I am troubleshooting a 480 V 3 phase A/C condenser that tripped a circuit breaker; I'm showing continuity between the A and C phases on the unit. I have resistance tested the 2 fan motors and they are good. I tested the compressor and got 65k ohms A-B and C-A, and 3k ohms B-C. The compressor is currently disconnected but I'm still showing continuity. There is a 240v crankcase heater that I haven't tried disconnecting yet that I believe may be the cause for the continuity, and I'm pretty sure the winding in the compressor is the cause for the tripped breaker.
MrGus480
Continuity between phases
2 reading
The numbers make no sense.
Its no surprise to see low ohms between 2 legs especially as the controls are low voltage so somewhere there has to be a transformer.
As for a 240v crank case heater that makes no sense. why wouldn't they use a 480v crank heater. If it is correct then that means a second transformer or a second feed to the unit which would be on a different breaker.
Tell us the proper readings so we can calculate loads. It may be a motor then again it may be the heater is shorted but with out real numbers its nothing more than a guessing game. If you honestly got 65k across the compressor something is wrong with the motor or your meter.
Also tell us when the breaker tripped. Did it trip when the unit was off, starting, running.
Its no surprise to see low ohms between 2 legs especially as the controls are low voltage so somewhere there has to be a transformer.
As for a 240v crank case heater that makes no sense. why wouldn't they use a 480v crank heater. If it is correct then that means a second transformer or a second feed to the unit which would be on a different breaker.
Tell us the proper readings so we can calculate loads. It may be a motor then again it may be the heater is shorted but with out real numbers its nothing more than a guessing game. If you honestly got 65k across the compressor something is wrong with the motor or your meter.
Also tell us when the breaker tripped. Did it trip when the unit was off, starting, running.
Don't megger between windings, meg em each to ground. And listen to Tesla. Disconnect everything and test your continuity again. And then megger the feeders to each other after you are sure you got all the connected stuff disconnected. Non destructive ohm testing the windings with your multimeter not a megger, see if one is odd compared to the other two .
Continuity tests with megger show infinite resistance to ground, fluke didn't ring out when testing to ground either. Retested across compressor leads with fluke using alligator clips and got the same numbers as yesterday; possibly due to resistive qualities of oil and refrigerant.
The contactor for the compressor was stuck in and conductors show signs of arcing, soot deposits on the insulation near terminations.
The contactor for the compressor was stuck in and conductors show signs of arcing, soot deposits on the insulation near terminations.
Rule of thumb.
On a 3 phase unit readings should be close to equal, reading across all 3 phases A-B B-C A-C. Readings may run from .5 to 100 ohms but should be equal.
If not equal it is bad, most common is one set is open or half or twice the others.
Cowboy
On a 3 phase unit readings should be close to equal, reading across all 3 phases A-B B-C A-C. Readings may run from .5 to 100 ohms but should be equal.
If not equal it is bad, most common is one set is open or half or twice the others.
Cowboy
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