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Should I have 3 phase supplied to my house?

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choochoo_baloo30/05/2019 00:38:58
206 forum posts
28 photos

Hello chaps.

My home workshop build is nearing completion, and thoughts have turned to the supply for my 3 off, 3 phase machine tools.

I've contacted Transwave about their converters. Seems a good option.

Someone suggested getting a 3 phase supply quote from my power distributor (Scottish Power). He reckoned it would be comparable to the total cost of phase converter + electrician wiring to the out building.

Any advice appreciated.

Edit: Just discovered that the jargon for the company operating the power network after the National Grid is "Network Operator" e.g. Scottish and Southern

Edited By choochoo_baloo on 30/05/2019 01:03:01

Hopper30/05/2019 00:46:36
3888 forum posts
83 photos

Get a quote if it does not cost the earth. Three phase is real handy to have, specially if you get into using welders and plasma cutters etc down the road. But makes it easy to use your three phase motors in the meantiine.

Paul Lousick30/05/2019 02:14:51
1255 forum posts
509 photos

3 Phase would be handy but check all costs . If 3 phase you may be charged for the use of 3 meters instead of one by electricity supplier. The 3 phase converters offer variable speed for your motors which you will not get with straight 3 phase supply.


Edited By Paul Lousick on 30/05/2019 02:15:32

Grotto30/05/2019 05:22:06
124 forum posts
71 photos

I looked at getting 3 phase into the house, but it was going to be minimum $12k (6,000 pounds) to get it to the switchboard.

Bought a rotary converter (4kw) for less than a sixth of the price which works great. I can also take the converter with me if I ever move.

If I’d got 3 phase in, I would have had to pay a monthly connection fee in addition to the one I pay for single phase.

There's a monopoly on power connections here in NZ so they can charge whatever they want.

John Haine30/05/2019 08:43:00
2779 forum posts
140 photos

Single phase and 3 VFDs, then you get variable speed too.

Nigel McBurney 130/05/2019 09:17:52
630 forum posts
3 photos

When I enquired about 20 years ago ,there was only two phase supply along the rd on poles (rural Area) though the pole outside our property also had the 11k volt cross country high tension supply so the quote included a updated transformer ,a used one which they had in stock 2 phase replaced by 3 phase..,about 100 yds of 3 phase supply cables to a meterd supply in the garage,

the electric used would be charged at full rate VAT unless I could demonstrate that the supply was domestic only.and they insisted that the supply went under ground from outside the brick built garage through the footings and up through the concrete floor.And I would have to do that work.quoted cost £3k and electrician friend said that I had to allow at least another £1k for distrubution electrics plus he said that put the lathe in the garage so that the electric co could see/inspect the installation and wire in the workshop down the yard after they hade gone,So for 20 years ago it was expensive. Yet another friend living on the fringe of a town about six miles away was a lot luckier ,the electric co were updating the supply down the lane to 3 phase and when he asked if he could have a 3 phase supply to his garage,there were no problems the cable just went through the garage wall,no mention of vat and lot lower cost,so make sure you get a quote,as my experience is the rules seem to vary.So I did not get the supply as it was too expensive and there was no guarrantee about which vat rate they would charge amd have managed with phase converters ever since,One a rotary is very noisy even when housed in an adjacent shed and the other is a static 6hpTRANSWAVE rescued from a skip,this is very quiet with no transformer hum and drives my 5 hp Colchester motor,but I never get a full five 5hp when heavy drilling the lathe starts to slow down with 11/4 drill at 500 rpm in ali. I may pay to investigate a larger inverter type system. I have one machine with a 1 1/2 motor inverter driven and this works well and is quiet.If you are spending a long time in your workshop a noisy rotary converter motor or transformer hum can be very annoying.

Robert Atkinson 230/05/2019 09:24:22
462 forum posts
21 photos

A proper three phase supply would be a positive advantage if you are at all likely to buy an electric or plug-in hybrid car in the future. It would allow the installation of a fast charger.
Additionally what is the rating and load on your existing single phase supply? Many only have a 60A feed which is 14kVA. This seems a lot but if you have electric heating / cooking / shower you might be running int the limits at peak demand.

Alternatively take a tap off a couple of neighbours of street lights for the other two phasesdevil
(just for clarity that;s a joke I don't advocate stealing electricity or making dangerous taps into wiring.)

Robert G8RPI.

not done it yet30/05/2019 09:54:17
3757 forum posts
15 photos

I suggest you take the “someone’s” advice and first find out how much a three phase supply is going to cost you...

Then come back here to those of us that don’t have a clue as to that cost, or make your own calculations on using the single phase supply for running the place.

Spurry30/05/2019 10:00:55
167 forum posts
59 photos

As others have said - It all depends on where you live. In our last house, a new 240v supply was required before completing the driveway. This was modified to a 3 phase supply for very little extra.

However when we moved to rural Norfolk with it's existing 63A single phase supply, the quote was £65,000 for 3 phase. This was out of the question, but they did condescend to up the fuse to 100A, when re-routing the 240v.

A rotary converter was circa £1000. This runs the mill alright, but I find the noise excessive, even when moved next door to the workshop.


Alistair Robertson 130/05/2019 10:24:17
68 forum posts
6 photos

A few years ago I built a new workshop behind the house, intending to take a supply from the domestic distribution box. Lo and behold the electricity company, Scottish Hydro were working in the street.

I got chatting to the guy in charge and asked if 3 phase would be possible. "No problem, we will run a cable in the duct to your house, under the floor and through the duct to your workshop. You will have to get an account for the supply and meter etc. but we could put it in tomorrow"

The next day after about an hours work I had a distribution box, meter and everything installed ready to have the supplier fuse installed. I filled in the form, sent it off and two days later I was up and running.

I cannot remember paying anything for the installation other than giving the guys some tea and some of my wife's hot oven scones freshly baked!

That could never happen today with all the rules and regulation in place but it brings back very pleasant memories of how things used to be!


Stuart Smith 530/05/2019 11:44:27
54 forum posts
10 photos

A similar question was asked on this thread:

some of the comments were incorrect, but you may want to have a read. Some comments were from forum members who have had three phase installed.

You can get a quote for 3 phase by contacting your electricity distribution network operator (DNO). The cost will depend on the location of the nearest suitable 3 phase main cable and the supply capacity you want . If you don't know who your DNO is, you can find out at this website:


Regarding your own internal wiring, a commercial/industrial electrician will be able to quote for the necessary work.


Edited By Stuart Smith 5 on 30/05/2019 11:50:23

Andrew Johnston30/05/2019 11:59:00
5067 forum posts
582 photos

I stand by what I wrote in the thread quoted above. The installation was expensive, but partly justified by updating an inadequate single phase supply.

I have recently had to change the single phase consumer unit that was installed as part of the 3-phase installation. The old one was plastic (as recommended by the regulations of the time) and replaced a metal one. The new one is metal again (as now recommended), as the plastic ones were found to have a tendency to catch fire in the event of a fault. So much for the ex-spurts.


Colin Heseltine30/05/2019 12:39:37
350 forum posts
87 photos

I put 3 phase in around 1986. IF I remember correctly it cost me around £600 for the connection. I did all the work. I dug from the 3-phase supply running up the road. It was about 6 ft down below the edge of my lawn where it bordered the path running up the road. I dug a 6ft x 6ft x 6ft to expose the cable all round. Dug 3-4ft down in the lawn and under the drive and dug under garage floor to the meter location. They supplied me with a piece of HD ducting which I laid and re buried. I fitted my own distribution board. The MEB (at the time) came and threaded cable through duct connected to my meter and into my DB. They then connected up to the main cable in the road. It was quite interesting to see them do this live without turning the power off.

I also did this at my parent house in the mid 70's for the lathes and mill we had in the workshop there.


Bazyle30/05/2019 13:02:31
4850 forum posts
194 photos

We had 3 phase run to the Men's shed last year, although at present we only have a single phase connection. It was about £5k including the about 100ft run of duct and cable from the housing estate through the hedge but the trench was extra done by our own subcontractor for about £1300. I will have to check the paperwork to see if there is any further breakdown. A very important part of the process was the man who watched the man who watched the trench while the third lad drove the digger actually digging the trench. This job creation programme is necessary to forestall someone jumping into the 2ft deep chasm and claiming thousands of pounds compensation.

Tim Stevens30/05/2019 18:17:28
1122 forum posts

There is a big advantage in the speed variation available with a Transwave or similar set-up. It can save a lot of time if you want a very slow drive - perhaps for winding a spring or a coil. And you need to think whether you do need all three devices powered up at the same time. And I see no reason why a device big enough to cope with your most powerful machine should not work OK with the smaller ones. If this sounds a possibility ask your potential supplier for advice regarding switching arrangements etc.

Hope this helps

cheers, Tim

SillyOldDuffer30/05/2019 19:09:37
4996 forum posts
1059 photos

I agree with Tim, and would point out 3-phase to 3-phase VFDs are often being fitted today rather than simply connecting 3-phase motors directly to an already available 3-phase supply. It's because the electronics provide better motor control. VFD's, one per machine. are a 'good thing',

The advantage of true 3-phase is there's no messing about with the wiring etc of machines designed to plug straight in to 3-phase. That's important if you have 3 machines to sort out!

The disadvantage of installing 3-phase is the cost which depends mostly on how physically convenient, or not, you happen to be relative to the distribution network. Only way to find out for sure is to ask for a quote.

When a domestic customer asks for a commercial quote it might help to mention a realistic budget to show you're serious. Many suppliers dislike engaging with innocents thinking £50 max for a job that might cost thousands.


john fletcher 130/05/2019 19:41:40
564 forum posts

I'm told by a couple of friends who have had 3 phase supplied, they said they were carrying out research and didn't have any problems or excessive costs or great discussion with the DNO. Both dug their own trenches and carried out their own installation work within their workshops. Much to my surprise, one used steel conduit through out and all metal clad switch gear. John.

not done it yet30/05/2019 19:50:59
3757 forum posts
15 photos

One can, of course, put in a large enough VFD to run all the main requirements at the same time (with switching on the VFD output side). Not sure if the really useful bits on a VFD can all be utilised, but if only one machine is operating, the variable speed could be.

Phil Whitley30/05/2019 20:52:00
997 forum posts
132 photos
Posted by Andrew Johnston on 30/05/2019 11:59:00:

I stand by what I wrote in the thread quoted above. The installation was expensive, but partly justified by updating an inadequate single phase supply.

I have recently had to change the single phase consumer unit that was installed as part of the 3-phase installation. The old one was plastic (as recommended by the regulations of the time) and replaced a metal one. The new one is metal again (as now recommended), as the plastic ones were found to have a tendency to catch fire in the event of a fault. So much for the ex-spurts.


The reason we have gone back to all metal clad CU's is that the ex-spurts did not realise that when an rcd or mcb fails, as all mechanical devices eventually do, they do not fail safe, and catch fire! A fuse always fails safe, but they are the EX-spurts, so they must know best. Pity the poor people who have just paid out a fortune to have their old wylex removed, and replaced by a brand new plastic CU. Good business for the fire brigades I suppose. Never known in 50 odd years experience for a consumer unit to catch fire with fuses in it, even when some idiot connects a 10kW shower to an old wylex, all they do is smoulder and give off a really offensive odout which leaves one in no doubt that something is wrong!

choochoo_baloo09/06/2019 18:53:31
206 forum posts
28 photos

As mentioned above, I've now had a 'ball park' figure from my Network Operator:

  • 30kVA capacity for my large 4 bed detached house + workshop + lots of headroom @ 3 phase.
  • My local sub station has plenty of spare capacity
  • Mains cable runs right outside my house under the footpath. In other words they stressed my house is in the ideal configuration for this work/minimal cost (no cutting up highways etc).

£3100 + VAT

so that's that! Included the above details in case it may help someone else gauge the likely cost for their own project one day.

I will go the converter route from Transwave after all. idea

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