Advice on regulation 521.5.1

[davesparks]

Spoken to the NICEIC today. The context of the appropriate protective conductor in regulation 521.5.1 doest include a main earthing conductor as its not part of an a.c circuit in bs7671.

dont shoot me its just what ive been informed!

Forget the NICEIC for a minute and just think about the possibly scientific reasons behind this.
I am only basing this on my own conclusions about this. If a fault occurs which causes a significant current to flow though line and earth, then if they pass through seperate holes this will create its own significant eddy currents in the steel.

 

[spadge47]

But the metal board will be earthed....

 

[shanky887614]

But the metal board will be earthed....

thats what i was getting at earlier.

there is no need to have the earth going in the same hole because it is at the same potential as the case.

unlike L and N which will be at 230+ potential to the case/earth

 

[netblindpaul]

Potential of the enclosure has nothing to do with reducing eddy currents.

 

[spadge47]

Its all starting to make sense... *eyes opened*

 

[spadge47]

No but if the metal board is earthed it is exactly the same as having a cable running through the same hole as the metal surrouning the whole is the earth. Makes no difference.. Sorry for the terrible explanation but at least it makes sense in my head

 

[netblindpaul]

No it's not, the metal enclosure would be at earth potential.
The CPC entering the enclosure would be carrying a fault current, and would be insulated from the enclosure as it passed through.
Thus there would be a potential between the case of the CU & the point at which the CPC passed through the case due to the resistivity of the cable.
Surely this is not that hard to grasp?
Now even though the cable resistivity would be low, hopefully the fault current would be high, which would make the eddy current generation high also, now this would generate a heating effect in the ferrous enclosure.
etc. etc.

Why try to find a way of not complying when complying is easier.

As far as the NIC technical helpline goes...

 

[spadge47]

But we are on about the main tails and earthing conductor... Not a cpc from a circuit.

i could understand if a circuit from the board, but cant with the earthing conductor as i wouldnt class that as the appropriate protective conductor, as the main bonds are also assoiated etc..

 

[Risteard]

But we are on about the main tails and earthing conductor... Not a cpc from a circuit

Irrelevant. It is still the associated protective conductor, with the same effects.

 

[netblindpaul]

Dear Lord,
Forgive me for my sins...

 

[spadge47]

Im going by what the niceic have stated.
Im sure there are plenty of people who believe they know better but as i work for a company registered in their scheme, i ultimately take their interpretation.

Thankyou to all who have posted their arguements, and its good to know that electricians differ completely.


ps. Hilarious comment -_-

 

[ImpededLoop]

.... and its good to know that electricians differ completely.

I don't think it's so much that electricians differ, it's that people have different levels of understanding. This has been an interesting thread to read and it certainly gets you thinking!

As ever, you shouldn't soley trust the advice of a forum and so I'll be getting the theory books out soon to make sure that I'm confident of my understanding.

 

[Paul.M]

OK this thread has been reported due to a heightened state of debate that may turn personal. (Its not that bad btw lol)

I'll put 20 pence in the duke box so we can all listen to a nice bit of calming music, here goes:-

https://www.youtube.com/watch?v=OfJRX-8SXOs

 

[davesparks]

thats what i was getting at earlier.

there is no need to have the earth going in the same hole because it is at the same potential as the case.

unlike L and N which will be at 230+ potential to the case/earth

Potential has got bugger all to do with it. The neutral is at substantially the same potential as the case and that doesn't stop eddy currents occurring.

 

[HappyHippyDad]

OK this thread has been reported due to a heightened state of debate that may turn personal. (Its not that bad btw lol)

I'll put 20 pence in the duke box so we can all listen to a nice bit of calming music, here goes:-

https://www.youtube.com/watch?v=OfJRX-8SXOs

It's actually quite a good thread paul.

Theres a bit of silliness and provoking language but it's not too bad and the main thing is everyone is actually contributing, unlike in the past where there would have been posts solely designed to cause offense.

Let's see if the music has helped :smile5:


ps... Although as for whether the Main CPC should go through the same hole as the tails I'm far more confused than when I first read the reg!! I think I'll stick to what the reg says and have all three together, thus it avoids any problems with those eddies and complies with BS7671.