Discuss 3ph fridge problem. in the Commercial Electrical Advice area at ElectriciansForums.net

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Hello Guys. Got a situation here. Installed a 3 phase circuit for a commercial fridge. Bang a 20 amps 3ph Type C MCB at C.U and wired in the fridge via a comando 16a socket. switched on fridge and we rolling. After a week Fridge people turned up to do some more work. Something went wrong and they blew up the compressor on the fridge. They took pictures of the comodo socket showing apparently that L1 has been wired in Neutral and Neutral wired in L1.

Question : Can anyone tell me if interchanging the wires as such will actually blow up the compressor. I am suspecting that they have swaped these wires to try and pass the blame.

Regard

IA
 
In short, if the motor is three phase which I suspect is the case given that the supply is, then yes, you could have done serious damage to the motor.
I too can only ask how this wasn't picked up on your testing, we all make silly errors as such from time to time and that is why we ensure through testing that we have done things correctly, given the cost of repair, their callout and possible spoiled food, this could be a very expensive lesson and no doubt won't bode well if this is a regular customer.
 
Hello Guys. Got a situation here. Installed a 3 phase circuit for a commercial fridge. Bang a 20 amps 3ph Type C MCB at C.U and wired in the fridge via a comando 16a socket. switched on fridge and we rolling. After a week Fridge people turned up to do some more work. Something went wrong and they blew up the compressor on the fridge. They took pictures of the comodo socket showing apparently that L1 has been wired in Neutral and Neutral wired in L1.

Question : Can anyone tell me if interchanging the wires as such will actually blow up the compressor. I am suspecting that they have swaped these wires to try and pass the blame.

Regard

IA
If what the Refrigeration Engineer has said, is the case then effectively the motor would be minus 1 phase, on a 3 phase machine this would be the cause of the damaged compressor, in actuality the motor or more correctly the windings in the motor would have, either tripped out, or burnt out, you said in your post "I switched on the fridge we rolling" I guess what you mean the fridge started up, did it run properly, was it making a humming noise (not the normal motor noise) how long was it left running, more importantly what do your test results show on completion of the work?
 
This is really a case of you say I say. The posts previous to this say it all, we will not be able to satisfy your curiosity in this matter.
 
Ive never seen a motor start on 2 phases, only keep running with light load if it looses one.

Somebody is telling porky pies
 
The Motor had 1ph connected to N so between 2 sets of windings you would have 400v and between these and the 3rd winding you would have 230v, this could have seen the motor operate but not last long as it seems to be the case, some motors can actually run and start on 2 phase even with a phase out but it would depend on the motor, its duty, its starting arrangement and how its windings are configured.
I would be interested to why the motor was able to run until it failed as usually even in a phase loss, the motor overload protection would take over although I am aware alot of products do have basic overload monitoring without phase out protection and this may not have seen the situe due to the raised potential on the 3rd phase as it was strapped to N.
 
It would be 400 across 1 winding and 230 across 2 windings.

More importantly it could have had 400 across the control circuit if it used N for that.

I'd be slightly suspicious as it lasted a week before failing.
Who put the plug on?
Who commissioned the fridge originally?
 
I've never tried it but I would expect a motor with one line terminal connected to neutral to be more likely to trip its O/L or burn out than if the line were simply disconnected. When a motor loses one line, it runs as a single-phase machine between the other two but regenerates the missing one at approximately the normal voltage and phase angle. At light load this can continue indefinitely (although on a compressor I would expect it to go into heavy overload as soon as head pressure starts to build up). But if the third line connection is made to neutral, although it now has all windings energised, the voltage imposed on it by the neutral will not match the one it is regenerating in phase and magnitude, and the difference will cause a heavy current to flow limited only by the machine and supply impedance, much like a transformer with a partially shorted secondary. Paradoxically, I think it would be more likely to start than a motor missing a phase, but more likely to trip the overloads immediately afterwards. If there is insufficient protection, I would expect something to get fried pretty quickly!

I cannot imagine anyone would commission a 3-phase S/O without verifying correct connection, so at this stage perhaps we have to take the OP's sabotage theory at face value.
 
I'm pondering this one too Lucien, but given 1 strong field and 2 weak and there will be still a rotation of the fields I can see this running very inefficiently struggling to build the pressure up but possible limiting current rise but overheating to boot which can vary how long it lasts, akin to put 230v 3ph on a motor still connected as star 400v, I have known these to run for days/weeks before burning the motor out or indefinately if the load is low regardless of correct overload protection.
Whatever the circumstances of the OP, I know from experience that its possible what the fridge guys say may be true, we also don't know the circumstances of the timeframe, its possible the fridge has only just been put into service a week later or it did burn out a week before but no-one needed to access it for a week, so I take the time frame with a pinch of salt.
 
This is interesting, but I don't see how there would be a rotation of the fields with two of them, the weak ones connecting through neutral. Surely it wouldn't start full stop, never heard of this scenario so maybe I am misunderstanding the "theory".
Interesting to know if there is single phase control circuitry because there is only a three to one chance either of it either having 400v across it or being reverse polarity.
 
Normally the single phase equipment in a 3 phase machine is fed from L1.
If L1 and Neutral are reversed, it should not affect the single phase equipment.
Swapping L2 or L3 with Neutral however, would have caused 400V to flow through the single phase equipment.
 
Even a relatively small voltage imbalance would lead to a much larger current imbalance. The copper losses in the motor would be enormous in the circumstances you describe. Copper losses = heat. The compressor should have tripped on its klixon which measures the temperature of the compressor body as well as being a thermal electrical protection device.

A post mortem of the compressor windings would easily show if the damage was caused by voltage imbalance.

Even if there was a large voltage difference across different windings the compressor protection should have prevented catastrophic failure.

My personal take is that the motor would have lasted minutes, not days, if one of the phases was connected to neutral and the protection should have operated in seconds.
 

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