Bonding - CU or Main Incoming Fuse

[jshailes]

I'm aware that a 10mm earth cable needs to run to the incoming water and gas supply but I was wondering if someone could tell me whether this should be from the consumer unit, the main incoming fuse, or both? TIA

 

[telectrix]

bonding should be to the MET. this may be the strip in the CU or external. then main earth conductor to head if pme.

 

[Pete999]

I'm aware that a 10mm earth cable needs to run to the incoming water and gas supply but I was wondering if someone could tell me whether this should be from the consumer unit, the main incoming fuse, or both? TIA

There are some videos/articles that suggest that distances between the MET and the point of entry of Gas and Water then the Main bonding conductor should be increased to 16mm2, this is a suggestion from people more in tune with this subject than myself, just passing on some information I have heard and seen.

Like I said if you don't agree, then don't blame the delivery Boy please.

 

[Pete999]

There are some videos/articles that suggest that distances between the MET and the point of entry of Gas and Water then the Main bonding conductor should be increased to 16mm2, this is a suggestion from people more in tune with this subject than myself, just passing on some information I have heard and seen.

For your information and assimilation.

 

[jshailes]

Thanks guys. Looks like mine is TN-S. In case anyone else finds this thread, I found this post useful: Domestic - Earthing Arrangements Explained + Photo's - https://www.electriciansforums.co.uk/threads/earthing-arrangements-explained-photos.59354/

 

[Risteard]

There are some videos/articles that suggest that distances between the MET and the point of entry of Gas and Water then the Main bonding conductor should be increased to 16mm2

They are incorrect. Nowhere does BS7671 state or in any way imply that there is a 0.05 Ohm limit to a main protective bonding conductor. This measurement is intended to prove that the connection between the main protective bonding conductor and the extraneous-conductive-part is effectively made. It has absolutely nothing to do with conductor resistance.

 

[Deleted member 9648]

If the MET is not in the CU or main switchgear then a 'Safety Electrical Earth Do Not Remove' label is required. This is often overlooked

 

[Dave OCD]

Shouldn't it also be labelled as the MET if external to the CU too ?

 

[Risteard]

If the MET is not in the CU or main switchgear then a 'Safety Electrical Earth Do Not Remove' label is required. This is often overlooked

I would overlook it too and instead fit one which reads "Safety Electrical Connection Do Not Remove" ;-)

 

[westward10]

They are incorrect. Nowhere does BS7671 state or in any way imply that there is a 0.05 Ohm limit to a main protective bonding conductor. This measurement is intended to prove that the connection between the main protective bonding conductor and the extraneous-conductive-part is effectively made. It has absolutely nothing to do with conductor resistance.

Funny you should bring this up did the 18th Ed update yesterday and the tutor mentioned this figure and I asked where it was stated in the Regs which drew a blank look.

 

[Deleted member 9648]

I would overlook it too and instead fit one which reads "Safety Electrical Connection Do Not Remove" ;-)

Nitpicker…..

 

[Strima]

There is a calculation in the book based on the size of the largest protective device for bonding, I can't for the life of me remember where it is. I'll have a look for it later.

 

[Deleted member 9648]

Shouldn't it also be labelled as the MET if external to the CU too ?

Not that I am aware of.
514.13 applies

 

[Andy78]

Funny you should bring this up did the 18th Ed update yesterday and the tutor mentioned this figure and I asked where it was stated in the Regs which drew a blank look.

It's mentioned a couple or maybe three times in GN3 that I know of. None of the mentions relates to the resistance of the entire conductor along its length, although this an almost universally held belief.

 

[Deleted member 26818]

I take it PME conditions apply.

 

[Ian1981]

They are incorrect. Nowhere does BS7671 state or in any way imply that there is a 0.05 Ohm limit to a main protective bonding conductor. This measurement is intended to prove that the connection between the main protective bonding conductor and the extraneous-conductive-part is effectively made. It has absolutely nothing to do with conductor resistance.

So sick of hearing this rubbish especially from the apprentices we have at our company being taught false information from tutors

 

[TJ Anderson]

There is a calculation in the book based on the size of the largest protective device for bonding, I can't for the life of me remember where it is. I'll have a look for it later.

Adiabatic equation. If it's TN-S, 10mm may very likely be larger than what is required.

 

[TJ Anderson]

There is a calculation in the book based on the size of the largest protective device for bonding, I can't for the life of me remember where it is. I'll have a look for it later.

Adiabatic equation. If it's TN-S, 10mm may very likely be larger than what is required.

 

[Strima]

Adiabatic equation. If it's TN-S, 10mm may very likely be larger than what is required.

It’s not the adiabatic. This is specifically for bonding conductors not CPCs.

 

[TJ Anderson]

It’s not the adiabatic. This is specifically for bonding conductors not CPCs.

Yeah, 544.1.1
Except where PME applies, Main Protective Bonding Conductors shall not be less than half the csa of Earthing Conductor. You use selection or the adiabatic to size your earthing conductor......and then size bonding conductor from that, but not less than 6mm csa.