View Full Version : Phase Loss.

31-08-2017, 03:48 PM
I have a compressor that will run for a minute and then the starter will trip due to a phase loss. My initial thinking is that a contactor in the starter is bad, however my troubleshooting ability for electrical components is not very sharp. Would someone please help guide me to a possible cause for my problem.

31-08-2017, 05:33 PM
Check the phases and measure the amperage being drawn.

Glenn Moore
03-09-2017, 10:37 PM
Is this a single or 3 phase compressor

The Viking
03-09-2017, 10:59 PM
First check the voltage of each phase entering your unit, Ph to N if you got N there otherwise Ph to earth.
Then do the same check at the entry terminals to the starter's contactor's.

Assuming the above checks out OK, check between the phases.
Again if you find the expected voltage in the tests above, isolate the unit and disconnect the leads from the compressor terminals, making sure that they are safe but also easily accessible with a test probe.
Turn the power to the unit back on and start it up then measure the voltages at the end of the compressor leads as above.
Isolate the power to the unit again.
If the above tests turned out OK, measure the resistance across the windings of the compressor and also from the windings to earth. (Down to earth a "Mega Ohm" or insulation tester is preferred but if a multimeter is all you got then it is better than nothing)
Reconnect the leads to the compressor and measure the voltages on the compressor terminals as above when the compressor tries to start. Also put an Amp clamp on the leads to the compressor, one at a time, and see what amperage each individual phase pulls. (You might have to reset and try to start the compressor several times to take all the measurements)

Happy Hunting.


04-09-2017, 04:04 AM
I prefer to check between the input phases ie l1 and l2 and l3 and getting voltages of 380 or above and starting at thé entry from the incoming supply,then following it through to both sides of the contactor.

05-09-2017, 01:24 AM
If all 3 phases voltage are normal check Phase loss relay it may possible that power is okay but due to defective relay or its setting system gives you a indication of phase failure.
Take care while working on controls and if you are not good enough in Electricals better to check by an expert.

05-09-2017, 01:25 AM
Voltage should be measured between
Check how the PLR has connected.