Advice on regulation 521.5.1

[davesparks]

Could do put personally I would use the wiska gland in domestic.

I won't, a 32mm grommet has worked fine for me in CUs since I started my apprenticeship.

 

[andyb]

Read and understand the relevant reg.
IF the 3 conductors are part of the same circuit then they must be collectively surrounded by ferrous material, unless they come under the deviation in the 3rd paragraph.
Someone has posted a pic of the book earlier, look at it, read it and understand it, then all will become clear.

You may call it a deviation, others call it reg 521.5.1 paragraph 3.

 

[Leesparkykent]

I won't, a 32mm grommet has worked fine for me in CUs since I started my apprenticeship.

Happy days! Do you have kids?

 

[davesparks]

No Paul, this is your post No 24



You slipped the 'required' red herring in later, I assume when you actually read 521.5.1

Why do you keep repeating the word 'required' it's irrelevant. You either can or you can't bring the protective conductor through a separate opening.

You can't (unless it is a protective conductor which is running in parallel with the armour of an SWA cable.)

 

[andyb]

You can't (unless it is a protective conductor which is running in parallel with the armour of an SWA cable.)

So you can then.

 

[davesparks]

Happy days! Do you have kids?

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

 

[Leesparkykent]

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

Well I wouldn't want a 32mm grommet on the bottom of a CCU in a cupboard that a kid could easily get in to.

 

[netblindpaul]

No Paul, this is your post No 24



You slipped the 'required' red herring in later, I assume when you actually read 521.5.1

Why do you keep repeating the word 'required' it's irrelevant. You either can or you can't bring the protective conductor through a separate opening.

I keep repeating the word REQUIRED because that is what is REQUIRED by BS7671.

I stand by my post, the regs never have "allowed" a separate cpc to enter an enclosure unless collectively surrounded by ferrous material.
Now if the regs "REQUIRE" this, then that is a different matter.

Look, the interpretation is all down to the language, and the language is subtle but, specific.
One must understand the differences.

You can only bring the additional protective conductor in through a different opening if said conductor is REQUIRED under BS7671 to be installed in parallel with an SWA, so it's NOT a red herring, read the reg FFS.
If you just decide that you are going to run a separate "earthing" conductor in parallel with an swa just because you fancy it, then it MUST enter the enclosure collectively surrounded by ferrous material.
IF you have sat down and done all the design calculations and these show that your SWA is inadequate as a cpc and you must run a separate "earthing" conductor then it is OK to enter through a separate entry into the ferrous enclosure, thus not collectively surrounded by ferrous material.
HOWEVER, if your calculations show that your SWA is inadequate as a cpc, then you must bring your design calculations into question as you must ensure that your circuit complies with BS7671, and if it requires a separate "earthing" conductor then it is doubtful it does.
Look into it, do the calcs and check it out, then look back at the reg and it's associated regulations.

 

[davesparks]

Well I wouldn't want a 32mm grommet on the bottom of a CCU in a cupboard that a kid could easily get in to.

I'm really not following you here? Are you suggesting that we need to take account of bad parents when installing CUs?

(It's hard to resist making pedantic comments about goats here)

 

[Leesparkykent]

I'm really not following you here? Are you suggesting that we need to take account of bad parents when installing CUs?

(It's hard to resist making pedantic comments about goats here)

Haha... I don't see the harm of it being considered in a domestic situation for the sake of £13

 

[netblindpaul]

You need to look at the definitions of earthing conductor, bonding conductor and circuit protective conductor.
On any electrical installation there must only be one means of earthing, thus the earthing conductor connects the installation to the means of earthing.
Now that could be any of the supply systems.
However, said earthing conductor then becomes part of the "sub-main" supplying the distribution board at the origin of the installation.
Now, regardless of where the supply originates from, or the means of earthing goes to, the Line, Neutral and earthing conductor connected between the means of earthing for the installation and the MET of the "first" "DB" in the installation all form part of the same supply circuit, thus they all must collectively enter any ferrous enclosure.
The same applies to any outgoing circuits.
Now bonding conductors are something totally different, they exist simply to create an equipotential zone in the installation.
They are not there by design to carry any fault currents within a supply circuit.
The distinction MUST be understood.
Thus they do NOT form part of any supply circuit, thus they are not part of the requirements of 521.5.1.
Therefore the earthing conductor of an installation is not an equipotential bonding conductor, thus, there are differing requirements for the three kinds of conductor.

Come on this is basic stuff FFS.

 

[davesparks]

Haha... I don't see the harm of it being considered in a domestic situation for the sake of £13

Why now though? For more years than I've been alive electricians have used a grommet or a bush for the job. If there was a problem with children (or goats) then I'm sure the IET would have given us a daft regulation to deal with it, they have after all create this nonsense about non combustible boards

 

[davesparks]

You need to look at the definitions of earthing conductor, bonding conductor and circuit protective conductor.
On any electrical installation there must only be one means of earthing, thus the earthing conductor connects the installation to the means of earthing.
Now that could be any of the supply systems.
However, said earthing conductor then becomes part of the "sub-main" supplying the distribution board at the origin of the installation.
Now, regardless of where the supply originates from, or the means of earthing goes to, the Line, Neutral and earthing conductor connected between the means of earthing for the installation and the MET of the "first" "DB" in the installation all form part of the same supply circuit, thus they all must collectively enter any ferrous enclosure.
The same applies to any outgoing circuits.
Now bonding conductors are something totally different, they exist simply to create an equipotential zone in the installation.
They are not there by design to carry any fault currents within a supply circuit.
The distinction MUST be understood.
Thus they do NOT form part of any supply circuit, thus they are not part of the requirements of 521.5.1.
Therefore the earthing conductor of an installation is not an equipotential bonding conductor, thus, there are differing requirements for the three kinds of conductor.

Come on this is basic stuff FFS.

The earthing conductor performs the functions of both cpc and bonding conductor. It is even sized with consideration to fulfilling both requirements.

 

[andyb]

It's late and I'm off to bed, you're not making sense to me.
Spin stated

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.

You replied

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.

That's quiet clear to me.

It's not uncommon for a separate cpc to be required with swa when you get to larger csa armoured.

 

[Andy78]

I don't know about goats, but there is certainly a lot of bleating going on here

It seems this discussion about eddy currents has induced a rather circular effect. I'm sure the feeling's mutual.