4 submains with one common CPC

[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.

 

[shanky887614]

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.

true there is nothing electrically wrong with it if the cable is large enough but personally i would rather have a seperate earth with each supply.

 

[davesparks]

It is effectively the main earthing conductor to each DB.

An installation can only have one earthing conductor, it is defined as being the conductor which connects the MET to the means of earthing.
The term 'main earthing conductor' does not exist in bs7671

 

[atm84]

true there is nothing electrically wrong with it if the cable is large enough but personally i would rather have a seperate earth with each supply.

I agree but then one doesn't want to create unnecessary work if it's not required.

 

[Deleted member 26818]

To be precise, BS7671 does allow for an installation to have more than one Earthing Conductor.

 

[atm84]

An installation can only have one earthing conductor, it is defined as being the conductor which connects the MET to the means of earthing.
The term 'main earthing conductor' does not exist in bs7671

Dave please refrain from trying to be smart and always trying to catch people out. I apologise for mister meaner. I'm sure you understood what I meant.

 

[Richard Burns]

true there is nothing electrically wrong with it if the cable is large enough but personally i would rather have a separate earth with each supply.

Not a problem for you to do that if you are installing it, I would think it would increase the quality of the installation in many cases and exceeding the minimum standards is generally a good thing, but it is important to be aware that it is permitted to have a single (suitably rated) cable.

 

[shanky887614]

I agree but then one doesn't want to create unnecessary work if it's not required.

? it would take more work to join the cable and link it than to pull it in with the tails.

same route afterall and bs7671 is a minimum standard afterall

 

[atm84]

? it would take more work to join the cable and link it than to pull it in with the tails.

same route afterall and bs7671 is a minimum standard afterall

Its an existing installation. How I would have done it in the first place is kind of irrelevant. I'm just query its suitability as a basis to make additions to the DBs.

 

[Risteard]

The term 'main earthing conductor' does not exist in bs7671

Indeed. I often wonder where the supplementary Earthing Conductors are if one is the main one!

 

[atm84]

Just looking in the regs to find where it says each circuit must have its own CPC and I've come across 543.1.2 in the green book (installation complete in 2011) and it clearly suggests that it is acceptable to have a common protective conductor.