Quick question SWA cable and economy 7 supply

[ProDave]

First fixing a new build "eco house" and the builder has dropped me an interesting little problem.

The house is on a private park. So the "DNO" is the park owner. The way they do things is the meters and cut outs are in little boxes dotted around the park. So SWA from "their" supply to the CU in the house.

Trouble is it's electric storage heating (yes I know where does that fit into an eco house?) but the dual rate meter and time clock will be in the meter hut.

So that's two supplies from the hut to the house.

Trouble is, the builder has installed ONE SWA cable, that's burried in the concrete floor and foundations and would be a big PITA to add another one.

Thankfully it's a 3 core SWA.

So can anyone see a problem (or a reg that prevents) me using one core for neutral, one core for permenant supply, one core for off peak supply and the SWA for earth?

Off peak supply is minimal, just two small storage heaters.

Supply as far as I can establish is TNS, but nobody can tell me that for sure.

 

[NozSpark]

What size cable, how long, what size protective devices???

If you could do it youd have to size everything to the neutral csa

 

[batty]

Will the armour be adequate for any fault currents probably not for tncs maybe you could TT house to get over that?

 

[ProDave]

It's only a 40A supply, BS88 fuse as far as I know in the meter hut, 10mm SWA about 15 metres long.

 

[Evans Electric]

On the face of it I can't see a problem with sharing the neutral , your just adding , say 4 KW in the night , through a different meter .

There used to be a lot of SWA cables with reduced size neutrals in them , may have come about during WW2 to save resources , just guessing .

 

[Sidewinder]

As above, perhaps you should get the developers electrical design engineer on the phone to confirm the specs though, as they are now the supplier under ESQCR you will find.

 

[steptoe]

how many storage heaters and what size?

is there a water heater too?

how much diversity can you really apply to the heaters?

in the real world, prob be OK,

but on paper, perhaps not.....

TT sounds a good idea for the sheath issue, and not just because I prefer it, it may help a LOT in this scenario.

 

[ProDave]

Two storage heaters, One 2KW input, not seen the spec. for the other one.

Gas water heating (which also powers the shower) and gas hob. There's not even any oven of any sort in this house, just a free standing microwave oven.

Other means of heating is a wood burning stove.

So overall, I expect loads to be pretty small and in the real world I can't see any issues. I was just concerned there might have been a reg I had missed preventing a shared neutral for the peak and off peak supplies.

And yes I think a TT earth might be a good option.

 

[Doc Hudson]

In the real world in a domestic property the off-peak uses the same neutral as the daytime power, as it all comes up the same cable into the house. It is an academic argument as to where the lives split should the neutral also split? Interesting question Dave!

Doc H.

 

[Adrian]

just a thought why not fit time clocks to the night stores and supply them off the normall tarrif so when the tarrif switches to e7 say at 24.00 the night stores come on.

or fit a time switch and contactor before the off peak board because at 24.00 hrs all the consumer units are on cheap rate anyway

 

[ProDave]

just a thought why not fit time clocks to the night stores and supply them off the normall tarrif so when the tarrif switches to e7 say at 24.00 the night stores come on. or fit a time switch and contactor before the off peak board because at 24.00 hrs all the consumer units are on cheap rate anyway

I thought about that, and that's certainly what I would have done if the builder had only fitted 2 core SWA.

The only issue might be if they do it the "old way" where there are two physically separate meters, and ONLY the off peak circuits got the cheap rate (used to be called white meter or something). Since this is a private supply arangement, anything could happen.

It will be about 2 weeks before the job is finished and it goes live, I'll try and remember to report back exactly how the supply is aranged.