3 phase output

[fattwat]

G'day, can anyone tell me what voltage I should get at a 3 phase socket and how to test it? there are three wires plus earth and across two sets of two wires I get 240 v across th eother set I get 400v. and I don't think that is right. thanks

 

[RedHerring2]

I don't think it's far away. It used to be 415v across phases in the UK. I don't know if it still is, or indeed what it should be in France.

Having said that, there should be three phases, From any one to earth/neutral you should get about 240v. Between any two of the three phases you should get about 415v.

 

[fattwat]

Having said that, there should be three phases, From any one to earth/neutral you should get about 240v. Between any two of the three phases you should get about 415v.

thats not good, I only 240v between the phases except for between blue and brown which is 400v. I'll check between each phase and earth and see what that throws up. of course it might be hat the wire are messed up and what I think is earth (green/yellow) is actually a phase. oh! deep joy

 

[Paul_C]

I think that officially France is supposed to be 230/400V now, just the same as "officially" the U.K. is 230/400V. In practice though, the nominal French voltages were 220/380V for a good many years before all the EU standardization business, so if they played the same "just mess around with the permissible tolerances" trick as we did here in order to refer to our existing 240/415 systems as 230/400, then you should still expect to see voltages which are nominally 220/380V, at least in some places.

But there are the usual variations from the nominal declared voltage anyway, so as long as you read somewhere in the 230-ish range between each phase and neutral, and somewhere in the 400-ish range between phases, it's correct.

If the socket is just 3-pole plus earth though, it might have been intended for a delta connection without neutral. What type of socket is it? Is it a IEC309 type, or one of the specifically French receptacles?

 

[RedHerring2]

I've got a three phase supply also, well I assume that I have. I haven't checked the voltages and I'm only using phase 1 & 2 at the moment.
Phase 1 will feed the house when it's finished, phase 2 is feeding the garage & caravan. So I know those two phases are OK to neutral.
I haven't used or checked phase 3 yet, other than to check it is live. I just assumed it's OK.

I haven't checked the voltages between phases either, I thought no need I have no intention of using any 3 phase equipment.

I will use phase 3 in the future for the other part of the renovation. Thus avoiding any possibility of 3 phases within the same building.
Edit:
Sorry about that, I was talking out of my arris!

I've just checked (it was three years ago that I sorted it out)

I've got a 4 wire supply, a greeny-blue, a brown and two blacks. there's no earth supplied. it's a local rod in the ground.

All of my current supply is between the brown and greeny-blue. That's where the supply was taken from, for just a few lights when I took over the place.
I'm pretty sure that the two blacks are also live, 'cos I've just taped them up for now in the distribution board, with the intention of using then in the future.

 

[Paul_C]

I've got a 4 wire supply, a greeny-blue, a brown and two blacks.

That's common in many Continental European countries: Blue for neutral, plus various permutations of brown & black for the phases (typically one brown & two blacks, but sometimes two brown & one black, all brown etc.).

In France, single phase cables within the home are often red & blue instead of brown & blue. And with older wiring (typically pre-1970's) you'll find completely different schemes employed.

 

[fattwat]

I've got a 4 wire supply, a greeny-blue, a brown and two blacks.

That's common in many Continental European countries: Blue for neutral, plus various permutations of brown & black for the phases (typically one brown & two blacks, but sometimes two brown & one black, all brown etc.).

.

Thanks for that, it would appear that is what I have and someone has wired the socket up wrong. Now for the interesting bit.;.. I have a piece of equipment that uses a 3 phase motor, the motor is wired up in the star configuration ( i think thats how its called! six terminals, three on one side of the block connected together and the other three going to the phases) with a seperate earth terminal. what wires do I need to use from the socket? do I use the 3 phases,( 2 blacks and a brown) and the neutral with a seperate earth?

thanks again jmm

 

[RedHerring2]

I'm no qualified electrician, and I suggest you check it out with someone who is. Try the other electric forum if there's no response here.
I would have thought that the difference in French and UK star/delta configurations will be negligible.

I believe you only use the three phases and earth. It should be a balanced load, therfore there is no need for the neutral.

In three phase the neutral only carries the residual of the unbalanced load.

I can't remember if the three phases are equidistant apart at 120° and you can use any phase in any order, or whether the phases need to be in a strict 1, 2, 3 order. In which case you will need to identify the R, Y ,B or 1, 2, 3 phases.

 

[Paul_C]

I have a piece of equipment that uses a 3 phase motor, the motor is wired up in the star configuration ( i think thats how its called! six terminals, three on one side of the block connected together and the other three going to the phases)

It certainly sounds as though it was wired in star, a.k.a. wye configuration. As RH2 has said, the neutral in a 3-phase system carries only any imbalance current between the phases, so with a balanced load such as this, it's possible to omit the neutral (if used, it would be connected to the common point of the three windings).

If there's a specification plate on the motor which gives details, perhaps you could take a picture and post it for confirmation.

what wires do I need to use from the socket? do I use the 3 phases,( 2 blacks and a brown) and the neutral with a seperate earth?

I think you need to double check what you actually have at the socket. Again, what type of socket is it? If there are four connections, then there's a good chance that it is providing three phases and earth, but no neutral connection. You indicated that you have a green/yellow earlier, which should be earth. You also indicated that you were reading 400V between brown and blue, which suggests that somebody has used blue as a phase rather than as a neutral.

If the socket is providing just three phases plus earth, then you should see somewhere in the region of 380 - 440V between any two phases (try all three permutations: A-B, A-C, B-C) and about 220 - 250V between each phase and earth.

I can't remember if the three phases are equidistant apart at 120° and you can use any phase in any order, or whether the phases need to be in a strict 1, 2, 3 order. In which case you will need to identify the R, Y ,B or 1, 2, 3 phases.

The phase displacement between each of the three phases relative to neutral is indeed 120 degrees, and that's what creates the rotating magnetic field which determines which way the motor will turn. If it turns the wrong way, the direction of rotation can be reversed by swapping any two of the three phase connections.