lighting earth question

[mark7600]

Hi
I added some lighting and skts to a new porch. Changed the 2g sw in house next to front door to a 4g to include the new porch and outside light. In the sw I had 7 cables, old 3 core 2w with upstairs landing and 1 way sw for downstairs hall ceiling rose, This is where I got feed from for new lights. So the new lights both are two way with 2g sw in porch.
My question is regarding the earth in the new 4g sw. Should I have connected the earth from the upstairs fed 3 core with the downstairs circuit earths? It was originally so I just joined all earths together. Does it matter? As I have now realised that the two seperate circuits earths are connected. Should I have just made sure i had continuity for upstairs and just put that single earth in connector block? Bit confused.

 

[Deleted member 9648]

As long as lives and neutrals of different circuits are kept separate the earths can all be joined together if in the same box.

 

[mark7600]

thanks , thats great. where do you terminate them? i put them into a connector block with fly lead to back box and metal switch. there were 9 earths!

 

[Sintra]

thanks , thats great. where do you terminate them? i put them into a connector block with fly lead to back box and metal switch. there were 9 earths!

That's fine mate.

 

[patricklondon]

yep fine, in bigger installs lighting circuits from different phases are still put together in grid switches with earths sharing terminals. you were already right but its better to know

 

[pushrod]

If it's ok in this case to link the earths between two different lighting circuits (i think that what the OP is saying) why is it not ok to borrow an earth from a ring to a lighting circuit.

Is it because in this case you are just paralleling an earth and with connecting a lighting circuit (without a cpc) to a ring it is the only path?

 

[mark7600]

Pushrod, I think it is more to do with the size of cpc in 2.5 compared to 1.5 cable, so the calculations for min cable size and dis connection times would be different from the regs requirements?
I have found while carrying out a periodic with my boss a ring connected to the lighting behind a fan, with the earths being shared and using the perm live from the ring for the timer! Naughty.
After we disconnected it, there was no earth in the kitchen. So cost the owner a bit to repair.

 

[pushrod]

Pushrod, I think it is more to do with the size of cpc in 2.5 compared to 1.5 cable, so the calculations for min cable size and dis connection times would be different from the regs requirements?
I have found while carrying out a periodic with my boss a ring connected to the lighting behind a fan, with the earths being shared and using the perm live from the ring for the timer! Naughty.
After we disconnected it, there was no earth in the kitchen. So cost the owner a bit to repair.

cheers Mark hadn't thought about that, but i would be surprised if that made much difference. The size of the cpc in 2.5 T&E is 1.5, It can't be a huge amount different in 1.5 T&E. Plus increasing the size would lower the resistance and so you would get a bigger PFC and a quicker disconnection time?

I thought it was to do with introducing a fault into a separate circuit.

 

[mark7600]

Yes true good point. It would need a fair bit of testing to work it all out as well.

 

[Risteard]

cheers Mark hadn't thought about that, but i would be surprised if that made much difference. The size of the cpc in 2.5 T&E is 1.5, It can't be a huge amount different in 1.5 T&E. Plus increasing the size would lower the resistance and so you would get a bigger PFC and a quicker disconnection time?

I thought it was to do with introducing a fault into a separate circuit.

1.5mm2 T&E has a 1mm2 cpc.

I suspect the reason is to prevent someone inadvertently disconnecting the cpc from another circuit when carrying out work on a different circuit. As such, each circuit must have its own cpc.

 

[pushrod]

1.5mm2 T&E has a 1mm2 cpc.

I suspect the reason is to prevent someone inadvertently disconnecting the cpc from another circuit when carrying out work on a different circuit. As such, each circuit must have its own cpc.

but is it important to keep them completely separate? Some of the earlier posters say it is fine to join CPCs from different circuits

what would linked earths do to the fault finding process (too late in the evening for me to give that serious thought )

 

[sheppy]

Good advice here , Thanks !

 

[gizmo]

Pushrod, I think it is more to do with the size of cpc in 2.5 compared to 1.5 cable, so the calculations for min cable size and dis connection times would be different from the regs requirements?
I have found while carrying out a periodic with my boss a ring connected to the lighting behind a fan, with the earths being shared and using the perm live from the ring for the timer! Naughty.
After we disconnected it, there was no earth in the kitchen. So cost the owner a bit to repair.

More to do with the sharing of the earth ! IE, future works on the ring, say for example installing a new one completely, then the circuit 'borrowing' the earth would no longer have one !