Electrical Supply to Multiple Flats

Typical single supply installation

One problem that is difficult to work out from either the regs or the on-site guide is how to correctly wire the supplies to a building that has multiple households within it, such as several flats in one house.

The usual situation is a house where the supplier's cable comes in to the supply head with it's 100A fuse. There's then about two feet of supply tails connecting to the meter, then about two feet of meter tails connecting (ideally) to the installation's isolation switch than about two feet of consumer tails connecting to the installation's consumer unit. All easy, and usually all on the same piece of wall next to each other.

The problem I faced was rewiring a building that consisted of a shop on the ground floor, and two seperate flats, one on the first floor and one on the second. The existing installation had all three installations fed from two meters in the shop cellar. One meter fed the shop through a two-way consumer unit. The other meter fed an eight-way RCD consumer unit in the cellar feeding the first floor flat, with a 45A spur feeding a coin meter in the second floor flat with a subsidary consumer unit.

Neither of the flats had access to the shop or, crucially, to the cellar. So, if a fuse went over the weekend, the tenants would be faced with waiting until Monday morning before getting any power back.

Rewiring the shop was fairly simple - standard comsumer unit next to the supply meter.

Ideally, each flat would have their meter inside the flat, next to that flat's consumer unit. The local supplier's supply conditions would not allow that. They insisted that the meters be on the inside of an exterior wall, in the cellar.

First, I pointed out that the flats had no cellar. They were flats above a shop!

Ok, they said, then the meters must be on the inside of an exterior wall at ground level.

I then pointed out that the flats had no exterior ground level walls. The flats are entered via a door at street level at the front of the building. This door opens into a ground floor lobby. The entire exterior wall is occupied by the front door!

I managed to get them to specify that the meters had to be within 5m of the public highway.

That's acceptable. The meters would be in the shared lobby, readable without requiring access to the flats themselves. If tenants were absent, the landlord could let the meter reader in without having to enter the flats. This is a common meter situation I've seen in tenament buildings in Scotland.

The next problem was sizing the cables to run 12m up the building to each of the flats' consumer units. There was no way I was going to buy 25m of 25mm2 singles! That's nearly 300 quid!

So, by trawling through the regs, the on-site guide, and pestering the local supplier to prise out required information, this is what I came up with. I hope it can come in useful for anybody else.