Do I have 3 phase in my 1930s built house?

[ericmark]

You can get static inverters which are not fixed to one motor, however where there is an inverter per motor it also does the soft starting so you don't get lights dimming when you switch on, because of quantity made getting an inverter to work all the motors is often more expensive than one to power each motor, but step one is check how the motor is wired.

With small motors often they are 230 delta and 400 star but larger motors at 400 delta and 690 star so by starting in 690 volt setting it does not put on so much load then once running you swap it to 400 volt settings it is called star/delta starting. If the motor is 230 volt delta then the inverter does not need to step up the voltage, so they are cheaper than those which need to step up the voltage.

I think you will find three phase is expensive, OK inverters are not cheap but it is a one off cost.

 

[JohnW2]

It looks like if we got 3 phase it would cost a bit more in line rental, and there may be a cost for additional meter.

One might think so but, at least with my supplier (E.ON) there is no difference in tariffs (either 'standing change' or usage charges) between single-phase and 3-phase - in fact the tariffs (and even my bills) say nothing about the number of phases. My neighbours with single-phase supplies from the same supplier are offered identical tariffs, at the same prices, as I am offered (and paying) for my 3-phase supply. As for the meter, the suppliers surely supply and maintain, without specific charge, whatever meter is necessary to meter whatever supply one has.

One imagines that the cost of running a 3-phase supply to a building that does not already have one could be enormous. On the other hand, if the OP were very lucky in that the 'unused' phases already existed within the cutout, the cost of changing would presumably be minimal. However, such a request would inevitably bring about the question (already mentioned) of what loads were going to be connected to the 3-phase supply, so 'asking for the DNOs permission' would be almost implicit in asking for a 3-phase supply.

We frequently advise people that, even with a single-phase supply, they are required to seek permission from the DNO before using large loads (such as welders or equipment with big motors) on a 'domestic' supply, and I can but presume that at least some do seek such permission. What we never hear about is what the DNOs usually say when they are asked - does anyone know how common it is for them to decline to give permission?

Kind Regards, john

 

[Demon73]

Ive no intention of trying to take the cover of the cut out, thats a bridge to far for me. I did just measure the voltages, to neutral I get 240v, across the hot wires i get 424v, if that means anything I dont know. Will give the UK power networks a buzz monday and see what they say about max loads in my area etc, im also with EON so ill give them a buzz too, see what they have to say.
Cheers for the help so far, will let you know how it pans out.

 

[John D v2.0]

lucky in that the 'unused' phases already existed within the cutout, the cost of changing would presumably be minimal. However, such a request would inevitably bring about the question (already mentioned) of what loads were going to be connected to the 3-phase supply, so 'asking for the DNOs permission' would be almost implicit in asking for a 3-phase supply

You'd think so, but he could just ask the dno for a new cutout, which they may well so given the look of that one. Then if all 3 phases are there, they will terminate them all into a cutout.
After that the choice of meter is down to the meter operator, they are allowed to remove the seals and connect to the dno cutout to replace the meter.
I'm not saying it is or isn't, but sometimes departments in the same company don't talk to each other let alone different companies.

 

[ban-all-sheds]

to neutral I get 240v, across the hot wires i get 424v, if that means anything I dont know.

It means you do have at least 2 different phases there - phase-to-phase voltage is √3 x phase-to-neutral.

 

[JohnW2]

I did just measure the voltages, to neutral I get 240v, across the hot wires i get 424v, if that means anything I dont know.

Are you saying that you measured 434V between that unused fuse holder and your actual live supply? If so, that does seem to suggest that there are at least two of the three phases present. If the phase-to-neutral voltage is, as you say, 240V, then the phase-phase voltage should be about 416V (240V x 1.732, the latter being the square root of 3). So maybe there is some 'hope' for you!

Kind Regards, John

 

[John D v2.0]

If you're in there measuring things I hope your meter and leads are both marked CAT IV as anything less is not rated for live use in the he incoming supply.
Also if any terminals don't meet IP ratings for live test you should really be wearing special rubber gloves for the purpose.

 

[JohnW2]

You'd think so, but he could just ask the dno for a new cutout, which they may well so given the look of that one. Then if all 3 phases are there, they will terminate them all into a cutout. ... after that the choice of meter is down to the meter operator, they are allowed to remove the seals and connect to the dno cutout to replace the meter.

Interesting suggestion. I wonder, however, if the supplier/meter operator would be 'allowed' (per DNO rules) to put fuses into cutout fuse holders that the DNO had left empty?

Kind Regards, John

 

[John D v2.0]

Interesting suggestion. I wonder, however, if the supplier/meter operator would be 'allowed' (per DNO rules) to put fuses into cutout fuse holders that the DNO had left empty?

Kind Regards, John

Probably not, but ours came from the box with 100A fuses and the jointer replaced the one he used with a 80A and relabeled it

 

[JohnW2]

If you're in there measuring things I hope your meter and leads are both marked CAT IV as anything less is not rated for live use in the he incoming supply.

Theoretically true, but I don't think I've ever seen a multimeter that doesn't have a 600V AC voltage range, if not higher, so one imagines that the leads that come with it are regarded as being fairly safe, if used sensibly, to measure ~400V.

Kind Regards, John

 

[Demon73]

Are you saying that you measured 434V between that unused fuse holder and your actual live supply? If so, that does seem to suggest that there are at least two of the three phases present. If the phase-to-neutral voltage is, as you say, 240V, then the phase-phase voltage should be about 416V (240V x 1.732, the latter being the square root of 3). So maybe there is some 'hope' for you!

Kind Regards, John

Yep thats what I did.
I measured from the untapped live (left holder on the cut out) to neutral, that was 240v exactly.
From live to neutral, also 240v exactly.
From untapped live to live (ie across the two lives), that was 424v.

I had a quick read about 'split phase'. As I understand it they are set 180° apart so should have read something like 480v to be 'split phase'. 3 phase is set 120° apart i think, so measuring two legs id have thought would come out at something less than that, which it did, maybe theres hope .
Just had a look at the probes and they marked CAT III, i did wear some thick nitrile gloves, for no other reason than than i thought they cant hurt and thick wires scare the bungos out o me lol.

 

[JohnW2]

I had a quick read about 'split phase'. As I understand it they are set 180° apart so should have read something like 480v to be 'split phase'. 3 phase is set 120° apart i think, so measuring two legs id have thought would come out at something less than that, which it did, maybe theres hope .

That's all correct. It certainly sounds as if you have two phases of a 3-phase supply (not 'split phase'), which I would have though makes it pretty likely that the third phase also exists within the cutout (it's hard to see why just two phases of a 3-phase supply would enter a property) - so, as we've both said, there is definitely 'hope'!

You now need someone brave (and trained/experienced) enough, with appropriate protection, to open up that cutout and investigate - your DNO will have such people!

Kind Regards, John

 

[SimonH2]

which is 23 kW running at full load.

But apart from machine losses, the load will only be what he runs from the output.

Much higher currents when the motor is starting from stationary.

Indeed, some form of soft-start would be a good idea. In the past when I was experimenting with building a converter (with bits from dad's stock of motors and transformers), one of the starting methods I considered was a small "donkey motor" to spin up the main motor (being used as the rotary converter) before applying power.

 

[John D v2.0]

Theoretically true, but I don't think I've ever seen a multimeter that doesn't have a 600V AC voltage range, if not higher, so one imagines that the leads that come with it are regarded as being fairly safe, if used sensibly, to measure ~400V.

It's not just the voltage iit the let through energy of the upstream fault protection and the amount of exposed metal on the probes and the presence of finger guards.
You can get any old cheap imported meter that says 600v and I'm not sure the maker regards them safe according to our standards, but even if they're safe at that voltage on a high impedance supply that doesn't mean you can use them upstream of most of your protective devices at your cutout.

 

[JohnW2]

It's not just the voltage iit the let through energy of the upstream fault protection and the amount of exposed metal on the probes and the presence of finger guards.

The amount of exposed metal and the presence of finger guards are related to the safety of using the probes to measure a 'dangerous' voltage - if the meter is designed to measure voltages above ELV (and even a bit less that the upper limit of that), the supplied probles should be safe to use at such voltages, shouldn't they? I don't see what the probes can do about " let through energy of the upstream fault protection" unless they look like drainpipes - unless (per below) you're just talking about fusing!

... but even if they're safe at that voltage on a high impedance supply that doesn't mean you can use them upstream of most of your protective devices at your cutout.

What are you suggesting should be used in such circumstances? Are you perhaps talking about fused probes?

Kind Regards, John