Split phase v single phase

[Lats]

First and foremost I am not an electrician, I just need some simple advice about split phase or single phase supply. I’m building a 4 bed house and have laid a service duct under the block and beam. I have received a quote from SSE to install a split phase electrical supply but they don’t want to run their cable as I had planned. Which means I’ll have to dig up some of the block and beam and it all seems a massive pain in the backside and I don’t really understand it. Here is the what SSE emailed me:

‘’I see on your plan that you have marked a yellow cable route that goes under the building and the across to the cut out / fuse position

Due to the distance to the supply point we need to have some mains cable installed and then a service off that – we wouldn’t install mains cable under or through a building or put it into a duct as that de-rates the cable and also makes it vulnerable to overheating, that is why the 95 wavecon cable should go into an open trench so that any heat is dispersed into the ground

If you look at the plan provided with the quote you will see I have therefore marked a route from the pole then underground between the U shaped area of the building and pot end that with a 20 meter 3 x 35 service off the end. The service can go in a duct from the pot ended 95 wavecon cable to the cut out position inside.’’

So my question is, although my plumber advised split phase because of the air source heat pump, do I really need it? What warrants installing a split phase over just a single phase? How much electricity is too much for a single phase?

 

[ProDave]

A picture would make it clearer, but this sounds normal to me.

They use a large cable, in this case 95 square mm for most of the run, that is laid in an open trench, not in ducting.  Then just before it goes under the building there is a potted junction in the ground and the last bit of thinner, 35mm cable goes under the building in ducting to the service head.

So you don't need to dig up your block and beam floor, that bit stays in the ducting you have already laid.

Chances are you only need single phase, but as 3 phase is available I would take it, it future proofs you for e.g. multiple EV charging points.

 

[binky]

In short, 3 phase means they can use a smaller cable. Useful to have 3 phase as per reasons stated by ProDave. It also means if you want to go green and put solar panels in/ a wind turbine, you can have a much bigger array.

 

[steptoe]

He's talking about split phase, not 3 phase, 

tbh, I didn't think split phase existed anymore, except on the very odd existing old install, a bit like 2 phase, I don't think you can get that anymore either. 

@Lats is this a UK install,? 

 

[Lats]

Thank you, appreciate it. 3 phase is not an option because we are rural and it costs over £15k. Yes split phase is what we have been quoted for and we are based in England

 

[Andy™]

still find the odd split phase supply still in use in ural areas around here, plenty areas where 3 phase isnt there

depends on how much load you plan on using, your electrician would be best to decide that, not a plumber. single phase may be an option, split phase would give you a bit more