Connecting two earthing systems - PME on both - any implications of this?

Well - every one of the guys who have posted on this topic are way more knowledgeable than I so please do take on board what advice has already been given. They are streets ahead of I in knowledge. 


But I'd put this up for consideration and comment:


Considering that the metal pipe work, structural steel, gas supply etc etc is probably common to both incoming electrical services it all needs bonding somehow.............


See Table 54.8 page 203 in the BS7671 - I think that a 100Amp three phase supply would have probably have a copper equivalent cross sectional area of the PEN conductor of less than 35mm - so you'd need to interconnect the two METS with a minimum of 10mm bonding cable..........


BUT - Like I said - there was a very interesting article - I think it was in wiring  matters that addressed the problem of the length allowed for this bonding cable - I don't know how to post that article here. 


And I don't like the idea of using the cores of a SWA as a bonding conductor, (I assume you have a spare SWA already in place) I'd rather a dedicated green/yellow earth beteen the two METS - but if it is  labelled correctly and clearly I guess there's nothing prohibiting it's use. 


Please don't accept my answer on its own, because its the answer you want to hear..........


Kind Regards

Tatty

Well - every one of the guys who have posted on this topic are way more knowledgeable than I so please do take on board what advice has already been given. They are streets ahead of I in knowledge. 


But I'd put this up for consideration and comment:


Considering that the metal pipe work, structural steel, gas supply etc etc is probably common to both incoming electrical services it all needs bonding somehow.............


See Table 54.8 page 203 in the BS7671 - I think that a 100Amp three phase supply would have probably have a copper equivalent cross sectional area of the PEN conductor of less than 35mm - so you'd need to interconnect the two METS with a minimum of 10mm bonding cable..........


BUT - Like I said - there was a very interesting article - I think it was in wiring  matters that addressed the problem of the length allowed for this bonding cable - I don't know how to post that article here. 


And I don't like the idea of using the cores of a SWA as a bonding conductor, (I assume you have a spare SWA already in place) I'd rather a dedicated green/yellow earth beteen the two METS - but if it is  labelled correctly and clearly I guess there's nothing prohibiting it's use. 


Please don't accept my answer on its own, because its the answer you want to hear..........


Kind Regards

Tatty