Three phase wiring question.

[Spark123]

no but it might be a problem if it's driving the lift the wrong way and it's not seeing the limit switch ( wrong end )..

That would happen if the phase rotation to the motor was incorrect, doubt it would happen if the phase sequence to the control supply was different tho.

 

[mtkt29]

What we don't know is what it's supply was in the previous garage and what I wonder is if in previous garage it was supplied through an inverter and had three phase 230 volt not three phase 400 volt. You of course can check all you want and would be unlikely to find it. If it was 230 volt feed then all motors will have been changed from star to delta and the transformer would be connected phase to phase instead of phase to neutral.

Thanks for your reply, the ramp is brand new. The guys put in the ramp but would not touch the electrics. They told the electrician 1) it needs a neutral and 2) it needs to be earthed. So the fact it needs a neutral and has a neutral terminal in the control panel, am i correct in saying it should be three phases and neutral all connected at 230v between N and phase and 400v between all phases? and that if it needed 400v then it would not require a neutral?

Have they removed covers from motors?

The guys didnt hang around or remove any covers just said the transformer must be 'dodgy' and we will bring a replacement!

 

[rebuke]

3-phase motors themselves don't need a neutral, i.e. they work on the 400V between phases, with the phase rotation determining which direction it will go.

I suspect the neutral is for the control circuitry, which probably runs at 230V or lower, so just uses one phase etc...

 

[ericmark]

Although many three phase supplies don't require a neutral the reverse is also true many do require a neutral.
So if they ask for three phase and neutral that's what they need.
I had miss read and if brand new forget all I said about inverters it will not apply.
All electrical equipment should have a plate giving the electrical requirements.
And if the guy thinks the transformer is faulty why do you ask your questions do you not believe what he said?
I have a phase rotation meter but many electricians don't and it has caused as many problems as it has solved where I have fitted a socket correctly but then found all other sockets in factory are wrong way around so most electricians use the motors them selves as phase rotation meters.
It would be normal to have three sets of workers to install a new piece of equipment. Electrician puts in supply, Fitters install ramp, installation / commissioning engineer checks all the work and sets up any items needing adjustment.
It is up to the installation / commissioning engineer to spot any problems and if minor correct. This would be guy who said transformer is faulty as until handed over for you to fiddle could cause problems.
Under normal circumstances one just stands back and let them get on with it.

 

[mtkt29]

I suspect the neutral is for the control circuitry, which probably runs at 230V or lower, so just uses one phase etc...

Thanks, i see what you are saying. But am i right in saying that all three phase wires would have to be connected to the three phase terminals in order for the motor to work? And that the neutral would just use one phase for the control circuitry?

 

[rebuke]

Phase rotation can be very confusing - I work backstage in a theatre at times, which obviously has quite a beefy 3-phase supply. It turns out that the whole area has a phase reverse (e.g. what is normally L1,L2,L3 is L1,L3,L2 or similar), but some clever person fixed it at the incomer (red->red,yellow->blue,blue->yellow or whatever). This is quite useful, as we occasionally hire in 3-phase kit, and it's just useful to not have to rewire plugs etc!

However, whenever we get a local spark in who knows the area to work on something 3-phase (e.g. electric winches, big power tools such as pillar drills, compressors etc), they get very confused as they compensate for the phase reversal at the output, only to find it's already right and they've just made it wrong!

 

[rebuke]

The neutral won't 'use' a phase at all, it's a return path - so anything that isn't using all 3 phases (i.e. isn't balanced across them), will return current down the neutral. Assuming there is control circuitry, that will almost certainly be 230V (or even lower), so will need a neutral.

It is possbile the motor requires a neutral, as has been said, some do, some don't, it just depends how it's built...

 

[mtkt29]

And if the guy thinks the transformer is faulty why do you ask your questions do you not believe what he said?

Thanks eric, i do believe what was said, its just that they did not check the wiring prior to turning on the machine or after the transformer blew. Just said 'dodgy' transformer and went. What i was trying to find out was that if they came next week and just replaced the transformer and wired it up as before it may go bang again!
But you are right, i will let them sort it. Thanks for your help

 

[rebuke]

While it's their problem, if it goes bang again when they fit the replacement - I would suggest trying to gently persuade them to verify they have connected to the correct terminals, if they had swapped one of the phase conductors and the neutral, then that could end up putting 400V across a transformer that's designed for 230V, which could easily make it go bang...

 

[ericmark]

Thanks, i see what you are saying. But am i right in saying that all three phase wires would have to be connected to the three phase terminals in order for the motor to work? And that the neutral would just use one phase for the control circuitry?

Yes if not the motor unless protected would burn out. Normally they are protected.

And yes neutral will just be for control. Where a transformer is fitted for control on a three phase unit normally the supply to transformer would be 400 volt but I will guess the basic same unit is used with both single and three phase customers so they use a standard control panel for both. Hence why you have a neutral connected.

 

[Spark123]

It is slightly odd you are referring to the old colours i.e. Red, Yellow and Blue for the phases, Black for the neutral but you say it is a new install, hence Brown, Black and Grey for the phases, Blue for the neutral. They haven't got the black n blue mixed up by any chance have they

 

[conny]

When was this wired up? If recently the cables should be brown/grey/black for the phases and blue for the neutral.

Already suggested that one but got no reply.

Eric,

are the links connecting three terminals together or three sets of two terminals together the latter is the higher voltage.

sorry but you have it wrong. When connected in delta, (3 sets of 2), then that is the lower voltage setting. i.e.230v.
Connected as 1 set of 3 and 3 individuals is star connected and for 380/440v use.

 

[ericmark]

Thank you conny I will correct now.

 

[ColJack]

you sure about that conney?

when connected in star, the voltage across each winding of the motor is 230V ( phase to star point. ), when connected delta, it's 400V ( phase to phase )....

the motors are marked counter intuitively..

the ones we use at work are marked 400 delta, 660 star.. ( or whatever the new equivalents are.. )
this indicates that to produce the same running torque, a phase to phase voltage of 660 volts is needed when wired in star, as opposed to a phase to phase of 400 volts when wired in delta

EDIT: which is exactly what you said above... sorry, my drink addled brain is having trouble with words tonight..

so yes, a motor marked 230/400, D/Y should indeed be connected as delta from an inverter ( or transformer ) fed supply of 230v PHASE TO PHASE...
but if connected to a standard 400V 3 phase supply then they should be connected as STAR...

 

[ericmark]

Glad I was not only one. Lost a few motors where inverters went down and electrician did temp connection to three phase and forgot to change links.