# 2HP Motor Current Imbalance



## Big John (May 23, 2010)

Roll your phases: A→B, B→C, C→A.

It will keep the same rotation, but if you've got the perfect mismatch between winding impedances and phase voltage imbalance, that might explain some of the current imbalance.

By rolling you might remove some of that.


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## John Valdes (May 17, 2007)

Did you measure the voltage with the motor loaded?


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## Electrorecycler (Apr 3, 2013)

John Valdes said:


> Did you measure the voltage with the motor loaded?


Yep. Voltages were taken with the motor under load (normal operating conditions). The only thing I haven't done is measure the voltage at the motor itself. All measurements were taken in the panel.


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## Big John (May 23, 2010)

Electrorecycler said:


> Yep. Voltages were taken with the motor under load (normal operating conditions). The only thing I haven't done is measure the voltage at the motor itself. All measurements were taken in the panel.


 At the very least you want to go to the load side of the last switch in the circuit.

It would take a catastrophically high conductor resistance to cause that type of voltage imbalance, but bypassing all the upstream equipment is a quick way to eliminate a lot of possible causes.


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## telsa (May 22, 2015)

Electrorecycler said:


> Yep. Voltages were taken with the motor under load (normal operating conditions). The only thing I haven't done is measure the voltage at the motor itself. All measurements were taken in the panel.


The only voltages that 'count' are those right at the pecker head -- or at least close by.

Checking the voltages at the panel is a total waste of time. They have no meaning.

They'd look okay if you had a flaming open in your circuit.

I'd STRONGLY suspect that you have been 'single phasing' -- to some degree -- and have issues between the panel and load.

A marginal connection -- at a terminal -- within the contactor -- even the heaters -- will drive you nuts.

Because the troubles will 'shape-shift' all over the place. 

Motors generate back-EMF. This means that it's easy to mistake back-EMF voltage induced during single phasing with merely being a strange low voltage reading.

This corn fusion happens all the time. 

ALWAYS suspect single phasing when a three-phase motor inexplicably runs really hot -- and overloads pop. That's its signature -- it's 'tell.' 

You must go all the way through the circuit to see what's up.


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## Electrorecycler (Apr 3, 2013)

telsa said:


> The only voltages that 'count' are those right at the pecker head -- or at least close by.
> 
> Checking the voltages at the panel is a total waste of time. They have no meaning.
> 
> ...


Can't disagree with you on that one. My suspicion is that we're dealing with a break in the wire somewhere. It wouldn't be the first time.

The issue seems to be intermittent, there are two of us monitoring the situation on and off throughout the day. With unbalance motors running vibrating tables in close vicinity, the constant vibration may be causing the few strands that are left to make and break. Chances are that we'll replace the cable from the disconnect to the motor this afternoon...after I measure the voltage at the motor :thumbsup:


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## ELECTRICK2 (Feb 21, 2015)

Electrorecycler said:


> Can't disagree with you on that one. My suspicion is that we're dealing with a break in the wire somewhere. It wouldn't be the first time.
> 
> The issue seems to be intermittent, there are two of us monitoring the situation on and off throughout the day. With unbalance motors running vibrating tables in close vicinity, the constant vibration may be causing the few strands that are left to make and break. Chances are that we'll replace the cable from the disconnect to the motor this afternoon...after I measure the voltage at the motor :thumbsup:


Sounds like the time it took to change the contactor gave a loose connection a chance to cool off and work properly for a while. Once it heated up and increased the impedance the problem is back. I'd bet it's in the pecker head.


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## JRaef (Mar 23, 2009)

Did you check the connections in the peckerhead? What I've seen that acts like that is a connection that is rubbing against the side wall until the insulation wears through. Sometimes it vibrates to a position that makes a high resistance ground fault to the side wall.


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