2 service heads supplying in same room ?!

[Paul Maughan]

Hi,
So I Carried out an EICR at a business park. which was originally 2 buildings with 2 separate metered supplies, now the buildings are joined together. It’s gets interesting as some of the rooms are now fed from 2 different DBS from different service heads! I’m aware this is very wrong, it should have 1 point of isolation and there’s risk of different potentials being introduced somehow. What would a reasonable solution be to suggest to the client ? Ideally I imagine it would be to lose a supply and refeed 2nd DB from same supply/section board or similar but the supplies are only 100a and wouldn’t be big enough without upgrade to supply, this would start getting very expensive and the incoming supplies are about 40 metres away from the building in a little hut ! I can rework rooms so cross over circuits are removed, cross bond between both buildings so at same potential and put big notices on both DBS is what I’ve thought up so far ? Any help greatly appreciated !

 

[westward10]

You need to consult the DNO. Different providers have differing opinion, linking the two earthing systems together is one however TN-C-S systems may in some cases negate this. This is outside the scope of BS7671 so I would consult the service provider.

 

[R-fur]

If there are two DNO meters, your customer may be paying two standing charges for the meters, if so you may have a financial incentive for him to do remedial work.

 

[GBDamo]

Are the two supplies off the same phase?

If so, can you trust the DNO to keep it that way?


Had a similar where two units had been partially joined before the company went bust . No ceilings, not plastered. Circuits run from two supplies all over the shop.

Was tasked with seperating them. In the end diconnected from the mains isolator for both then took an angle grinder to all circuits and rewired.

Each was really simple to rewire whereas being 100% sure they were fully independent would have been a pain.

 

[Paul Maughan]

I spoke to both NAPIT and local DNO today. both supplies are earthed by DNO (it’s 3p+N supplied from pylons) at same point outside the building so should remain at same potential. I’m going to just alter the wiring so the rooms are all on one DB or the other and put big notices on both DBS stating it’s dual supply to the building. Thanks for all the input peeps, greatly appreciated ! One day I hope to be able to answer someone else’s questions ?
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Are the two supplies off the same phase?

If so, can you trust the DNO to keep it that way?


Had a similar where two units had been partially joined before the company went bust . No ceilings, not plastered. Circuits run from two supplies all over the shop.

Was tasked with seperating them. In the end diconnected from the mains isolator for both then took an angle grinder to all circuits and rewired.

Each was really simple to rewire whereas being 100% sure they were fully independent would have been a pain.

Cheers mate
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If there are two DNO meters, your customer may be paying two standing charges for the meters, if so you may have a financial incentive for him to do remedial work.

Yes that is true but it’s metered as 2 separate businesses for the billing but in one building

 

[R-fur]

Surprised the DNO will leave two supplies into one premise. Normally they go to great lengths to prevent this as it could result in one of their services being backfed.
I understand that you say it is two separate busneses in one premise so they want separate billing, but it is often cheaper to have one official meter and then submeter to split consumption between the business units. If you can get a look at a couple of the bills there is often a standing charge then so many units at a high rate then the rest of the units at a less high rate. By combining the bills you only pay one standing charge and one lot at the high rate. Five minutes with some bills and a calculator and you can normaly work out the annual savings, that may or may not justify spending money on the system.

 

[Paul Maughan]

Surprised the DNO will leave two supplies into one premise. Normally they go to great lengths to prevent this as it could result in one of their services being backfed.
I understand that you say it is two separate busneses in one premise so they want separate billing, but it is often cheaper to have one official meter and then submeter to split consumption between the business units. If you can get a look at a couple of the bills there is often a standing charge then so many units at a high rate then the rest of the units at a less high rate. By combining the bills you only pay one standing charge and one lot at the high rate. Five minutes with some bills and a calculator and you can normaly work out the annual savings, that may or may not justify spending money on the system.

Tbh the DNO supplies are actually 50metres away from the building in basically a small brick cupboard. I did consider just running off one supply and sub metering at the DBS , But it’s not big enough for demand. It wouldneed DNO supply upgrading and also a bigger sub main Under the car park, or a bigger outbuilding and a panelboard in it. I agree about the standing charge but I don’t think the client will want to put grands into it as it’s up for sale and just wants a cert for it . Thanks for the advice though, greatly appreciated

 

[R-fur]

Ok, so if it is two submains coming from one metering point, would it be possible to run the two submains in parallel then split and submeter at the end?
Sorry, I don't know the layout of your job so I will shut up now.

 

[Paul Maughan]

Ok, so if it is two submains coming from one metering point, would it be possible to run the two submains in parallel then split and submeter at the end?
Sorry, I don't know the layout of your job so I will shut up now.

Hahaha yep it’s a bit of a strange one, It’s 2 sub mains from 2 meters /2 supplies into one building

 

[ipf]

Tbh the DNO supplies are actually 50metres away from the building in basically a small brick cupboard. I did consider just running off one supply and sub metering at the DBS , But it’s not big enough for demand. It wouldneed DNO supply upgrading and also a bigger sub main Under the car park, or a bigger outbuilding and a panelboard in it. I agree about the standing charge but I don’t think the client will want to put grands into it as it’s up for sale and just wants a cert for it . Thanks for the advice though, greatly appreciated

I agree with what you say in #5. If you're certifying it (prior to sale) you want it right from your point of view. Just give a full explanation with the certificate to clear yourself, with sanction from DNO.

Not the same.....but I remember a couple of jobs a good few years back when upgraded 3ph supplies were needed. New supplies were installed but, even after notifying DNO, the existing, both in different positions, were never isolated and left live with meters removed.