Single phase vs 3 Phase Supply - Cost Differences?

pmartin86

Afternoon All

The house I moved into about a year ago has a Three-Phase supply fitted, this was for a previously disabled occupant (lift, hoists, therapy room etc) and is not "needed" by us. We are having work done now (replacing some circuits and having Solar Panels fitted) and it has been suggested that we could drop it to single phase. Before I get to into this, I'd like to know if there are benefits / drawbacks as it will add about £500 to the work.

1. Is there a difference in cost to me for 3 phase over single phase? Higher standing charge, cost per KWh etc?
2. Is there any positives or negatives to the general household supply I need to think about? Will it affect stability? power usage etc?
3. Any additional safety concerns?
4. Any other +ve / -ve to keeping vs removing?

Thanks in advance
Paul 

ComicGeek

Provided that it's on a domestic tariff (and not a commercial tariff) it shouldn't cost you any more to run. You'll just pay for what you use, even if you're only running single phase loads in the house.

I definitely wouldn't pay to reduce it down to single phase! Can't see any benefit in doing that. 

Would also enable you to fit larger PV system without DNO approval, as you can install 3.68kWp per phase without prior permission.

Would be great in charging electric vehicles in the future, and also future proofing for heat pumps, lift etc in the future.

DullGreyGuy

Its useful if you have a high powered device that can use the multiphase input. We have a device that has a very high amp requirement on single phase which means a massive thick cable but much more reasonable when its split over three phases. The manufacturer also says life expectancy of it is better on a three phase supply

pmartin86

Thanks both.

@ComicGeek - Yes, defiantly a domestic tariff so that's good to know - I've had a good look around and googled what I can (I've got enough knowledge to make educated guesses about electric installs, change faceplates and switches etc, but nowhere near enough to be confident in the bigger bits) and it seems like the 3 phase comes in, hits the "main" fuse box and there are various "breakers" in there that are 3 phase (3 x bay trip switches) that run to a defunct therapy pool and the lift - i assume these 2 items are the "3 phase" and everything else is a single breaker (standard upstairs lights, downstairs light, upstairs sockets etc etc) which I assume is "standard" single phase.

Would you mind explaining how the PV system would work? My chosen installer has said they will do the application to the DNO (Western Power in my case?) as we are looking at a 7.7wkh system (20 panels with a 5kwn battery) - If we keep 3 phase does that mean this isn't required?

@DullGreyGuy - Yes, I had considered longer term, I've had various hobbies in the past with woodwork / metalwork etc and can see in the longer term building a workshop for a "forge" (Had a couple of lessons way back when, seems like a wonderful hobby) so being able to "potentially" run a power hammer / press / welder etc would probably be "nice to have" - Though if I'm being realistic, this is probably a decade or 2 down the line when the kids are old enough to start buggering off and I can start looking at winding down for retirement!

So, all in all, as long as 3 phase isn't going to "cost" me anything, or present any drawbacks, ill probably just stick with it.

fenwick458

I would imagine there probably is a cost difference for a single phase 100A meter and a three phase 100A meter from your energy provider, best person to ask is them.
I've seen plenty of ex industrial buildings that have a three phase supply, but only a single phase meter connected to one of the phases as thats typically all thats needed in a domestic house. I can't think of a need for a 3ph supply so thats what'll probably happen, they won't completely remove the other 2 phases, just fit a different meter to one phase only.

ComicGeek

pmartin86 said:

Would you mind explaining how the PV system would work? My chosen installer has said they will do the application to the DNO (Western Power in my case?) as we are looking at a 7.7wkh system (20 panels with a 5kwn battery) - If we keep 3 phase does that mean this isn't required?

You can install generation capacity of 16A per phase without prior permission and then submit a G98 application within 28 days of installation. For most domestic properties they would only have single phase, so 16A = 3.68kWp. In your case you have 3 phases, so 3.68 x 3 = 11 kWp. You would need to use a three phase inverter though, have a three phase consumer unit, so that it exports back through the meter across 3 phases not 1.

So the 7.7kWp system with 5kWh battery wouldn't need DNO approval. The DNO approval process isn't quick, a few recent ones I was involved with took 12 weeks, so always good to not have to do it.

I wonder if they aren't used to 3 phase systems, and just want to use single phase inverters - in that case you would be installing 7.7kWp on one phase, and exporting out an unbalanced load on only one phase, so would need DNO approval. I can't help thinking that the DNO response to this should be to install a three phase inverter.

FreeBear

ComicGeek said: I wonder if they aren't used to 3 phase systems, and just want to use single phase inverters - in that case you would be installing 7.7kWp on one phase, and exporting out an unbalanced load on only one phase, so would need DNO approval. I can't help thinking that the DNO response to this should be to install a three phase inverter.

A three phase inverter should be a lot more reliable than a single phase unit of the same rating - The output current will be spread over multiple components, reducing the stress they are under, and therefor, less likely to fail. The downside is a three phase unit will be a little bit more expensive, but only you can decide if the potential increase in reliability is worth it - The reduced paperwork with the DNO might swing it for you though.

Personally, I would jump at the opportunity for a three phase supply if it wasn't going to cost extra - I could then run my adult big toys without worrying about tripping the breakers..

Risteard

ComicGeek said:

pmartin86 said:

Would you mind explaining how the PV system would work? My chosen installer has said they will do the application to the DNO (Western Power in my case?) as we are looking at a 7.7wkh system (20 panels with a 5kwn battery) - If we keep 3 phase does that mean this isn't required?

You can install generation capacity of 16A per phase without prior permission and then submit a G98 application within 28 days of installation. For most domestic properties they would only have single phase, so 16A = 3.68kWp. In your case you have 3 phases, so 3.68 x 3 = 11 kWp. You would need to use a three phase inverter though, have a three phase consumer unit, so that it exports back through the meter across 3 phases not 1.

So the 7.7kWp system with 5kWh battery wouldn't need DNO approval. The DNO approval process isn't quick, a few recent ones I was involved with took 12 weeks, so always good to not have to do it.

I wonder if they aren't used to 3 phase systems, and just want to use single phase inverters - in that case you would be installing 7.7kWp on one phase, and exporting out an unbalanced load on only one phase, so would need DNO approval. I can't help thinking that the DNO response to this should be to install a three phase inverter.

Just to be pedantic, there is no such thing as a "three-phase consumer unit". A "consumer unit" is a particular type-tested single phase distribution board.

DullGreyGuy

FreeBear said:
Personally, I would jump at the opportunity for a three phase supply if it wasn't going to cost extra - I could then run my adult big toys without worrying about tripping the breakers..

A TikTok video the other day joked that a girl in her teens has a toy powered by a pair of batteries but a woman in her 30s has one mains powered... not sure what age you move up to a three phase version!


Our device had 3 heating elements and looking at the wiring diagram in three phases each phase heat one of the elements whereas in a single phase setup obviously they all get linked and powered by the one. Was never sure why the manufacturer said the elements last longer on a three phase setup, after all they will be heated to the same temp irrespective and there was no claim of a more even heating or such to suggest one element gets hotter on a 1 phase before the juice runs out for the last element (thinking in very non-electronic terms)

FreeBear

DullGreyGuy said:

FreeBear said:
Personally, I would jump at the opportunity for a three phase supply if it wasn't going to cost extra - I could then run my adult big toys without worrying about tripping the breakers..

A TikTok video the other day joked that a girl in her teens has a toy powered by a pair of batteries but a woman in her 30s has one mains powered... not sure what age you move up to a three phase version!

When you can afford a Bridgeport, Haas, or Vicmarc. Gender doesn't come in to it.

pmartin86

Thanks for all your comments everyone - Defiantly learning a lot more about things which is really helping the decision making - I'll pass the idea of a 3 phase toy onto the wife and get back to you @FreeBear

I've spoken to the installer and they mentioned a 3 phase inverter would be a better idea and sticking with the 3 Phase supply, so all good there, one of the reasons I (we) like the company is they have always been quite honest in the past when "questioned" and are happy to explain or change their initial thoughts without getting "defensive" over it like some other might. So, all in all, looks like I'm keeping 3 phase, getting a different inverter and ready to get rolling. Should get them installed just in time for the dark and dreary winter months!