Advice on regulation 521.5.1

S

spadge47

Hi all,

A couple of guys at work are getting return visits to properties because they have been taking the earthing conductor into the new AMD3 metal boards through a separate hole than the tails. Apparently it is against these regs. Now I have read it and I am seeing it from both sides but I need your help.

We have been using the wylex boards with the wylex tail glands, and they have the 2 holes in it ( for line and neutral), however when explaining that if you have to take the earth through the same hole then surely these glands would have 3 holes ? The reply was to 'drill a 3rd hole then'. :thinking:

So please could I have some clarification on this. Do you have to bring the earthing conductor through the same hole as the line and neutral tails for metal boards??

Please could you give me your answers and reasoning please :)
 
only the L and N need to be through the same hole to avoid the possibility of eddy currents in the steel casing.
 
they are quoting 521.5.1 on the technical reports. what could they possibly be misinterpreting to take the earth through?
 
Who are the 'they' who are quoting this?
Whoever they are they obviously don't understand some pretty basic concepts in the science of electricity.
 
they = the electrical quality control managers of the company i work for.

I had never heard of having to bring all cables through the same hole until colleagues had technical reports back.

It seems they are taking the first paragraph of the reg 521.5.1,

'the conductors of an a.c circuit installed in a ferromagnetic enclosure shall be arranged so that all line conductors and the neutral conductor,if any, and the appropriate protective conductor are contained within the same enclosure'.

as 'enter the enclosure through the same entry'.
 
Last edited by a moderator:
spadge47 said:
they = the electrical quality control managers of the company i work for.

I had never heard of having to bring all cables through the same hole until colleagues had technical reports back.
Click to expand...

They clearly haven't got a clue, what would they say if you just bolted the earthing conductor to the side of the cu with a lug?

What do you mean you've never heard of bringing all conductors through the same hole? Are you a trainee?
 
spadge47 said:
they = the electrical quality control managers of the company i work for.

I had never heard of having to bring all cables through the same hole until colleagues had technical reports back.

It seems they are taking the first paragraph of the reg 521.5.1,

'the conductors of an a.c circuit installed in a ferromagnetic enclosure shall be arranged so that all line conductors and the neutral conductor,if any, and the appropriate protective conductor are contained within the same enclosure'.

as 'enter the enclosure through the same entry'.
Click to expand...

Right.
 
sorry - what I mean is that I had never heard of having to bring the earthing conductor through the same hole until the management threw that one out there. ( I know the L-N need to.)
 
spadge47 said:
they = the electrical quality control managers of the company i work for.

I had never heard of having to bring all cables through the same hole until colleagues had technical reports back.
Click to expand...

I expect this is something that is going to become far more talked about over the next year when we have to start fitting metal consumer units (I suppose I should say non-combustible, but it's looking like the manufacturers of the boards are going with steel to comply).

Could you explain why you are 'seeing it from both sides' Spadge? The regulation makes it very clear that all conductors (including CPC) should be brought through the same hole. Some manufacturers are making grommets that specifically take x2 25mm tails and 16mm earthing conductor which look quite good to use.

Have to admit Eddy currents are not something that I fully understand and it would be good to know more. Is this a likely occurance on a single phase domestic supply?
 
Did they not introduce a new Regulation in the 17th allowing a separate earth to be run along side an SWA cable?
Obviously the earth would have to enter the enclosure separately to the other conductors.
 
I can see it from both sides because on one hand as well i could bolt directly onto the side of the consumer unit, therefore no earthing conductor going through the hole., which is the same outcome as going through a separate hole as it doesn't affect eddys currents.)

And I can see it as it says the appropriate protective conductor.

Now if it was a circuit fed from the board i could understand bringing it through the same hole, however as it is tails directly from the meter and an earth directly from the cut-out, why would you need to bring it through the same hole.
 
Last edited by a moderator:
Read and understand the regulation number quoted in the OP and all will become clear.

If the additional cpc is bolted to the outside of the enclosure it is NOT entering the enclosure.
If it is entering the enclosure then it must comply with the reg, thus enter collectively surrounded by ferrous material.
This is not an option it's a reg, end of.
If you don't want to do it, put it as a deviation, else comply simple.
 
spinlondon said:
Did they not introduce a new Regulation in the 17th allowing a separate earth to be run along side an SWA cable?
Obviously the earth would have to enter the enclosure separately to the other conductors.
Click to expand...
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 they 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?
 
Can someone please explain why the Regulations allow a separate earth with SWA to enter ferrous magnetic enclosures, but not when the conductors are not part of an SWA cable?
 
netblindpaul said:
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 they 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?
Click to expand...

The only reason I know of to run a seperate earth is when if is required to meet bonding requirements rather than as a cpc
 
what deems it an appropriate protective conductor?
 
Last edited by a moderator:
spinlondon said:
Can someone please explain why the Regulations allow a separate earth with SWA to enter ferrous magnetic enclosures, but not when the conductors are not part of an SWA cable?
Click to expand...

Probably because the people who wrote the regs realised they had created an impossible scenario and Bodged it up to cover themselves. Pretty much standard 7671 nonsense
 
davesparks said:
The only reason I know of to run a seperate earth is when if is required to meet bonding requirements rather than as a cpc
Click to expand...
dave,
I never mentioned bonding conductor, only referencing a cpc as an "earth" using the term "earth" as it had been used in an earlier post.
A bonding conductor is not part of the circuit that the SWA is supplying.
 
netblindpaul said:
They don't allow it to enter through a different point, never have.
Click to expand...

if you read the final paragraph of 521.5.1 it reads 'the use of an additional protective conductor in parallel with the steel wire armouring of a cable where such is required to comply with the requirements of the appropriate regulations in chapters 41 and 54. it is permitted for such an additional protective conductor to enter the ferrous enclosure individually.
 
netblindpaul said:
dave,
I never mentioned bonding conductor, only referencing a cpc as an "earth" using the term "earth" as it had been used in an earlier post.
A bonding conductor is not part of the circuit that the SWA is supplying.
Click to expand...

How exactly does one inform that bonding conductor that it is not to be a cpc? Regardless of what it gets called it will still be a part of the earth loop and carry it's share of the fault current.
 
Yes, as I said, read and UNDERSTAND the reg.
Where it is REQUIRED.
If it is not REQUIRED then it is NOT ALLOWED.
So, if you can generate a scenario where it is REQUIRED, then it is ALLOWED.
However, I doubt you can actually prove a reason to install a separate cpc.
Look it up do the calcs, and then come back and show where a seperate cpc is REQUIRED, considering that the SWA must act as an adequate CPC for the circuit anyway else it is not acceptable.
 
davesparks said:
How exactly does one inform that bonding conductor that it is not to be a cpc? Regardless of what it gets called it will still be a part of the earth loop and carry it's share of the fault current.
Click to expand...

It's a bonding conductor, NOT a circuit CPC.
They are different items, they, can be combined, however a cpc is a cpc, and it must act as a cpc.
If you want it to be a bond as well then that is something different.

Remember BS7671 only considers a single fault.
 
i'll reword the question.

does a main earthing conductor have to go through the same holes as the main tails in a metal wylex board?

the tails come straight out the meter into a metal board through a wylex gland..

and if so then why does the tt wylex gland only have 2 holes and not 3.
 
spadge47 said:
i'll reword the question.

does a main earthing conductor have to go through the same holes as the main tails in a metal wylex board?
Click to expand...

Yes.
Though what Wylex has to do with it I don't know.
Also remember there is no requirement to fit metal boards until 01/01/16.
Until them flammable and dangerous boards are quite acceptable regardless of what is said on the internet.
 
All conductors of a circuit should enter a ferrous metallic enclosure through the same hole.
I don't know why there has been a relaxation of this requirement in recent years, it may be because it has become industry standard?
 
Unfortunately, my employers have decided to do away with plastic boards last month, can only fit metal.
 
netblindpaul said:
It's a bonding conductor, NOT a circuit CPC.
They are different items, they, can be combined, however a cpc is a cpc, and it must act as a cpc.
If you want it to be a bond as well then that is something different.

Remember BS7671 only considers a single fault.
Click to expand...

How does the conductor know that it is a bond and not a cpc? the armour as cpc and the seperate bond are effectively connected together at each end, so any flow of current is going to split between them proportionally.
 

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Advice on regulation 521.5.1
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