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Small 120/240 Volt 3phase 5hp grinding pump that is triping on overcurrent.  FLA = 13.2 Amps/phase. The utility has a
voltage imbalance of 1.8%, but the current imbalance is 28%...Can anyone explain????

RE: Imbalance

Hi dpEng,

Whenever you get a problem like this it means more energy is being dissipated somewhere and the problem is finding out where. I don't like the imbalance in the currents but under overload conditions it's not a safe evidence of a motor fault. Have you tried running the motor without the pump. That's the easiest way of eliminating one half the possible causes.

RE: Imbalance

Is the voltage balance the same at the motor terminals?

Search this site for “unbalance” or “imbalance.”  It has been extensively discussed here.  

RE: Imbalance

Suggestion: Check the motor windings.

RE: Imbalance

Sounds like you have a motor problem, but you could try rotating the phases as connected on the motor. Usually, there is a combination that minimises the imbalance. At light load, a small imbalance in supply voltage can result in a much larger imbalance in current. This has been discussed before. If the imbalance is occuring with the motor loaded, then you could have a shorted turn or similar.

Mark Empson

RE: Imbalance

See FAQ's in this section. It talks about rolling the leads and discusses where this imbalance originates from. I think there is a definate problem with the motor or the wires going to the motor to have this much current unbalance. Good luck.

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