Earthing galv conduit containing multiple circuits

[Tuttle]

I am about to wire my own integral garage. I use it as a workshop so I am thinking about running singles in galv conduit. I've not used singles before and I've only ever used galv conduit to protect T&E run outside of safe zones.

I haven't been able to find any good information on singles / conduit – either books or internet resources (I would be interested if anyone can point me at any) – so I have some rather basic questions I'm afraid. Really, it's earthing that I am unsure of …

I'm planning on running the T&E from the ring main and lighting circuit from an adjacent room through the wall into a conduit box in the garage and then using wagos to go from T&E to singles. I'm planning on running the ring main and lighting circuit in the same galv conduit, each with it's own cpc … I assume that this is correct?

So far it seems the same as T&E except I've got conduit instead of sheaths (ok, I know that switch drops are normally wired a little differently). The problem comes when I earth the conduit … how should this be done? I assume I should use a flying lead from each socket / switch plate to the metal box, but this will connect the cpc of the lighting circuit and the cpc of the ring main together … is that correct / ok?

How does that effect testing? Should I check cpc continuity before connecting the flying leads to boxes / conduit?

I suppose I could just use PVC conduit instead, but I would rather learn how to do it properly

 

[somersetsparks]

Conduit can be used as a cpc, but in your instance I would probably continue the cpc's as it forms part of a T+E circuit. It doesn't matter that the earths of each cct. are joined together, just write down the readings you get, think of the conduit as extra cable. You can do an r2 test on all points of the conduit instaed of doing r1+r2

 

[Lighthouse Phil]

You will also find that the conduit boxes have a 4mm earth lug connection in them. You can use this to earth your conduit.

 

[alarm man]

or just use an earth coupler

 

[Tuttle]

Conduit can be used as a cpc, but in your instance I would probably continue the cpc's as it forms part of a T+E circuit. It doesn't matter that the earths of each cct. are joined together, just write down the readings you get, think of the conduit as extra cable. You can do an r2 test on all points of the conduit instaed of doing r1+r2

Thanks.

What's the advantage of measuring R2 instead of R1+R2 for points on the conduit?

Should R2 be measured with the parallel earth paths in place?

 

[Tuttle]

You will also find that the conduit boxes have a 4mm earth lug connection in them. You can use this to earth your conduit.

Thanks.

Are you suggesting that the conduit only needs to be earthed at one point, i.e. the lug in the conduit box?

Does it need to be connected to the cpc's of all the circuits that it contains or only to one of the circuits?

 

[telectrix]

if you are using cpc's then the conduit itself will be earthed as long a it's all metal. you only need to fly lead the metal box where you are changing from T/E to singles. wire the N direct to the lights, and the L's through the switches.

 

[Tuttle]

if you are using cpc's then the conduit itself will be earthed as long a it's all metal. you only need to fly lead the metal box where you are changing from T/E to singles. wire the N direct to the lights, and the L's through the switches.

Thanks.

Makes sense. One question though ... should I connect he cpc of both circuits to the conduit box or just one of the circuits, say the ring main?

 

[Tuttle]

Now I think about it, there are other situations where the cpc's of various circuits get connected together anyway ... like the "illustration of earthing and bonding conductors" in approved doc P which shows cpcs from a towel rail circuit, shower and lighting circuit all connected together via supplemental bonding in a bathroom ... so I guess that I shouldn't worry about that at all and connect the cpc of the lighting circuit and the cpc of ring main to the conduit at the point where it goes from T&E to singles.

 

[telectrix]

yes. or you could dispense with cpc cables and use the conduit as cpc. less cable pulling. more air space in the conduit.

 

[StuSpiers]

Just make sure your bushes are good n tight.

 

[telectrix]

you can't beat a nice tight bush.

 

[wade88]

much like this

 

[StuSpiers]

View attachment 13336 much like this

Bored?

lol

 

[wade88]

Pfft no.......this is what i do. I am a college lecturer.

 

[telectrix]

just TT the tree.