[Closed] 3 phase power

Firstly you'll need to see if there is a 3 phase supply available near to your property, there isn't always.

We wanted it for workshop equipment but there was only single phase available, it would have cost a fortune to do, and I don't think the electricity supplier would have done it as it would have been new overhead lines being installed and been a massive undertaking.

So we just used a single phase to 3 phase converter for when we needed to use the 3 phase equipment

I'm trying to arrange this at the moment, but getting a reply back from SP Energy is proving difficult. We're looking at installing 2 ASHP and a vehicle charging point, but can't even find out if there's a 3-phase supply near us.

3 phase is effectively 3 live inputs, the wine wave is offset for each phase. That means the cables are 3 lives and a neutral, very different to domestic single phase. As above will dependant on the availability of 3 phase in the street. We actually do have 3 phase as one of the phases blew years ago in the supply cable, every third house using that phase had no power for 2 days. Why do you want it?

I can see big demand for EV chargers but even for commercial premises it's not always viable.

For info Western Power are only installing 3ph on new builds now (thats been the case for the past two years).
You'll need a new 3ph cut out etc which should all fit in your existing meter box. No other changes to the internal wiring though (apart from the wiring to your 3ph appliances).

Additionally if 3 phase is available, I wouldn't change the existing wiring. Keep that as single phase, as you can just use one of the phases for your existing single phase DB and just put a new 3 phase DB in for any of the 3phase stuff.

We have 3 phase neutral and earth in our house but it's a former industrial building conversion. Only one of the phases is used as per a standard domestic install.
Will be handy for future car charging.

As above single to 3phase inverters are good for running industrial equipment.

Additionally if 3 phase is available, I wouldn’t change the existing wiring. Keep that as single phase, as you can just use one of the phases for your existing single phase DB and just put a new 3 phase DB in for any of the 3phase stuff.

Shouldn't you be balancing the load across all 3 phases though?

3 phase is effectively 3 live inputs, the wine wave is offset for each phase.

Do the appliances still use a normal 3 gin plug?

I had 3 phase put in c5 years ago with northern power grid. Cost 3k and had to come c200m up the road. The cost all depends what the magic computer says in some cases the power grid must bear some of the cost as a network upgrade. I think I got lucky. This was a new connection to the workshop. I don't know how upgrades work. Getting a quote was pretty straight forward but I think the are swamped with evs and ashps now.

@TheFlyingOx you should balance the phases. But if you were already on a single phase supply, then it should be balanced further down the system. E.g. your row of houses is on one phase, the next row on another etc. The DNO should be looking to see if the load is balanced.

If it was a complete new 3 phase installation without any existing single phase then it should be balanced equally across the 3 phases like you say.

If you can get a converter to make 3 phase from single - why no free lunch?

Is it that you gear up how much current is drawn. So 30amp 3phase needs 90amp into a converter to give 30amp on each phase?

On that thought, showing my total ignorance, how is 3 phase billed?

I looked at this when buying a new table saw and we've 3-phase to our nearest pole (about 5m away).

I discussed it with my middle son as he's a qualified Electrician working on industrial machinary etc. He told me to buy a single-phase table saw 🙂

I know TVs are getting big but 3 phase, how big is the screen? 😉

Nothing to add really but I live in what used to be a working farm and we have single phase to the house but a completely unused [i.e. dead ended] 3 phase to the barn next to the house.
We don't have an electric car but I've sometimes wondered about using the 3 phase to supply everything.
Is the only benefit the ability to to use higher power items such as car chargers?

Most residential streets have three phase running down the road and they just peal off alternate phases to each house. So adding the extra two phases will mean digging up a few metres of road. If you're in a remote building then less obvious.

Three black cables here:

[url= https://live.staticflickr.com/65535/52079575693_734cedcaf4.jp g" target="_blank">https://live.staticflickr.com/65535/52079575693_734cedcaf4.jp g"/> [/img][/url][url= https://flic.kr/p/2nm6rqR ]3 phase leccy[/url] by [url= https://www.flickr.com/photos/brf/ ]Ben Freeman[/url], on Flickr

Somewhere in Keswick where they're replacing the old gas main with a plastic one...

Is the only benefit the ability to to use higher power items such as car chargers?

Basically yes, there's a current limit per phase so if you have two of more phases you can double or treble the max power.

Our cottage in the Dales has two phases, one for the storage heaters and one for everything else. You can see the two phases entering top left...

[url= https://live.staticflickr.com/65535/50335979818_a9d2728d4c.jp g" target="_blank">https://live.staticflickr.com/65535/50335979818_a9d2728d4c.jp g"/> [/img][/url][url= https://flic.kr/p/2jG2481 ]Twin phase supply[/url] by [url= https://www.flickr.com/photos/brf/ ]Ben Freeman[/url], on Flickr

Larger industrial motors will be designed for three phase supply so commercial machine shops etc will run everything directly off three phase.

Basically yes, there’s a current limit per phase so if you have two of more phases you can double or treble the max power.

Gotcha, ta.

We went for 3 phase but were installing a new supply to a new build anyway, so over single phase it wasn't that much more money. The benefits for domestic come if you have specific requirements and in our case are not huge. I would like to install more PV than a normal domestic connection would allow, and 3 phase increases that limit. Our heat pump is a 3 phase one - we could just as well have fitted a single phase one but there's a small efficiency/performance gain with the 3 phase version IIRC. Our car charges on single phase at the moment. I will fit a 3 phase one when I fit a proper charge point. That will up the charging speed that but not so much as it would make a big difference to life since single phase charges it overnight anyway, but at a minimal cost difference from here (hardware is largely the same) I might as well; it's occasionally of real benefit.

Also, absolutely everything at our place is electric. Cooking, heating, car etc etc. So at times of peak draw we'd probably draw a fair bit more current than the average house.

On that thought, showing my total ignorance, how is 3 phase billed?

I had a commercial building with 3phase - each phase was billed separately, one phase powered lighting and sockets so was always more expensive than the other two.

I’m not a great fan of 3 phase for domestic premises as most of the equipment is still single phase and I do wonder if domestic electricians expect 3 phase in a house - I’m sure they can cope with it but don’t leave traps if you can avoid it.

That said, for multiple EV charging, heat pumps and larger PV or storage installations I can see the potential - although I’m presently having a 7.3kW PV installation done single phase (you just ask the DNO for permission).

Not sure about footflaps picture. Most (all? Trying to remember) LV three phase in the street I’ve seen is a single 3, 4 or even 5 core cable, not multiple single phases - but without going and having a look, I’ll take his word for it.

PS - other things being equal three phase motors vibrate less than single phase as the fluctuation of the power in each phase cancels out, so perhaps a heat pump might be quieter longer - more so if ground source as fans are pretty noisy anyway.

the wine wave is offset for each phase.

Do the appliances still use a normal 3 gin plug?

What's the third phase, vodka?

First things first, have you checked what's actually coming in to your house?

I got a daft quote of something like £35k from sse to lay 3 phase to my house (if I did all the required digging of trenches). I later discovered that the house actually already had three phase coming in, but only one was fused/connected. Ended up costing £50 to get the other two phases connected. Result!

Do the appliances still use a normal 3 gin plug?

More seriously,

My old office had a three-phase supply. The officey bits had regular 3-pin sockets variously wired to different phases. The server room and the network lab had in addition "Commando" sockets, big round blue buggers that you might have seen on camp sites. They were variously 16A and 32A.

It came in handy for us because the mains feed into the building was unreliable and power cuts were, if not common exactly then at least "too often." When it went we'd typically lose one of the phases, the other two would be fine (I don't understand the tech sufficiently to know why that might be). There were two Commando outlets on different phases behind the server racks, so if the power went to one I could just hop the cable across to its neighbouring feed and keep everything running.

Do the appliances still use a normal 3 gin plug?

Nice work

Also, is all 3phase in the UK the 'star' variety with a neutral?

Here in Belgland we also occasionally have the 'delta' variant with 220V between phases rather than 220 to neutral.   It's less common but if you have it most equipment needs some changes to work (I had to fiddle some connections on our oven for it to work ok).  Worse though is it is possible if the electrician in you house wires things wrongly you can have circuit breakers that appear to work but actually leave one of hte wires live :(.   This is why I always check even when things are switched off

Not sure about footflaps picture. Most (all? Trying to remember) LV three phase in the street I’ve seen is a single 3, 4 or even 5 core cable, not multiple single phases – but without going and having a look, I’ll take his word for it.

The 3 phase going to my barn is a single cable.

(all the feeds to our house where replaced about 8 years ago and while the engineers were here they asked is there was anything specific I wanted. I suggested taking out the 3 phase supply, as it wasn't used - they said I'd be daft to, "just in case".
Glad I listened to them!)

Most common

230V ph-earth, 400V ph-ph

But also

230V ph-earth, 460V ph-ph (split single, mainly rural)
230V ph-earth, 325V ph-ph (Scott wound, defunct I think)
Some weird 6 phase stuff in old mining areas
And probably some other stuff

If it’s for a machine install in a domestic situation then a single phase to 3 phase inverter is easy enough to fit to make it work, the downside of them is you lose some top end speed and torque of motors. Unfortunately it’s not a magic box, you can only get out what you put in.
Could be useful for EV charging though, would allow a 22kw unit over an 11kw

Not sure about footflaps picture. Most (all? Trying to remember) LV three phase in the street I’ve seen is a single 3, 4 or even 5 core cable, not multiple single phases – but without going and having a look, I’ll take his word for it.

I've seen both. They laid new twin 3 phases down our road the other year - three separate cables (or rather two sets of three).

[url= https://live.staticflickr.com/65535/52079870761_e73f6214ac.jp g" target="_blank">https://live.staticflickr.com/65535/52079870761_e73f6214ac.jp g"/> [/img][/url][url= https://flic.kr/p/2nm7X9e ]Twin 3 phase[/url] by [url= https://www.flickr.com/photos/brf/ ]Ben Freeman[/url], on Flickr

At LV? Interesting.

Which DNO?

ABC overhead of course, and triplex at HV, but I’d be interested to know who does separate single cores at LV.

You’re going to tell me it’s us now, and it will be. 😐

Edit - ahh, the photo answers the question. HV cables those.

Which DNO?

Central Cambridge, so Eastern I guess....

Did you some with Norweb years back and that was a single cable which looked like a pie chart - each core was a 120 degree slice.

Worked for Eastern as a student.

The Norweb / ENW one was a three core three phase cable - probably had a single circular earth sheath round the three cores.

Edit – ahh, the photo answers the question. HV cables those.

OK, didn't know that - assumed given the shallow depth it was just 415v.

The Norweb / ENW one was a three core three phase cable – probably had a single circular earth sheath round the three cores.

Yep, did have a small section as a paper weight, but think I've binned it.

I could get really boring in cables.  Probably best not to let me.

Son in Law is opening a restaurant and needed 3 phase. Cost them £6500 for a run of about 50 metres about 5 months ago.

Could be useful for EV charging though, would allow a 22kw unit over an 11kw

Worth noting that most EVs are limited to a lower wattage than that on AC. Mine maxes out at about 17kW (24A). However, 32A (so c.7.5kW) I think is the single phase norm so you still get to double that. 17kW is really nice and quick for a home charge point.

I could get really boring in cables.

Handy if you need a hole to thread them through.

Indeed

The wife works for Kia UK and their dealers are all upgrading to a standard suite of chargers for customers. Some of the connection bills from their DNOs are staggering (6 figures) if they're not close to a 3 phase supply or the local supply is maxed out.