current imbalance

[maguire]

I have an phase current draw imbalance on a motor , rotation is ok and voltage on a;; three are good all the way down stream, at the motor connections I get 6,3.5,6 amps respectively can /would a contactor issue create this this is a new motor,
Devlin

 

[TicklyT]

Just because a part is new doesn't necessarily mean it isn't faulty. You would hope it has been tested in the factory, but....

How about moving all three phases around at the motor (1-2, 2-3, 3-1, to preserve the rotation direction), and see if the imbalance moves with the wiring, or stays where it is on the motor?

 

[ColJack]

stupid question but where and how are you measuring the current?

clamp meter on the motor tails?
sounds like the "middle" phase is the low one?

if you don't isolate the wire your testing then you can get some strange readings as the other phases cancel out some of the current..

move the wires away from the bunch when you are testing if you can..

failing that, try tightening the screws on the control gear, a loose screw = high resistance connection..

 

[maguire]

Coljack Hi spot on, you got me thinking I knew the motor connections were ok and I went along the phase feeds and checked them in and out of the contactor, overload device etc, and on the centre one the terminal screw was stripped tight enough to pass a cursory check but, I stripped it out and sure enough there was hardly any thing left of the pin mounts to the overload from the contactor new units one the way, thanks.
Devlin

 

[ColJack]

2 hours spent tracking down a very similar fault after I was sent to reconect a motor that had been sent away for rewinding after the previous sparky saw the same sort of results you saw..

wired it in, ran it, still playing up so I checked the voltages ( didn't have a clamp with me at the time.. ) and all seemed ok with the motor disconnected but no volts on one phase at the motor with it connected..
changed the wire and still the same..
eventually heard a faint crackling from the overload when the contactor pulled in and traced it back to a loose screw between O/L and contactor..