

That's ok. I would suggest a separate section of CU (or a separate CU) with all the outside circuits grouped together.

If you are going to the bother of having a CU in the garage, and its going to have lights inside, then I would have a circuit on that CU for those lights. No point in not doing so really - and its the logical place for it. If you are not having a CU there, and just a radial fed from the house, then you can just take a fused branch from that for the lights.

As with all these things, think through the failure modes and decide what is acceptable. In my garage I have a split load CU. The RCD protected side feeds the socket ring (about 16 doubles), and the external lights on the garage and workshop, plus a feed to one garden light that is close by. The three lights are switched together by two PIRs. The non RCD side of the garage CU (which is downstream of a 100mA Type S RCD in the outbuilding CU in the house), has the internal workshop and garage lights on their own circuit. That way a power trip caused by doing something silly with a power tool, will not also lose lighting in the workshop.

[Fred]

I'm still wondering about that. PIR when it works is good because it is "automatic" but I have found some makes are a fiddle to set-up. They either stay on for one second after they sense a movement or stay on for half an hour, and it seems to be impossible to adjust them to anywhere between he two extremes!

know you are supposed to be able to override the PIR by switching on, off, and on again but I've never found that to work well in practice either ;(

That makes sense but would you fit this second CU in the house and then run two cables outside (1.5mm^2 for lights and 6mm^2 for sockets) or is the argument that you may as well fit the second CU in the garage?

Yes, I've heard that said before and it sort of makes sense. OTOH I sometimes wonder what would happen if the RCD on the light circuit tripped and the power tool circuit remained on?

Thanks.

[John Rumm]

If you go for stand alone PIRs rather than ones built into lamp fittings, the quality and adjustments available tend to be better.

For garage power and lighting I would run one submain to the garage, and then fit a CU there.

Well, that is also not welcome, although far less likely to happen. I would suggest at least one emergency light in a workshop is a good precaution. They are cheap enough and can mitigate quite a number of potentially dangerous situations.

[chris French]

Yup. The one I used in the old house for the lights outside the back door under the carport didn't use the annoying 'switch on and off technique for turning on permanently. I then wired it in 3 core and earth to give a switched live and well as the PIR controlled live.

But presumably you could use such a system with the othwr sort of PIR

[John Rumm]

Yup, running 3&E for PIR switched lamps is good practice I find. It makes it easy to decide which lamps are controlled by which PIRs and gives the greatest flexibility in future.