2 supplies to single building

[oscar21]

We are refurbishing an empty commercial building at the minute and I don't do commercial stuff day in day out so not entirely clued up on everything. The building is one property, central entrance hall with two big offices left and right from the hall way, the hallway though has two meter cupboards and two incoming 3 phase supplies, one has a poly-phase meter on it where the dis board is that runs everything and the other has a single phase meter connected to only one of the phases with the outgoing meter tails terminated in an adaptable box and not used.

The client wants to rent the two offices out as separate units each with their own electric bills, providing the second incoming supply is actually commissioned and can be utilised is there a problem with two sets of incomers into essentially the same building, I'm thinking maybe a difference in earth potential the two supplies will end up being bonded together due to the metal frame in the building anyway.

 

[westward10]

Yes this is possible. Main protective bonding may be an issue with TN-C-S however the normal practice would be to bond the earthing systems together if services are shared or if separate and in simultaneous contact. Who pays for the communal area power?

 

[oscar21]

Yes this is possible. Main protective bonding may be an issue with TN-C-S however the normal practice would be to bond the earthing systems together if services are shared or if separate and in simultaneous contact. Who pays for the communal area power?

Thats the problem, the entrance bit is divided into one hallway, two little toilets and two little kitchens, so one kitchen and toilet will have to go one one board and the other kitchen and toilet on the other dis board.

The other problem I see is someone who thinks he is ultra cautious when doing electrical work will find (one of) the main panels and switch the main switch off because he never takes any chances and then go to work on say the hand dryer or something and get quite a nasty shock, I mean why would you test if its still live if you ditch the whole building.

 

[westward10]

Splitting the toilets and kitchens isn't a problem nor is worrying about anyone working on it in the future, safe isolation is their problem. What are the earthing systems?

 

[oscar21]

I'm guessing both TNC-S, they are fairly modern 1361 3 phase supplies, both similar, the building is about 30 years old.

 

[snowhead]

The other problem I see is someone who thinks he is ultra cautious when doing electrical work will find (one of) the main panels and switch the main switch off because he never takes any chances and then go to work on say the hand dryer or something and get quite a nasty shock, I mean why would you test if its still live if you ditch the whole building.

You'd still test even if the DNO were outside and you could see the incomer had been dug up and cut off.

If they'd turned the supply off and expected everything to be dead then they'd be surprised when they found the toilets lights came on.

 

[oscar21]

You'd still test even if the DNO were outside and you could see the incomer had been dug up and cut off.

If they'd turned the supply off and expected everything to be dead then they'd be surprised when they found the toilets lights came on.

Its called confirmation bias, even though you can see something with your own eyes your brain refuses to accept it because its so sure it can't be possible. Mentour pilot on youtube is always going on about it when he dissects plane accidents. If you are absolutely convinced the power is off then you will still touch the cables even though a vols stick might be glowing bright red, it will look off to your brain.

 

[littlespark]

Same as a block of flats Several supplies into one property?

There may be an issue that the single phase is an older supply and is cut off in the road when the 3ph was put in…. Supplier should be able to confirm.

 

[James]

We used to have a large building that had 2 supplies, in different ends of the building to each other.
however their was no deviding line, each supply ran equipment in all areas of the building

we did put a notice next to each main incomer warning of 2 supplies with a site map showing the location of the other one.

this was more for the fire brigade or any other emergency service that may need to isolate the building in an emergency than for an contractors coming in.

 

[westward10]

Biggest issue is the earthing systems.

 

[EricMark]

Where I work it was at one point start up units, and as a result there are I think 4 x 3 phase supplies, the cost to remove them was silly, so we are now using three of them, one general for building, one for an EV charging point, and one for a compressor.

We have considered the TN-C-S supply, but the metal of the building and the 8 miles of railway track are likely such a good earth the only worry with loss of PEN is can the earth bonding take the current, and the supply transformer is not that big, so highly unlikely to cause a problem.

It does seem the DNO does not like two supplies to one building from different transformers, but if all from the same transformer then no real problem.

 

[mhar]

I recently had similar but my 2 supplies were from different transformers going into different ends of a long property divided in two. Western Power were ok with this and with it being PME as long as the two sections were completely electrically seperate. Unfortunately they shared the same oil boiler and all pipework was in copper. A plumber inserted plastic couplers in the places where it was obviously connected (the idea being that these would then be doubled up and distanced if successful so that the two different earthing systems couldn't be touched at the same time) but we still had continuity between the two buildings.
The situation was then referred up to the senior protection officer in Bristol (I believe) who would then only allow us to have tt systems on each with upfront 100mA time delayed rcds. Rodding was a nighmare on one of the sides (except for when going through the drain!!) so they sent out a digger with an operator so that he could use the pneumatic hammer that they attach to the digger to drive in rods for me.
We had just spent nearly 30k on a new installation of a 315kV 3 phase transformer and allowed them to lay a 185? mm wavecon cable from our transformer to an existing pole for them to connect in the event of a failure of that part of the system