Advice on regulation 521.5.1

[Leesparkykent]

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

True but Its personal preference and Imo the wiska gland provides for better Ingress protection. Also the gland supports the tails which an open grommet wouldn't.

 

[netblindpaul]

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

So what does it bond dave?

 

[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.

Which regulation says there must only be one means of earthing?

 

[andyb]

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

They have Dave, openings to IP2X
I use 32mm grommets, once the tails are fitted they comply with that.

 

[davesparks]

So what does it bond dave?

Depends on the earthing system I guess, but if it wasn't a bond then it wouldn't be required to comply with the requirements of a bond would it?

 

[davesparks]

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

Yes it is uncommon, a seperate cpc is almost never required with SWA.
The only time a seperate protective conductor is normally required is to fulfill the requirements of a main bond.

 

[netblindpaul]

Depends on the earthing system I guess, but if it wasn't a bond then it wouldn't be required to comply with the requirements of a bond would it?

It doesn't it must comply with the requirement of an earthing conductor, and depending on the means of earthing this has differing requirements, derived from ESQCR & BS7430.

 

[netblindpaul]

Which regulation says there must only be one means of earthing?

Seriously?

 

[davesparks]

It doesn't it must comply with the requirement of an earthing conductor, and depending on the means of earthing this has differing requirements, derived from ESQCR & BS7430.

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

 

[andyb]

Yes it is uncommon, a seperate cpc is almost never required with SWA.
The only time a seperate protective conductor is normally required is to fulfill the requirements of a main bond.

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

 

[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!