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| Fundamentally, an electric motor's shaft speed is set by the frequency of the power. And the shaft load is set by the load. Tight belts lead to more friction load.
A motor can draw rated current with no shaft load if the voltage is high and the iron core is saturating.
A three phase motor can run hot with one phase drawing high current if the voltage is not balanced. That gets worse under load. Unbalanced voltages often are the result of open delta farm transformer connections and is made worse when the wild leg transformer is smaller than the main transformer.
As for low voltage, since the motor speed is determined by frequency and the load by the speed, the motor has to draw more current to produce the power when the voltage is low. Low voltage comes from undersized transformers out on the pole (most motors take at least a KVA per HP) or from long runs of wimpy wires on the secondary side and that includes the cord to the elevator from the panel.
You can check for core saturation by running the motor with the belt off and checking line current. If the voltage is not too high, the current should be significantly lower than the nameplate rating. Core saturation has been more of a problem with older motors designed for 220 volts running on 250 volts, thouogh if the WEG is designed as closely to the load as described by others here, it could have that problem.
You can check for voltage unbalance for the three phase motor with a good voltmeter, but the current unbalance will be about 6 times the voltage unbalance. Sometimes that unbalance can be coming from poor connections anywhere from the transformers to the motor.
Wires that by NEC will carry the current can be too small when voltage drop is a factor. Runs over 50 feet probably need to be the next gauge larger, at 100 feet maybe two gauges larger to keep voltage drop in reason. At that point connecting the wires to the right sized breaker and to the motor becomes difficult so its often better to mount a panel with large lugs close to the motor location so those service wires can be large and the smaller wires to the motor can be short.
Gerald J. | |
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Bad electricity...................and belt conveyors??
