Industrial earthing problems - again deadly

[brookster]

Don't let Markythesparky confuse you ... I don't know why he has put each circuit requires its 'OWN' cpc as this isn't the case If he's under that impression then maybe he can show the REG' where he gets this from, conduit, trunking, steel wire armouring in a sub main supply can all be part of an earth return for multiple circuits.... re-read my previous post ive explained clearly and also reasons why you cant borrow the cpc like you suggested from an adjacent final circuit.

I certainly wouldn't use trunking as my earth return for a 500kva gen! They also don't allow armor (steel bit) to be used as a CPC anymore it has to be separate conductor (client based).

Run everything in the same size it has supplied to it to a big earth bar on the wall. Run the largest size +50% for earthing goodness from this bar to the main earth at the incoming DB - job done.
All your trunking and tray ect will be earthed from the main board or boards anyway.

 

[Darkwood]

I certainly wouldn't use trunking as my earth return for a 500kva gen! They also don't allow armor (steel bit) to be used as a CPC anymore it has to be separate conductor (client based).

With all due respect im replying regarding the OP's situe' and other than yourself there has been no mention of a Generator had this been the case then my advice would differ but as far as what ive put ill stand by my advice as its within the BS 7671

 

[brookster]

With all due respect im replying regarding the OP's situe' and other than yourself there has been no mention of a Generator had this been the case then my advice would differ but as far as what ive put ill stand by my advice as its within the BS 7671

I would still go separate CPC, every job I would run a separate CPC doesn't matter if its a light or a MVA gen.
What happens if one of your return trunking bends falls off the full system is kapoot?
They do get 'shared' though, just not using the mechanical protection of the install.

 

[Darkwood]

Im not nor have I ever said anything against the preferred method of having separate cpc's for each circuit, I was merely commenting on OP's confusion with the regs regarding cpc's been used for multiple circuits and using conduit, trunking etc always has been and is still a perfectly acceptable way to provide an earth and just because you practice other methods through preference doesn't mean its in anyway poor practice to use conduit or trunking as earth, im confused at your comment about the trunking bending or falling off ...you can say that about anything ...what if the earth terminal comes loose, or the earth breaks ....approaching the debate with that kind of thinking won't help the OP it will only lead to more confusion ....as I said im referring to the BS 7671 and if you do have a look it does stress that trucking, conduits etc should be mechanically sound so I cant see anyone having a problem if they decided to use it for earthing... to note though you cant just use anything metal as an earth path it has to meet criteria set in the regs.

 

[brman]

I'm going to stick my neck out a bit here and side (partially) with the op here.

I see darkwoods argument about the danger of borrowing a cpc from another circuit but I am struggling to find an actual regulation that says you can't. Plus I had exactly this problem with a domestic (class 1 lights without a cpc on the cct) where I was doing a CU change. I asked elecsa's helpline and got a clear answer - "yes you can borrow the cpc from another circuit as long as you make a note of it on the cert, after all you are just making it safer".

As long as you are making things safer (and safe to an acceptable level) and have documented what you have done and why then why not if it is all the customer/boss with accept? If you are worried about someone disconnecting the other circuit then stick a nice big label on the DB.

Having said all that, I do worry about doing the work without it being authorised by the management. That does leave you a bit open if the **** starts flying, especially if some pedant can show you have actually made things worse in some way (eg further compromised the IP rating etc).

 

[PEG]

Sympathies with the OP but maybe the company is having to make cuts due to the money they have wasted having inspections carried out only to ignore the findings...

 

[Engineer54]

I read it that each circuit requires a designated CPC.
So each circuit must have a fixed path to earth.
I do not think that each designated earth path must be unique.
As in, if you have a factory earth tape, each circuit has a CPC to the earth tape, then the earth tape becomes the CPC for multiple circuits at once.

Unsurprisingly this CPC would need to be marked at every point that it is used by multiple circuits.

If this is not the case, why is there a reg that says shared CPCs need to be rated only for the largest circuit?

p.s, You would also share a CPC on a sub-main.

I'm not going to get further involved in this argument, i've clearly made my veiws on this matter in earlier posts on this thread.


What i will say here, is that earthing tapes, around a factory wall are not provided as a means of supplying circuit CPC's, they are there as a supplementary means of bonding equipment and isolated extraneous metalwork and the like.

 

[vaughant]

Personally I'd phone HSE if I were the op as this sounds like a timebomb waiting to go off.

that way it MUST be fixed,I'm sure one of the directors can keep his 2 year old BMW M5 another year rather than changing it for new.