# Three Phase or Single Phase?



## Woody2Shoes (29 Jun 2018)

I am fortunate to have a new workshop on the drawing board.

I am an amateur woodworker, but hanker for a big boy's bandsaw and spindle-moulder.

Given the state of the existing domestic electricity supply, I'm fairly sure I will need a separate - new - supply for the workshop.

The question I have is the relative costs - of installation and of ownership - of three phase vs. single phase supplies for an essentially domestic customer. Before I speak to my DNO, and probably lose the will to live, I thought I'd ask you lot for your thoughts.

Thanks in advance W2S


----------



## Ttrees (29 Jun 2018)

Are you OK with the additional tariffs?
The cost of installation could be huge, depending how far you're away from the 3 phase transformer.
I checked my 3hp 24" bandsaw on VFD draw recently with no load running a 1" tuffsaws blade and went out to check the meter...it was drawing little more than my ageing laptop.
This might not be so little if I started cutting though...although in use, cutting a quarter of its capacity
it dosen't skip a beat,
Another examples with my old Startrite 12" tablesaw with VFD, cutting at near full capacity seems to be no bother on my supply, although starting a 1hp drill will dim the lights
Dont know how much juice a spindle moulder will need however....
Might be a problem presuming you want to have a decent sized dust extractor running also
Tom


----------



## Woody2Shoes (30 Jun 2018)

I was hoping someone could tell me, an example of the difference in tariffs. I can't seem to see any distinction made on the DNO's website.

There is a three-phase LV cable in the road, aside from the cost of a few metres of different cable (and a different meter) the installation cost would be pretty much the same (horrendous) - but because the existing domestic supply is inadequate, I'm going to have to bite the bullet and pay for a "new supply". My only question is if I went for 3-phase, what am I likely to spend in addition?

Cheers, W2S


----------



## mbartlett99 (30 Jun 2018)

Initially your set up will be more expensive as, apart from anything else, your outlets/switchgear and cable will be of a much higher standard than normal domestic rubbish. If you're a reasonable electrician its not difficult to install outlets etc but of course it will need to be signed off by a sparky.

The savings will come when buying large equipment; 2nd hand you'll now have a full choice across the board. Also you won't need to sweat about buying something the supply can't handle. Even a good single phase supply is going to tie you to 3kw or less which when you mention spindle moulders is towards the lower end. You can get pretty large bandsaws on 16A so that might not be deciding factor.

3 phase motors are more efficient, physically smaller and smoother in operation but as a hobbyist that will probably not be a siginificant factor.


----------



## deema (30 Jun 2018)

For the level of electricity usage you will have for a home shop you will be on a standard domestic tarif. Just like for your home you can shop around to find the best deal for the amount of electricity you use. It’s only if you really start to use a lot of electricity does the tarif really start to change. I have a 100A / phase feed and being a one man band don’t use enough for anything other than standard tariffs.

For installation 3ph will always be more expensive, however to keep costs down keep you demand requirement as low as possible. The biggest cost is the proportion of the transformer cost the allocate to you. The smaller the load allocation the cheaper it is. On your own land you can dig your own trenches and lay the conduit which they supply to keep costs down.

Mains isolators, same price whether 3ph or 1ph. 3 ph may be cheaper as you will need a lower current rating

Wiring, 3ph will generally be cheaper, the current / load per phase is lower and won’t require the same thickness of cable. 

Distribution unit (consumer unit) about the same price for the same number of take offs. You can mix single phase and 3ph take offs from a distribution unit, MCbs for single phase are the same and 3ph a little more expensive

Plugs and sockets - no real price difference between single and 3ph cost. The 3ph plugs and sockets will all probably be 16A as opposed to 32A for some of the equivalent single phase.

Machine and kit is where savings can really be made, 3ph machines are plentiful and go for buttons compared to 1ph. Depending on what and how many machines are on your shopping the difference in secondhand prices can easily offset the additional cost of the 3ph supply. 

Value of your property, well anyone who likes a workshop, woodwork, metalwork, plays with cars /motor bikes etc is going to love the fact that you have 3ph. So although not adding value it will make it more appealing for a buyer with an interest in a workshop.


----------



## custard (30 Jun 2018)

As electric vehicles and home charging becomes more common, will this increase the attractiveness of a domestic 3 phase supply?


----------



## Woody2Shoes (30 Jun 2018)

custard":30hyr7d2 said:


> As electric vehicles and home charging becomes more common, will this increase the attractiveness of a domestic 3 phase supply?



That's another factor in my thinking. I'm pretty sure that I can charge a car fast enough, for my needs, and based on current (no pun intended) technology, on a single phase supply (but again, it would have to be separate from the existing domestic connection).


----------



## Sideways (30 Jun 2018)

custard":3j1hgiom said:


> As electric vehicles and home charging becomes more common, will this increase the attractiveness of a domestic 3 phase supply?



Sort of depends I think.
The common, cheap EV charge points sold today for domestic use are "type 2" and basically they just deliver a 16 or 32 amp 240v single phase supply to the car with an RCD and a little electronics in the loop.
They rely on a charger unit in / with the car to turn that mains supply into DC and charge the batteries.

To take advantage of having a 3 phase supply you would need a charger designed to be fed from 3 phase. I'm going to guess that these will be more expensive as most domestic and small commercial customers won't have 3 phase so there will be fewer sales to drive the price down.
BUT
You have install a fixed EV charge point on it's own dedicated circuit so if you put that on one phase and spread the rest of your single phase circuits around the other two phases, you could balance the load a bit.
Vehicle charging's going to have quite a hit on the supply network. As it takes off folk will be connecting 32A loads for hours at a time. The power companies actually only allow for an average demand of 8-10 Amps per household when they size their supplies in residential neighborhoods. A 300% increase is going to be a challenge


----------



## Woody2Shoes (1 Jul 2018)

Sideways":2potpfvj said:


> ...
> BUT
> You have install a fixed EV charge point on it's own dedicated circuit so if you put that on one phase and spread the rest of your single phase circuits around the other two phases, you could balance the load a bit.
> Vehicle charging's going to have quite a hit on the supply network. As it takes off folk will be connecting 32A loads for hours at a time. The power companies actually only allow for an average demand of 8-10 Amps per household when they size their supplies in residential neighborhoods. A 300% increase is going to be a challenge



My neighbour has 4kWp of solar panels - maybe I should only charge a car on sunny days (and from the same phase as him!)?!

I think the "dedicated circuit" bit is the key thing for me - I know I'm going to need a new supply for the workshop, I think it could quite possibly feed one of these as well:

https://chargemasterplc.com/products/


----------



## HOJ (1 Jul 2018)

I would get onto the DNO in the first instance, before getting too involved in the merits of 3 phase, I had a quote of £3000.00 + VAT to drop a supply off an overhead, down a pole, in my garden, to a box on the ground, then they told me they needed a bigger transformer, that was another £8000.00...

I am working on a project to build Glamping pods, in a field, quote for Electric so far is £12000.00 + VAT.


----------



## Sideways (1 Jul 2018)

mmm
I wonder how many solar panels, big NiFe cells to store the energy (claimed to last 20+ years, way better than lithiums) and LED lights you could buy for that ?

It's a mighty wedge of cash !


----------



## loftyhermes (2 Jul 2018)

Have you thought about buying a 3ph generator?


----------



## custard (2 Jul 2018)

It would be great if someone wrote the definitive guide to Three Phase Converters and it was posted as a sticky.

This gets raised often, but it always runs into the classic problem of internet forums. There are some people who really know what they're talking about and others who don't, but in the cacophony of a forum it's difficult to tell one from the other. At least in a sticky thread someone has taken a lead, their qualifications get "peer group reviewed", and so you can feel reasonably confident in the advice.


----------



## deema (2 Jul 2018)

There is a really good overview that’s been written already and been linked to in other threads. However, it does contain errors, one of which could be serious, so if you find it don’t take it verbatim.

The problem with trying to produce an ‘idiots guide to 3ph from 1ph’ is that like most things, although is very easy to do, you need to have a lot of background knowledge to do it safely. In most cases people get away with it, but not always. 

Take for instance the humble DOL (Direct On Line starter). Feed the power into one side and take the output to your motor. What can go wrong? Well, a lot actually. I bought a machine recently with the DOL wired just like that......what they had failed to recognise is that the energising coil for the contractor must be fed through the overload relay normally closed contacts. The overload relay was set to self reset (most are) so after it had cooled down after an overload it would make contact again. The consequence of this simple error is that if (as it was) it was wired to say a circular saw and it cut out due an overload, the saw would stop.....but after a few minutes the saw would restart and run again all by itself. 

It’s great to have information in order to make an informed decision on which route to take, but unless you really know what your doing, I can’t emphasis enough get a proper industrial electrician (not someone who makes a living wiring houses) to check out what you’ve done / do it for you. They aren’t that expensive and it beats not being able to count to ten or worse.


----------



## RickG (3 Jul 2018)

In a previous life I was an Electrical Building Services Engineer. I'm a few years out of touch with certain aspects, but the principles haven't changed.

If you have a normal domestic supply you will have a 230v 100A supply. This comes in using 3 cables: Brown Bue & Green Yellow (to state the relatively obvious)

A 3ph supply will come in using 5 wires: Brown, Black Grey; being the Live supplies. Blue is the Neutral and Green/Yellow is earth.

If you have a 3-phase supply you need to balance your electrical load across all 3 phases. Although, generally, my guess is other than the 3ph motors, you won't have a lot of load that can be shared equally.
The danger of a 3ph supply is, where in a domestic situation, there is a risk of a 230v shock; with 3ph this is 415v. So this brings a lot more of a demand on safety precautions. In certain situations you may need to label outlets as to what phase they're on.

In relation to getting a 3ph supply to a domestic property, this is physically possible as it's effectively getting 2 new supplies. Yours and the rest of the houses on your road will be balanced over the 3 phases, by houses each being on a different phase of a 3ph supply. 

The big question is "will UK Power Networks let you have a 3ph supply in a domestic property?"
Bear in mind here that you could sell the house and the next owner won't have a clue what you've left them with. UKPN won't be told to take it out and danger will be lurking.

If I was the engineer making this choice. There is no way on this earth that I'd allow you to have a 3ph supply in a domestic house. But I'm not making the choice.


----------



## Woody2Shoes (3 Jul 2018)

RickG":eepb3mqu said:


> If you have a 3-phase supply you need to balance your electrical load across all 3 phases. Although, generally, my guess is other than the 3ph motors, you won't have a lot of load that can be shared equally.
> The danger of a 3ph supply is, where in a domestic situation, there is a risk of a 230v shock; with 3ph this is 415v. So this brings a lot more of a demand on safety precautions. In certain situations you may need to label outlets as to what phase they're on.
> 
> In relation to getting a 3ph supply to a domestic property, this is physically possible as it's effectively getting 2 new supplies. Yours and the rest of the houses on your road will be balanced over the 3 phases, by houses each being on a different phase of a 3ph supply.
> ...



My neighbour has a 3-phase supply in his agricultural barn. I'm not proposing to have all three phases in my house - just my new outbuilding.

The system surely has to allow for a certain amount of imbalance in loads across the three phases - there are about eight dwellings (ignoring the barn, and the property with solar panels) sharing the nearest transformer. How does three-phase metering work at the premises (must all three phases draw identical current)?

I take your point about safety - personally I find 230V (or 253V as it is here at the moment!) sufficiently terrifying!


----------



## n0legs (3 Jul 2018)

RickG":28o7sgdt said:


> If you have a normal domestic supply you will have a 230v 100A supply. This comes in using 3 cables: Brown Bue & Green Yellow
> 
> The danger of a 3ph supply is, where in a domestic situation, there is a risk of a 230v shock; with 3ph this is 415v.
> 
> If I was the engineer making this choice. There is no way on this earth that I'd allow you to have a 3ph supply in a domestic house. But I'm not making the choice.




Not many domestic properties in my experience have a 100A supply, but I'm prepared to be proven wrong.
Most domestic supplies are 60A or 80A.
The phases colours could still be Red and Black.

The risk and danger of a 3 phase supply in a domestic property is negligible. If it has been installed correctly and maintained correctly it will be and remain safe. Commercial and industrial premises are the places where 3 phase gets abused, normally by people/maintenance staff out of their depth.

In my experience if the customer can prove the need for a domestic 3 phase supply they can usually get it, provided they can afford it.

WTS, get hold of the DNO for your area and get a quote. Don't forget you don't need to use the DNO for the connection. There are approved contractors available, ask the DNO for their list.

I haven't had anything to do with LV in a long while, EHV is my game these days. The DNO's don't bite, they're always happy to advise.
All the best
n0legs, 30+ years a DNO Engineer.


----------



## Sideways (4 Jul 2018)

RickG":2fftvbp4 said:


> The big question is "will UK Power Networks let you have a 3ph supply in a domestic property?"
> Bear in mind here that you could sell the house and the next owner won't have a clue what you've left them with. UKPN won't be told to take it out and danger will be lurking.
> 
> If I was the engineer making this choice. There is no way on this earth that I'd allow you to have a 3ph supply in a domestic house. But I'm not making the choice.



Interesting perspective. I'm going to be denied a service because of some hypothetical risk to a 3rd party some 20 years in the future when I'm dead and gone ? Bit nanny state and not very customer oriented. Awkward too since of course there isn't any real competition when there's only one Distribution Network Operator in any part of the country. 

I come from the other direction. OFGEM on behalf of the UK govnment and the EC are enforcing universal service obligations for the supply of essential energy services to UK citizens and businesses. OFCOM are doing the same thing trying to ensure that we can all get broadnband. 
I'm asking for a "standard" product. It's my business what I want the power for and my business to ensure that it's use on my premises is done safely.
The DNO's job is to deliver the service to me in a safe manner within standard deadlines.
It is reasonable that they can verify that there are standards compliant cable, fuse and main isolator switch in my property if they didn't install them, there it stops.
I'd be very annoyed and taking it further if I asked for a 3 phase service and the DNO said no for any reason other than a short term practical inability to deliver it.

All irrelevant to me personally as I have a 60 amp single phase supply which is plenty and wouldn't want to spend the money to get 3 phase. I'm just arguing for those with more space and toys than myself to have the freedom of choice


----------

