Lighting & ring circuits in same junction box?

[cavas]

Thinking about upgrading my attached garage wiring using 20 mm conduit to run a ring circuit as well as a lighting circuit, both from the house consumer unit. Due to the shape of the garage and the location of the existing wiring, I may have to use one or two junction boxes at various points (32A Adaptable boxes with 5 terminals, which I have spare).

Is it allowable to use the same junction box to carry both lighting and mains circuits using the 5th terminal as earth for both circuits?

Many thanks in advance for any opinions

 

[securespark]

I wouldn't see an issue using the same enclosure, but I would keep the cpcs separate.throughout the circuit

 

[cavas]

Thanks for the response, that will make planning the conduit runs much easier and neater. Yes, they'll be kept separate, the ring is on 2.5 mm T&E while the lighting is on 1.5mm T&E so it should be obvious which terminals in the enclosure are being used for which circuit. I think to be safe I'll also label inside the enclosure which terminals are being used for which circuit so in the future there's no confusion.

 

[securespark]

Just had a thought. Can you upload a diagram showing the proposed layout?

It may be better to try and terminate the ring final cables in the sockets and the lighting cables at ceiling roses or light fittings. This will reduce the number of joints in the circuit.
What is the loading you propose to put on the circuits in the garage?

 

[cavas]

Just had a thought. Can you upload a diagram showing the proposed layout?

It may be better to try and terminate the ring final cables in the sockets and the lighting cables at ceiling roses or light fittings. This will reduce the number of joints in the circuit.
What is the loading you propose to put on the circuits in the garage?

Thanks, yes I'll do that later today, your opinion would be much appreciated. The ring in the garage is already in place, I just need it extended it to the further reaches of the garage for more conveniently placed sockets. DIY power tool loading, possibly a tablesaw at some stage in the future but not much else. Its on a 32A circuit breaker in the house consumer unit.

 

[securespark]

A diagram and pictures is always helpful.
If you want to run 6 ring final conductors and lighting in the same conduit, you may need 25mm.

 

[Taylortwocities]

I would advise that you keep them separate. While it makes no difference if you stuff all the earths together, you may run into major problems if you common up the neutrals.

It depends on how your circuits are wired, but RCDs really object to this sort of thing.

There's also the issue of isolation if someone is working on the circuits. Remember that it may not be you that is doing the work and everybody carries out safe isolation procedures (not).
Handyman comes to do some work on the garage lights, pops off the lighting MCBs, opens up the JB and pops his fingers in - expecting it to be isolated......

 

[cavas]

I would advise that you keep them separate. While it makes no difference if you stuff all the earths together, you may run into major problems if you common up the neutrals. It depends on how your circuits are wired, but RCDs really object to this sort of thing.

Thanks, I know what you mean about neutrals and RCD's, but I wasn't planning on commoning up the neutrals. Just the earths. The JB's have 5 terminals, so i was planning on two for live and neutral for the ring, 2 for live and neutral for lighting, and earths commoned on the fifth terminal.

There's also the issue of isolation if someone is working on the circuits. Remember that it may not be you that is doing the work and everybody carries out safe isolation procedures (not). Handyman comes to do some work on the garage lights, pops off the lighting MCBs, opens up the JB and pops his fingers in - expecting it to be isolated......

Nice example . The JB's have plenty of room in them for labelling with an indelible marker, so I thought I'd mark each termial prominently, not just for the handyman, but for me in the future also! But food for thought, I'll keep thinking.

Was planning on posting a diagram tonight to explain my logic better, but it'll have to be tomorrow now.

Thanks to all who've responded so far, it helps the thinking process.

 

[DetlefSchmitz]

Junction boxes are the work of the devil. There is usually a way to avoid them without too much extra wiring. See what is possible before you commit yourself.

 

[scousespark]

Are you adding new circuits, or taking a feed from those already in place?