Bonding of main cupboard

grandfortune said:

HI all,

just need clarification on bonding of a mains cupboard please.

Setup is
Mains cupboard 2mtrs wide and 6mtrs long
10 cutouts feeding 10 flats , has meters then tails to cutout then 25mm concentric to each flat

5 water tanks are in there and cables from flats feed the immersion heaters, cooper pipes from tanks then above ceiling all plastic, also plastic feed coming in.

lighting and power in main cupboard off 5x5 split board all rcd, with PV inverter, and aerial boosters.

company has come in and said all the cooper needs bonding, its all plastered now so I think they might be assuming that all the installation is in copper but its not, I haven't bonded as I usually don't need to , but think that the cupboard is so narrow you can touch the cutouts (non RCD) and the copper of the water tanks, just need some guidance please .

Cheers
Grand

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May help you

is this a new building or old .

What parts are they suggesting you need to bond? Is there gas in the flats?
Have you run a split concentric submains or just concentric?

Who and what are "company"?

Murdoch said:

Who and what are "company"?

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What he said^^^^^^^

Murdoch said:

Who and what are "company"?

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Also what testing or regs have they quoted to say it needs bonding?

I think by chance they may be close to being right. Essentially the water tanks and exiting copper pipes are almost certainly not capable of introducing an earth potential. However if the flats have been designed as individual installations then, because of the wiring from the flats coming back into a communal area, a fault potential from one of the flats could be introduced into the cupboard via the immersion heaters. This is the uncommon situation of an extraneous conductive part introducing a potential that is not earth potential. (extraneous to the cupboard, not the flat)
Working against this is that the flats earthing systems are all commonly connected via the incoming earth and (assuming you meant split concentric rather than a non compliant concentric) at bonding suitable sizes so the fault potential will transfer to the other flats anyway, however only via the volt drop over the immersions cpc which may mean an elevated voltage when referenced to the other tanks.
All this does depend on whether the design has been done as one conjoined installation or ten different installations, though if there is no other bonding it is difficult to define and it is a bit blurred by having the flat circuits all coming back to the common area.
It is a bit like if you installed a metal clad socket from your CU into your neighbours house and both were fed from the same supply, a fault on that socket could mean a shock risk to the neighbours even though the socket is earthed back to your house.

company is from surry, flats are fed from 25mm split concentric, havent gone into details on the regs or why yet, i have a contact number and just wanted to clarify things.

Cheers
Grand

no gas in the property

grandfortune said:

company is from surry, flats are fed from 25mm split concentric, havent gone into details on the regs or why yet, i have a contact number and just wanted to clarify things.

Cheers
Grand

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Please answer the question properly ..... what does this company do? Why are they there?

If there is no gas at the property and therefore I assume electric heaters not radiators, then overall with the interaction of all the circuits, aerials and PV being mixed together and assuming there are no large exposed structural metal parts that are not common to all flats then I think that perhaps the whole structure can be considered as one installation. It does not seem sensible to try to claim that each flat is an enclosed area not interacting with other flats. Therefore each tank is an exposed conductive part as it is part of "the" electrical installation and requires earthing, which is presumably in place.
I did do a calculation with some random figures and came up with one tank being 140V above the others in a fault situation, but I cannot see how this would differ from a metal light fitting in a house above an immersion tank when the immersion fails to earth.
Just some thoughts.