Split phase v single phase advice needed

[John latimer]

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 5 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?

[billt]

My single phase supply is fused at 100A, which equates to 23kW. That's pretty common although the supplier may reduce the rating if there is an issue with the local grid capacity.

 

People generally want a 3 phase supply if they are going to run heavy duty machinery or want to install lots of PV.

 

A new house built with high standards of insulation should not need a large heat pump and shouldn't need a three phase supply, but it depends on what other large continuous loads you are intending to use.

[Marvin]

10 hours ago, John latimer said:

What warrants installing a split phase over just a single phase?

So the short answer is it depends what power you require for the property. 

 

For any of the more savvy BH members  you would need to share more info to obtain a valid opinion. My ASHP is max 16amp supply and replaces the night storage heaters of about 50amps so I have single phase supply. 

 

Good luck.

 

Marvin

 

Oh and you could always ask plumber why the thought of 3 phase came up. 

Edited October 12, 2021 by Marvin

[andy]

On the cable quandary, do what I did - terminate supply in a green box in the garden and have an isolator there with an SWA cable that goes from that into the house that you/your sparky can run.  That work?

 

Top tip for cable pulling, get a cable sock!