Quote:
Originally Posted by xrated
I've been a Journeyman Electrician for over 40 years and it's not unusual at all to see something like an A/C unit pull 3 to 4 times the normal running current at start up. Simple math on that would be 45 to 60 amps. It's called LRA....Locked Rotor Amperage. The rotor is dead stopped when the power is applied, so the inrush of current in that couple of milli-seconds will spike very high. The good news is that within the first instant of power being applied, the rotor starts turning and the current dies down to the normal running current. All this happens in milli-seconds of time. Larger 3ø motors will sometimes peak out at 7+ times of the FLA (full load amps) on start up.
Another factor that can be involved is short cycling of the compressor. When the A/C compressor shuts off at the end of a cooling cycle, the refrigerant inside the cooling loop will take a bit of time to equalize. If that equalization doesn't completely equalize, and the compressor tries to start again, the starting current will go even higher than the normal 3 to 4 times of FLA. Hope that helps understanding it.
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I've racked in some high voltage motors, 1320, and hit the start button. It takes longer than you would think for them to get to speed. We always had to call the Utilities Control Operator first. You can just feel the juice.