two dno supplies

[bigspark17]

I have a church with living quarters they used to be two seperate properties. Two dno tn-s supplied into either end of each building.! There is one boiler to do the lot, one water supply one gas supply. The boiler is supplied via one dno but main bonded via the other dno supply.! Any thoughts if there should be main bonding from both dno to where water rnters both properties? Any gaps ive left out ill try fill in!

 

[driverman]

I have a church with living quarters they used to be two seperate properties. Two dno tn-s supplied into either end of each building.! There is one boiler to do the lot, one water supply one gas supply. The boiler is supplied via one dno but main bonded via the other dno supply.! Any thoughts if there should be main bonding from both dno to where water rnters both properties? Any gaps ive left out ill try fill in!

Officially when the property became one, one supply should of been removed. i bet no one informed the DNO. In the past removing surplus supplies were.. whats that word? ohhh free! There might be a contribution cost now. Also electricians cost to marry up the 2 installations assuming 1 supply can take the total load.

 

[Engineer54]

So it's only the main water and gas supplies and a common boiler that connects the two DNO supplies then. Well the main water/gas supplies will be no different than these services supplying a row of houses. There should be stop cocks provided mind, to enable for the second building to be isolated from the first, ...and main bond accordingly...

The boiler shouldn't need additional bonding, ...it's already bonded via the water and gas pipes, as well as earthed via the boilers electrical supply...

 

[Richard Burns]

Provided that the two supplies are fed from the same incoming location then I would have said that the earthing systems of both supplies should be connected together; since they will already be connected to some extent by the bonding conductors it should be ensured that the two systems are adequately connected together.
If this is done then so long as any earth potentials entering the building are bonded to one supply they will be bonded to the other supply as well.
If the two supplies are not fed from the same incoming supply then there can be problems with potential differences between the two earthing points.
(I think theoretically that the "other" DNO supply would be introducing an earth potential into the property and should be bonded!)

 

[Knobhead]

It’s unlikely but it is possible for the supplies to be off two separate legs of a distribution network, or even two separate transformers.

What I would suggest is using a wander lead to test for a PD between the DNO earth points.
If there is a difference don’t link them. It only takes a volt or so to set up quite large circulating currents.