clarification on earthing on a CU change

oldtimer · Jun 6, 2010

Hi all can you give me some clarification on earthing when changing a CU.

1. Do you have to upgrade the main earth to the water and gas pipework to 10mm or can you use the existing 6mm.
The reason I ask is that I am getting conflicting reports saying yes you do o no you dont ? .

2. Can you loop say a main earth from the water pipework to the gas pipework.

3. Main earth from DS should this be 16mm or can you use 10mm.

ezzzekiel · Jun 6, 2010

you always will get conflicting views.
personnaly i would always upgrade unless it is too difficult and customer dont want upset, however as you would be responsible then you would need to be able to prove it was suitable if needed and in any case only on tns or tt and min 6mm would be allowable.

main bond not main earth can be one fom gas to water as long as its continuous (one unbroke length)

same as above for main earth providing you can prove it then as the electrician its your decision your name.

SirKit Breaker · Jun 8, 2010

General rule of thumb is and as i understand it.

Main earth cable must be minimum of 50% cross sectional area (CSA) of your meter tails. Bonding cables must be minimum of 50% CSA of your earth cable so :-

25mm supply tails
16mm main earth connection
10mm main bonding
6mm equipotential.

This is of course decided by the rating of the cutout fuse, and assumes 100amp.

At 80 amp it is compliant if

16mm supply
10mm
6mm
4mm all as above.

It is good practice to upgrade to requirements for a 100amp cutout fuse as this makes it future proof for now.

If it isnt practical or possible to upgrade any bonding then a 10mm main earth connection, and 6mm to water and gas etc is acceptable but must be noted on the certs and a clear reason why an upgrade was not carried out.

Hope this helps,

Cheers..............Howard

Spudnik · Jun 8, 2010

you can always crimp the main bond before the gas pipe, loop through gas clamp and then on to the water, providing it is suitably sized of course.

oldtimer · Jun 9, 2010

Thanks SirKit
This is exactly what I thought but was getting confused with regards by the main earth should not be less than half the size of the main supply cable ? surely this should read dependant on the size of the main fuse.

For example a flat or house has a 60 amp supply fuse but the spark who fitted the existing board or the supplier who replaced the meter and was nice enough to replace the old VIR cable on the consumer side put in 25mm tails because thats all they had at the time no problem their but does this mean you have to comply and upgrade the earth to the gas/water from 6mm to 10mm my reasoning here is that when you are quoteing to replace a CU then upgrading to 10mm can impact on the cost and time to do the job.