Advice on regulation 521.5.1

[davesparks]

It's not uncommon with larger sizes Dave, over 50 or 70mm.

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

 

[netblindpaul]

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%

 

[netblindpaul]

View attachment 29571
Where PME conditions apply the earthing conductor must meet the requirements of a main bond.
For the other earthing systems the earthing conductor automatically meets the requirements obviously

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.

 

[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

 

[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!

 

[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.

 

[Paul.M]

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:

Yes it is a good thread but it has been reported and we thought a bit of chill out music was the best option. Next time DW is picking the track

 

[HappyHippyDad]

Yes it is a good thread but it has been reported and we thought a bit of chill out music was the best option. Next time DW is picking the track

You do realise I now have Nina Simone blaring out! The link lasts for 1 hour 15 minutes and 33 seconds!!

 

[andyb]

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.

I agree with all this hhd, I must admit that until this thread I was unaware that the protective conductor of a circuit needs to enter with the live conductors. (I'm talking about a ferrous metal enclosure for any pedant out there)

As an aside, how much current and for how long would need to flow through a conductor for it to be a problem?
It seems to me that if a fault current flows for long enough and does not operate the ocpd then you have a bit more of a problem that a piece of metal getting warm.

 

[Deleted member 26818]

Rather than asking the NICEIC for advice on what the Regulations mean, perhaps you should try asking the IET.

 

[Risteard]

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.

How is there any confusion? The Earthing Conductor is a protective conductor so the Regulation is clear and explicit.

I don't understand the confusion. A number of years ago I flagged up the issue during initial verification where the three phases and the neutral entered a switch fuse through one entry and the Earthing Conductor through another. The NICEIC Approved Contractor I was working for tried to tell me that I was wrong about protective conductors being subjected to the same rules as the live conductors but it is and always has been stated very clearly in the Regulations.

 

[HappyHippyDad]

How is there any confusion? The Earthing Conductor is a protective conductor so the Regulation is clear and explicit.

I don't understand the confusion. A number of years ago I flagged up the issue during initial verification where the three phases and the neutral entered a switch fuse through one entry and the Earthing Conductor through another. The NICEIC Approved Contractor I was working for tried to tell me that I was wrong about protective conductors being subjected to the same rules as the live conductors but it is and always has been stated very clearly in the Regulations.

You're confused about the confusion and I'm confused about your confusion about the confusion!

 

[davesparks]

As an aside, how much current and for how long would need to flow through a conductor for it to be a problem?
It seems to me that if a fault current flows for long enough and does not operate the ocpd then you have a bit more of a problem that a piece of metal getting warm.

Considering that fault currents can be in the thousands of amps it will probably take a fraction of a second for the eddy currents to become a problem. Don't forget current has more effects than just heating the conductor, the magnetic fields will cause mechanical stress at those levels.

 

[Dave OCD]

No, I hate children
Wtf does having kids have to do with it?

Why does this not surprise me ?

 

[davesparks]

Why does this not surprise me ?

Which bit?

 

[Dave OCD]

It just came into my head Dave, bit strong saying you hate kids though, you were one once ? :smiley2:

 

[interlude]

Why spin?
it has always been acceptable, whilst ill advised to run a "separate" earth (cpc) alongside an SWA, as both the SWA & the "earth" must be capable of carrying the full fault current and suitably terminated to meet the requirements, so it is just a waste of money to do this.
So nothing has changed.
It is still stupid to waste money on a separate cpc, so why bother?

This is something we have always adhered to, but what regulation does it actually come from?

 

[Deleted member 26818]

It doesn't come from any Regulation.
There is a requirement where high integrity earthing is required for both CPCs to be selected so that each satisfies the requirements for a CPC.
However there is nothing in standard circuits to prohibit the use of two conductors which will only satisfy the requirements for a CPC when combined.

 

[netblindpaul]

This is something we have always adhered to, but what regulation does it actually come from?

543.1.1

 

[Deleted member 26818]

411.3.2.6

 

[netblindpaul]

Where does supplementary bonding come under the realms of a circuit protective conductor?

 

[davesparks]

It just came into my head Dave, bit strong saying you hate kids though, you were one once ? :smiley2:

Hate as in I have a phobia of them. I cannot stand to be in close proximity to small children and babies.

 

[Darkwood]

Hate as in I have a phobia of them. I cannot stand to be in close proximity to small children and babies.

Your life must have been hell at school then

 

[andyb]

Considering that fault currents can be in the thousands of amps it will probably take a fraction of a second for the eddy currents to become a problem. Don't forget current has more effects than just heating the conductor, the magnetic fields will cause mechanical stress at those levels.

Have to take your word for that Dave, it's a science that I know nothing.
I did a job a couple of weeks back where the lives to a three phase board were all taken into the board through their own neatly drilled 20mm hole. At the time each phase was drawing about 20a, there was no heat or sign of any damage. It had been like this for 20 years.

 

[Midwest]

Thought I would invest in the latest copy of Guidance note 1, Selection & Erection. Curious, I looked up 'Ferromagnetic enclosures, cable entering; (521.5.1) All the conductors of a circuit should generally follow the same route. Live cables of the same circuit may cause overheating if they enter a ferromagnetic enclosure through different openings (page 97, 7.4)

 

[shanky887614]

Thought I would invest in the latest copy of Guidance note 1, Selection & Erection. Curious, I looked up 'Ferromagnetic enclosures, cable entering; (521.5.1) All the conductors of a circuit should generally follow the same route. Live cables of the same circuit may cause overheating if they enter a ferromagnetic enclosure through different openings (page 97, 7.4)

exactly what i was getting at, the earth is only live during fault conditions

 

[Risteard]

exactly what i was getting at, the earth is only live during fault conditions

That isn't true. There will be a certain amount of legitimate earth leakage from appliances. Don't forget that there is functional earthing as well as protective earthing.

And as pointed out, under fault conditions there could be a significant current flowing.

 

[Deleted member 26818]

Also there will be some voltage and current on the earth conductor where PME conditions apply.

 

[R G]

So are the wylex tail glands with the 2 holes only not be used then?

Wiska make glands that have 3 holes in and made for this purpose ..

 

[Dave OCD]

Hate as in I have a phobia of them. I cannot stand to be in close proximity to small children and babies.

That's an unusual one, I have the same problem with snakes.:smile5:

 

[Lucien Nunes]

When the SWA is used as the CPC outside the box, and a length of 6491X lugged onto the banjo bolt serves on the inside, the low resistance path connecting them together is via the brass of the banjo and the bolt, rather than through the enamelled steel enclosure which might make relatively poor contact and is of lower conductivity compared to the brass. So in the event of a fault the banjo bolt carries most of the fault current through a separate hole.

What's the solution? Single hole banjo? Moebius bolt that goes through both holes and back to where it came from? Slot the banjo bolt hole across to the gland entry?

 

[R G]

That's an unusual one, I have the same problem with snakes.:smile5:

Funny that I have the same , must stay off this forum ...

 

[netblindpaul]

When the SWA is used as the CPC outside the box, and a length of 6491X lugged onto the banjo bolt serves on the inside, the low resistance path connecting them together is via the brass of the banjo and the bolt, rather than through the enamelled steel enclosure which might make relatively poor contact and is of lower conductivity compared to the brass. So in the event of a fault the banjo bolt carries most of the fault current through a separate hole.

What's the solution? Single hole banjo? Moebius bolt that goes through both holes and back to where it came from? Slot the banjo bolt hole across to the gland entry?

Do like I do and put the banjo inside?
Not an issue really outside or inside, the contact area is greater inside, than out.
Don't drill the enclosure, why would you?

 

[Dave OCD]

That isn't true. There will be a certain amount of legitimate earth leakage from appliances. Don't forget that there is functional earthing as well as protective earthing.

And as pointed out, under fault conditions there could be a significant current flowing.

There is no functional earthing in a domestic installation.

 

[Risteard]

There is no functional earthing in a domestic installation.

There mightn't be much, but I wouldn't say none (on appliances).

 

[Lucien Nunes]

Indeed, functional earthing is where most legitimate leakage current comes from. Not that it has anything much to do with eddy currents - they start being a problem with hundreds of amps, not a few mA.