Three phase wiring question.

[mtkt29]

Hi, hope someone can help, we have had an electronic pump operated ramp put in a commercial garage. The supply is 3 phase and operates through an isolator. When the electrician installed the ramp we got power but within about 1 minute there was a bang and the transformer in the control panel had blow up!
The people who put the ramp in said that it was an electric error, but the electrician assures us it is perfectly fine. If i explain the set up could anyone give there expertise / views.

Machine needs three phase and neutral.

Firstly, a Hager three pole C32 breaker - coming out of that from top to bottom - red, yellow then blue and the black into the neutral terminal.

Secondly, this cable goes into an isolator (handle) type. The 3 phases into three terminals and the neutral into one off to the left.

Thirdly, a new cable from the bottom of the isolator (in the same terminals as the supply) going into the terminals in the control panel of the new machine.
These cables go red into L1, yellow L3, blue L5 and the neutral in N terminal. (Would this matter what terminals each phase goes into?).

Does this setup sound okay? Whent the transformer blew the breaker did not trip. My feelings are that the setup looks good and would take longer to blow the transformer if there was a wiring issue / or they would be no power at all???

Thanks if anyone can help.

 

[conny]

Thirdly, a new cable from the bottom of the isolator (in the same terminals as the supply) going into the terminals in the control panel of the new machine.

Do you mean that all the cables are in the same side or are 3 in one side and 3 in the other side? If they are all in the same side then they are not going through the isolator.
When was this wired up? If recently the cables should be brown/grey/black for the phases and blue for the neutral.
A straight forward wiring short would blow immediately whereas a fault on the tranny may take a bit longer to occur. i.e. it would take high amps and get hot before blowing. Should have tripped the breaker though whatever the problem.

 

[Spark123]

It would matter which way around you got the phases in the respect of your 3 phase motor will run backwards if it doesn't have the correct phase rotation.
Main thing here is the neutral is connected to the correct place, each phase to neutral is 230v. Phase to phase is 400v - (hate the new figures)
As far as causing the transformer to burn out - what voltage is the transformer coil? How is it connected?
Sometimes a smaller control fuse is included inside the panel for the control side of things. Somethimes it isn't fitted, the C32 probably won't clear with a faulty transformer or one which is being fed over voltage. Doubt a control fuse would clear them either before the coil was permanently damaged.

 

[ericmark]

You do not say why the transformer went bang. Most likely is that a phase and neutral has been swapped and 400 volt was feed into something designed for 230 volt. The manufacturers are not daft and know if that is the case most electricians with look for fault and correct well before they arrive on site. With this in mind it is normal for manufacturers to commission items and check for mistakes before it is switched on.
If the job has been done correctly the electrician before switching on should complete an installation certificate. In doing this he should find any faults when he is taking the readings for the schedule of test results and if this has been all filled in and presented then likely the electrician did everything A1.
But it is no proof and if the transformer has blown then it would point to a mistake on electricians part.
Having said that we had a transformer go bang. On the AVR of Connah's Quay Power station and on investigation the AVR had three fans which were 3KVA each and were powered by a 11kv to 400v 6KVA transformer seems the French who made the AVR could not do simple maths 3 x 3 = 9 not 6 so some times manufactures can make mistakes! Yes it was a big bang!

 

[Spark123]

Seems a bit of a puny supply to go to the trouble of transforming 11kv down for!
Most electric showers consume more than that.

 

[ericmark]

It was the only supply available in the area direct from the 11kV alternator.
If sensing voltage one really does need to connect to output from alternator not through some round about method.
I was only the electrician who had to move things to make room for bigger transformer and connect it up I did not design it. I can add up so could not have been my job? That was done by some French "Engineer" at least he said he was?

It seemed to upset him when we chanted 3 x 3 are 9! He really did get some stick.

 

[mtkt29]

"Do you mean that all the cables are in the same side or are 3 in one side and 3 in the other side? If they are all in the same side then they are not going through the isolator."

Sorry, yes 3 in the top and 3 out of the bottom. My only concern with the isolator is where the neutral should go. There is a seperate terminal to the left of the phase terminals which it is in. However with the ramp that was taken out it seemed that this black wire (neutral) in the consumer unit was used as an earth (in the earth terminals)? But there is a seperate earth terminal in the isolator.

 

[mtkt29]

"It would matter which way around you got the phases in the respect of your 3 phase motor will run backwards if it doesn't have the correct phase rotation".

Thanks for your reply. I know it is probably simple but how would i know if the phases are in the right terminals or not, and would it matter in which order they come out of the breaker as long as they are matched up the other end? And would this cause a problem with the transformer or just the motor rotation?

Main thing here is the neutral is connected to the correct place, each phase to neutral is 230v. Phase to phase is 400v - (hate the new figures)

Thanks. neutral in the CU is connected to the neutral terminal block and measures 230v between N and the three phases coming from the breaker. I am going to get someone else to check the rest. But should be looking for the same in the isolator and the same at the end of the cable which will be connected to the new ramp?? If this is all correct then guess it should all work fine!

 

[mtkt29]

You do not say why the transformer went bang. Most likely is that a phase and neutral has been swapped and 400 volt was feed into something designed for 230 volt.

Thanks, not sure why the transformer went bang, but the guys installing the ramp said they are going to replace it free of charge. I see what your saying with over feeding the transformer voltage, but the machine was only on a matter of seconds! Or maybe this would only take seconds??

 

[ColJack]

photo's of the bits you're talking about would help us diagnose the problem...

many 3 phase supplies use the black core as an earth ( sleeved or taped in earth colours ) if the supply doesn't need a neutral ( which is often the case with motors. )

 

[Spark123]

"It would matter which way around you got the phases in the respect of your 3 phase motor will run backwards if it doesn't have the correct phase rotation".

Thanks for your reply. I know it is probably simple but how would i know if the phases are in the right terminals or not, and would it matter in which order they come out of the breaker as long as they are matched up the other end? And would this cause a problem with the transformer or just the motor rotation?

Would be a problem if something could be damamged by the motor running backwards, it is impossible to say which way around they need to be without checking phase sequence as to move a machine from one building to another can have different results!
Phase rotation wont be a problem to your transformer. What voltage is the transformer?

 

[ColJack]

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 )..

 

[mtkt29]

Thanks Spark123 you are being very helpful. Think the transformer is 230v but am going to check with the manufacturor. Think the issue maybe the neutral is being connected to a phase terminal coming out of the isolator.

 

[ericmark]

Phase rotation fault will not blow a transformer.
In your case three reasons it may blow,
1) Over voltage
2) Too high of current draw on output
3) Faulty transformer
Either of the first two could be called an electrical fault.
From what you say seems three phases and neutral correctly connected.
Which leaves the too high of a current on output. This should have been fused in some way and it would seem the installation guys know in there heart it was something they should have checked.
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.
To return to standard three phase they would change all links in every motor to star and change transformer supply to phase to neutral supply.
Although if not altered the motors will burn out they may last 15 mins or so and first thing to go would be transformer.
It is common where garages are not supplied with three phase to use an inverter and the type which produce 230 volt three phase are cheaper than type to produce 400 volt three phase.
If I was the guy commissioning the ramp I could also have missed that and if I did I would not want to admit the fault as I should have found it.
Have they removed covers from motors? Can you peep at plate on motor and see the two voltages and are they 230 and 400? And if they have not touched the motors are the links connecting three terminals together or three sets of two terminals together the former is the higher voltage.
Will watch with interest for reply
Eric

 

[Spark123]

I take it you are talking about a 230v input?
If the transofmer primary is 230v then it must be connected between a phase and neutral, it doesn't matter which phase it is connected to - so long as it is only connected to one of the phases.
If it has been connected between two phases then it will more than likely blown it, so a new one is in order and hope that it hasn't damaged anything else.