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It is uncommon for it to be required, this is not the same thing as not being uncommon to see one installed. If is very common to see a seperate cpc being installed unnecessarily
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It is uncommon for it to be required, this is not the same thing as not being uncommon to see one installed. If is very common to see a seperate cpc being installed unnecessarily
Now that is something I will agree to 1000%
If you read the actual words it says that it must meet the cross sectional area requirements for a main bonding conductor, not that it acts as one.
The weasel words are there to mean specific things, this is why it seems that there are so many interpretations of the regulations.
The IEC write them in a particular way to mean very specific things, the trouble that we have is that there are some changes when the document becomes an EN, then some more when it becomes a BS.
Also, the meaning of the words is exactly correct for what those who wrote them wanted them to say, however, they are the only ones who know what they wanted to say, the rest of us just have to guess!
Sometimes you need to look at the design intent of the regulation to see why they word it that way, and look back to try and second guess the FMEA's that have been done to come up with that regulation.
G
S
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.
S
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
S
S
S
Irrelevant. It is still the associated protective conductor, with the same effects.
S
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.
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.
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.
Discuss Advice on regulation 521.5.1 in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net
It is uncommon for it to be required, this is not the same thing as not being uncommon to see one installed. If is very common to see a seperate cpc being installed unnecessarily
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Now that is something I will agree to 1000%
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If you read the actual words it says that it must meet the cross sectional area requirements for a main bonding conductor, not that it acts as one.
The weasel words are there to mean specific things, this is why it seems that there are so many interpretations of the regulations.
The IEC write them in a particular way to mean very specific things, the trouble that we have is that there are some changes when the document becomes an EN, then some more when it becomes a BS.
Also, the meaning of the words is exactly correct for what those who wrote them wanted them to say, however, they are the only ones who know what they wanted to say, the rest of us just have to guess!
Sometimes you need to look at the design intent of the regulation to see why they word it that way, and look back to try and second guess the FMEA's that have been done to come up with that regulation.
OP
GEOFF S
I agree with dave, where a system is PME the eathing conductor it needs to meet the requirements for a bonding conductor also, size to the greatest, obvious reason's, broken pen, diverted neutral current will flow down it possibly, as it may the extraneous conductive parts.
Cheers
Cheers
OP
spadge47
Spoken to the NICEIC today. The context of the appropriate protective conductor in regulation 521.5.1 doesnt include a main earthing conductor as its not part of an a.c circuit in bs7671 as it is classed as a separate entity.
dont shoot me its just what ive been informed!
dont shoot me its just what ive been informed!
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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.
OP
spadge47
But the metal board will be earthed....
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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
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Potential of the enclosure has nothing to do with reducing eddy currents.
OP
spadge47
Its all starting to make sense... *eyes opened*
OP
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
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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...
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...
OP
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..
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..
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Irrelevant. It is still the associated protective conductor, with the same effects.
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Dear Lord,
Forgive me for my sins...
Forgive me for my sins...
OP
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 -_-
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 -_-
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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.
- Reaction score
- 5,807
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
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
- Reaction score
- 17,195
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.
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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.
Reply to Advice on regulation 521.5.1 in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net
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