4 submains with one common CPC

[atm84]

I have a query. 4 distribution boards, each fed by 25mm2 double insulated tails (approx 30m away) in a roof void. Only 1 16mm2 earthing conductor for all 4 submains. The earthing conductor is then connected at the first board and looped to the other three boards. Is this acceptable? I thought BS 7671 states that each circuit should have its own CPC.

 

[atm84]

Was just trying to establish if this is actually a cpc or main earthing conductor we're talking about. But as you've said above if it satisfies most onerous condition it doesn't matter. If it's suitably sized etc.

Cheers

When I initially saw it I thought the same in the fact that as long as it's sized to take the most onerous fault current then it's acceptable till I came across the reg that states each circuit should have its own CPC then I became unsure.

 

[davesparks]

Davesparks rather than trying to find fault with my post and being unhelpful why don't you say what your opinion is and put your neck out there instead of hiding behind screen. What is your opinion? What would you do if you keep across the situation. I've said what I think but like I said I'm not confident and am asking for other people's opinion.

I have already told you what I would do. That is that I would do nothing if the cpc is suitable for the most onerous fault condition as this would be compliant.

 

[davesparks]

When I initially saw it I thought the same in the fact that as long as it's sized to take the most onerous fault current then it's acceptable till I came across the reg that states each circuit should have its own CPC then I became unsure.

Until you can quote the number of this regulation then we can't really help you to understand where or how you may have misinterpreted it.

 

[atm84]

Which regulation number is it? I've never heard of it and it directly opposes the regulation which allows this situation.

Such a regulation would render any steel conduit or trunking installation non-compliant

Like I said I will forward tomorrow when I'm back in the office. That's exactly what I thought when I saw it but when conduit/ trunking is used the CPC is effectively always run with the circuit conductor as they are enclosed in the conduit/ trunking.

 

[atm84]

Until you can quote the number of this regulation then we can't really help you to understand where or how you may have misinterpreted it.

I'll forward it tomorrow. Standby

 

[shanky887614]

Which regulation number is it? I've never heard of it and it directly opposes the regulation which allows this situation.

Such a regulation would render any steel conduit or trunking installation non-compliant

in this case though removing db1 would remove the earth to the other db's as well.


correct me if im wrong but dont the regs say that main bonding should be a continuous cable and no breaks allowed?

 

[Deleted member 26818]

No the Regs do not say such.
That is something the BCOs came up with.

 

[atm84]

in this case though removing db1 would remove the earth to the other db's as well.


correct me if im wrong but dont the regs say that main bonding should be a continuous cable and no breaks allowed?

You are correct in saying that by removing DB1 you would remove the earth to the other DBs. The cable is continuos. It's just looped at each DB.

Something just doesn't seem right about it.

 

[shanky887614]

You are correct in saying that by removing DB1 you would remove the earth to the other DBs. The cable is continuos. It's just looped at each DB.

Something just doesn't seem right about it.

so your saying they didnt cut the cable to get it in?

i don't like the sound of that

 

[atm84]

so your saying they didnt cut the cable to get it in?

i don't like the sound of that

All the Dbs are next to each other. The CPC/ Earthing conductor is bolted to the outside of the enclosure with an M6 nut and washer, there is then a flying lead on the inside of the DB which goes to the main earthing terminal of the DB.

 

[shanky887614]

All the Dbs are next to each other. The CPC/ Earthing conductor is bolted to the outside of the enclosure with an M6 nut and washer, there is then a flying lead on the inside of the DB which goes to the main earthing terminal of the DB.

any chance of a picture, im sure im not the only one that was picturing them in different locations

 

[davesparks]

in this case though removing db1 would remove the earth to the other db's as well.


correct me if im wrong but dont the regs say that main bonding should be a continuous cable and no breaks allowed?

There's no denying the first part, but you can't really guard against complete idiots removing DBs without a clue as to what they are doing.

The regs don't have much to say on bonding conductors being unbroken. And there's nothing to say that the cpc under discussion here is also acting as a main bond.

 

[atm84]

There's no denying the first part, but you can't really guard against complete idiots removing DBs without a clue as to what they are doing.

The regs don't have much to say on bonding conductors being unbroken. And there's nothing to say that the cpc under discussion here is also acting as a main bond.

It is effectively the main earthing conductor to each DB.

 

[Richard Burns]

You have probably read a regulation that each individual circuit must have a cpc and interpreted as each individual circuit must have its own cpc.
There is electrically nothing wrong with supplying the distribution boards using the same piece of cable.

 

[atm84]

Thanks Richard. That's a good point. I hope you are correct. I will double check and let you know. I'll forward the specific reg number and then we can see how we all interpret it.