Run a 3 phase lathe coolant pump on single phase.

[normspanners]

the problem you have if the neutral becomes disconnected or has bad connection,and one item is still plugged in and one is unplugged but left switched on the connectors of the separate unplugged plug will now become live will they not.

I meant to say if the neutral lead on the 3ph socket is damaged or loose the neutral connectors of the seperate unplugged socket (not plug obviously) would then become live -----sorry.
forming a 'borrowed neutral' ?

 

[normspanners]

We do a lot of 3 phase heating stuff in work - not many actually have a neutral, though there's all sorts of different configurations you can get.

Those separate three phase heaters connected with no neutral must be switched all together at once though surely ? and will have an imaginary 'neutral' star point.

 

[normspanners]

you would need a neutral though one of the problems of doing that is you can overload the neutral in the run from the CU to socket

Some three-phase four-core cables have a neutral of reduced cross-section on the assumption that there will be some degree of balance. Such a cable must not he used unless the installer is certain that severe out-of-balance conditions will never occur. Similar action must be taken with a three-phase circuit wired in single-core cables. A reduced neutral conductor may only be used where out-of-balance currents will be very small compared to the line currents.

this was my concern although I might not have explained myself correctly, but as we dont know the wiring config especial as Ed.was saying he has several single phase outlets from a 3 phase socket it was a possibility that could cause issues.

 

[daleyd]

Those separate three phase heaters connected with no neutral must be switched all together at once though surely ? and will have an imaginary 'neutral' star point.

What do you mean "switched all together" - they will be fed from one source (supply) and they will typically be switched by thyristors (which is the part we supply, obviously you can get ones that aren't but they would just be fed by a contactor and be on/off control) - sometimes they will have thyristors on 2 legs out of the 3, sometimes thyristors on all 3. The return path is always through one of the other legs - I have some notes/background theory on it somewhere I'll post it up when I find it.

 

[normspanners]

They all must be switched together though, if 230 v, as a 'bank of heaters' not each switched separately. If 415 v they could be separately controlled.

 

[daleyd]

They all must be switched together though, as a 'bank of heaters' not each switched separately.

Yes, it's 1 heater supplied by three phase - otherwise it would be 3 single phase heaters?

 

[normspanners]

otherwise it would be 3 single phase heaters?

I thought thats what we where talkin about,

so if you have a 2kw heater attached to each phase, it;'s just the same as having one 6lw 3phase heater - negative isn't even needed

I'm gettin Mucking Fuddled here. especially as we are getting into the realms of--- DC now

 

[Pete.]

 

[normspanners]

I think this is a bit fftopic: Pete

BTW Is the service after and towards the thread direction or is it before and towards the original post because I need to visit services and pick up brain cells before reaching the conclusion of the original post

 

[daleyd]

Seeing as the thread was originally about a 3 phase motor im not sure how it got here either

 

[Ed.]

this was my concern although I might not have explained myself correctly, but as we dont know the wiring config especial as Ed.was saying he has several single phase outlets from a 3 phase socket it was a possibility that could cause issues.

My 3 phase wall sockets are 5 pin (3A+1N+1E) each connected to a 3 Phase circuit breaker and an RCB in the shed sub-box, and there is only 1 x 240V 15A GPO connected to each of the 3 phase wall sockets in the shed. The 3 phase wires going in to the main circuit box on the house are each separated to a circuit in the house, ie: 1 going to GPO's. 1 going to the water heater and the last to lights and aircon, and so forth to attempt some sort of load balancing. There are actually more circuits involved but this is just an example, my property actually has 5 sub-boards on it plus the main circuit box.The 3 phase is the equivalent of three separate out of sync 240V lines, unless they are combined to run in 3 phase in which case it becomes about 415V.

As to the cables, all of the 3 phase cables here have the earth cable a size smaller than the other cables, so a 3 phase 16mm cable will have a 10mm earth and all the others (3A & 1N) are 16mm.

So running a or single or even more 240V GPO's (1A,1N & 1E) off a 5 pin 3 phase socket is the equivalent of a house with just single phase going in to it, also assuming that the wiring size is adequate, which in my case is overkill. On the street each house with 240V only gets connected to an alternate phase so they try to load balance the load to the street transformer. Hope this explains my wiring a bit better.

 

[Ed.]

Seeing as the thread was originally about a 3 phase motor im not sure how it got here either

I think I derailed it by asking about the capacitor?

 

[normspanners]

Well if it works it works you dont need capacitors coz you have 3 phase maker doesnt and needs them end of, thank you and good night, hope we all live a long and prosperous life and dont get electrocuted though I think I could do with a quick shot before bed just to keep the seizures at bay------- bbbzzzzzzzzzzzzzzzz ah thats better. nigh nite