BigBuilder Posted January 23 Share Posted January 23 Hi i am at the start of my new house build, I’m applying for a new 3phase supply from SSE, I’ve filled out the forms and they are now asking the following …….. Important information: Please confirm Size of Generation required in kW or MW per phase. I don’t have an electrician onboard yet but I want to get this going ASAP due to their apparent ‘up to 7 month’ lead in!? ……..my question is what would be an appropriate figure to give them for each phase to answer this question? it doesn’t need to be accurate at the moment, just plausible. A bit of background, 4500m2 house, will have 2 fast car chargers, PV , ASHP, 2 dish washer etc etc , my chosen electrician will work out the final loads and sizing when they are on board , also I need a good supply to the garage for woodwork machinery etc in future. Thanks Link to comment Share on other sites More sharing options...
ProDave Posted January 23 Share Posted January 23 I would aim high, and quote say 80A per phase which is about 19 kW per phase or 57kW If they come back with a silly price, then talk about reducing the power needed. Link to comment Share on other sites More sharing options...
saveasteading Posted January 23 Share Posted January 23 49 minutes ago, BigBuilder said: 4500m2 house, Might that be 450m2 or 4500ft2? Link to comment Share on other sites More sharing options...
joth Posted January 23 Share Posted January 23 Dumb question but to check this isn't asking about export allowance? "Size of Generation required" seems a weird way to describe supply or import but maybe that's just me. Link to comment Share on other sites More sharing options...
Alan Ambrose Posted January 23 Share Posted January 23 The DNOs seem to delight in asking these questions in a stupid way ... or maybe they ask the same question whether you have a 3 bed house or are putting in a new blast furnace. The options in the real world (for residential) are likely 63A or 100A fuses (or maybe 80A as ProDave says). Which means 63A x 230V ~= 15 kW or 80A x 230V = 18 kW or 100A x 230V ~= 25 kW per phase. The smaller is probably fine - that's a lot of power. I have 63A 3-phase. Link to comment Share on other sites More sharing options...
BigBuilder Posted January 23 Author Share Posted January 23 3 hours ago, saveasteading said: Might that be 450m2 or 4500ft2? sorry yes of course Link to comment Share on other sites More sharing options...
BigBuilder Posted January 23 Author Share Posted January 23 3 hours ago, joth said: Dumb question but to check this isn't asking about export allowance? "Size of Generation required" seems a weird way to describe supply or import but maybe that's just me. yes I thought it was a strange way to phrase the question . Link to comment Share on other sites More sharing options...
BigBuilder Posted January 23 Author Share Posted January 23 4 hours ago, ProDave said: I would aim high, and quote say 80A per phase which is about 19 kW per phase or 57kW If they come back with a silly price, then talk about reducing the power needed. great, thanks Dave for input, ill try replying with that Link to comment Share on other sites More sharing options...
saveasteading Posted January 24 Share Posted January 24 23 hours ago, ProDave said: I would aim high, and quote say 80A per phase Is that the sort of capacity that would allow everything on at the same time and a bit to spare? Is there any sort of rule of thumb? Base level plus x/m2? Factor for new build or old? Link to comment Share on other sites More sharing options...
Alan Ambrose Posted January 24 Share Posted January 24 (edited) It's at this point I usually remind people that the point is to use less energy rather than more energy. Maybe add the max power of your car chargers and the heat pump and add 20%. It could be that the DNO doesn't care much anyway and there's no change in cost. Or you could ask for 100A and see what they'll give you. They won't change the size of the cable their planning to use, so it'll just be up to the marketing department. It's a bit like deciding between a 3L engine and a 5L. Yeah, more is better right? All your single phase mates will be on 25kW or less anyway. At 63A per phase you'll have twice that. Edited January 24 by Alan Ambrose 1 Link to comment Share on other sites More sharing options...
saveasteading Posted January 24 Share Posted January 24 Doing commercial and education projects , where our company took over from the clients' consultants, our electrician usually suggested that the mains supply be reduced, typically halved. The consultants apparently didn't want to hear of the project again, so estimated way to high. Other peoples' money. 1 hour ago, Alan Ambrose said: won't change the size of the cable they're planning to use, I didn't know that. Isn't a 3 phase cable rather different and more expensive? Link to comment Share on other sites More sharing options...
ProDave Posted January 24 Share Posted January 24 7 minutes ago, saveasteading said: Doing commercial and education projects , where our company took over from the clients' consultants, our electrician usually suggested that the mains supply be reduced, typically halved. The consultants apparently didn't want to hear of the project again, so estimated way to high. Other peoples' money. I didn't know that. Isn't a 3 phase cable rather different and more expensive? 3 phase cable is probably twice the cost (4 core cable vs 2 core cable) Another issue though is what infrastructure is in place already. We are near the end of a single phase 11KV spur. If I really really really wanted, or had to have 3 phase, then about half a mile of overhead 11KV line would need to be upgraded from single to 3 phase, and the transformer feeding our house would need replacing with a 3 phase one. You can imagine the cost of that would be completely stupid. 1 Link to comment Share on other sites More sharing options...
AppleDown Posted April 5 Share Posted April 5 On 24/01/2024 at 17:19, ProDave said: 3 phase cable is probably twice the cost (4 core cable vs 2 core cable) Another issue though is what infrastructure is in place already. We are near the end of a single phase 11KV spur. If I really really really wanted, or had to have 3 phase, then about half a mile of overhead 11KV line would need to be upgraded from single to 3 phase, and the transformer feeding our house would need replacing with a 3 phase one. You can imagine the cost of that would be completely stupid. Just had my quote through from SSE - £70k to get 3-phase to us. Clearly not going to pay anything near that. Anyone got any tips on how to get that reduced, or is it so prohibitively high that there’s no point going down that road…? Link to comment Share on other sites More sharing options...
Moonshine Posted April 5 Share Posted April 5 (edited) 7 minutes ago, AppleDown said: Just had my quote through from SSE - £70k to get 3-phase to us. Clearly not going to pay anything near that. Anyone got any tips on how to get that reduced, or is it so prohibitively high that there’s no point going down that road…? Do you really need three phase? My quote between single phase and three phase wasn't that different, so went three phase though don't need it. Have they quoted for the trench work from the road to the house as iirc its quite a distance. Edited April 5 by Moonshine Link to comment Share on other sites More sharing options...
garrymartin Posted April 5 Share Posted April 5 10 minutes ago, AppleDown said: Just had my quote through from SSE - £70k to get 3-phase to us. Clearly not going to pay anything near that. Anyone got any tips on how to get that reduced, or is it so prohibitively high that there’s no point going down that road…? It will depend on what the breakdown of the quote is. Can you provide that? Also, what did you ask for? Link to comment Share on other sites More sharing options...
AppleDown Posted April 5 Share Posted April 5 7 minutes ago, Moonshine said: Do you really need three phase? My quote between single phase and three phase wasn't that different, so went three phase though don't need it. Have they quoted for the trench work from the road to the house as iirc its quite a distance. Yeah that’s correct - from the main road and then down the lane. We don’t particularly need it - we were looking at as much solar as possible, but from what I can see it may be an issue with a higher capacity generated and not have 3-phase… Link to comment Share on other sites More sharing options...
Moonshine Posted April 5 Share Posted April 5 4 minutes ago, AppleDown said: Yeah that’s correct - from the main road and then down the lane. We don’t particularly need it - we were looking at as much solar as possible, but from what I can see it may be an issue with a higher capacity generated and not have 3-phase… I would ask them to revise the quote based on you doing the trench work on your land. Link to comment Share on other sites More sharing options...
AppleDown Posted April 5 Share Posted April 5 2 minutes ago, Moonshine said: I would ask them to revise the quote based on you doing the trench work on your land. That quote is with us doing the trench work 🙃 1 Link to comment Share on other sites More sharing options...
LnP Posted April 5 Share Posted April 5 I'm coming into this thread quite late, but this demand calculator might be useful. Link to comment Share on other sites More sharing options...
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