UK Sub Main Armouring Earthing Question Combined CPC and Main Bond

[John-]

Hi

I have reviewed a few posts around this subject, but my question is not covered. I know that the Submain Earth has to be sized on the DNO incomer, not on the submain to the external building itself. My question is if I need two main bonds in the submain building, for example one for ground fed metal pipe for water and ground fed metal pipe work for gas, does that mean the equivalent earth sizing of the armoured / extra conductor in the armour, must also be sized to take account of 2 x 10mm or just one 10mm (example assumes TNCS with 25mm Line. Or is there something in the regs that assumes one fault to earth only and not multiple?

Thank you.

John

 

[westward10]

No you only need to account for one csa.

 

[telectrix]

what size are your SWA conductors?

 

[John-]

No you only need to account for one csa.

Thank you for coming back. Where is that backed up un the regs please?

 

[John-]

what size are your SWA conductors?

sub-main = 16mm, DNOs = 25mm.

 

[telectrix]

as long as the SWA is 3 core. the cpc is adequate for bonding, the steel armour is superflous. but must tbe earthed, as you know.

 

[westward10]

Thank you for coming back. Where is that backed up un the regs please?

It is no different to have multiple main protective bonds at a main earth terminal but only a single earthing conductor supporting it.

 

[John-]

as long as the SWA is 3 core. the cpc is adequate for bonding, the steel armour is superflous. but must tbe earthed, as you know.

on one specific armouring is used (TPN 4 core cable only) for CPC (installed a long while ago). There is another sub-main in this building which does use a core for CPC. Same size too. Was thinking of joining both armouring and the SP CPC and creating a sub MET in the building and then running the main earth from this Sub MET so shared across two sub-mains for both supplies. I should state that the Single Phase board is supplied via a manual change over switch to be fed via generator in the event the site mains fail.

 

[Strima]

It won't be a Sub MET (MAIN Earth Terminal), it would be an EMT (Earth Marshalling Terminal). Common practice on a lot of sites to use this method.

 

[John-]

It won't be a Sub MET (MAIN Earth Terminal), it would be an EMT (Earth Marshalling Terminal). Common practice on a lot of sites to use this method.

Thank you. By the way what is the best way of knowing the exact size of the DNOs supply conductors? Would they know if i called or have i got take it apart and measure?
Thanks.

 

[John-]

It is no different to have multiple main protective bonds at a main earth terminal but only a single earthing conductor supporting it.

didn’t think about like that but yes you are right. Thank you.