Originally Posted by
Eric Arnsdorff
Mike I agree that if you only look at steady state and assumed the voltage at the motor was exactly the same as ideal (120/240). But the first thing is the line losses leading up to the motor will be more in the lower voltage case and the V/f variances will cause differences. Additionally, my use of all motors in my shop are much more in a transient than steady state constant load case which cause even more differences.
I completely agree that it is completely functional if you only have the lower voltage. But there are a number of reasons why you get improvements using the higher voltages.
The differences you mention are in the circuit feeding the motor. If the circuits are properly sized so that the voltage drop during startup or running is the same percentage in either the 120V or 240V case, the motor will perform exactly the same and have the same heat characteristics.
The problem is that the circuit feeding most motors running on 120V does not meet that requirement so you get better performance on 240V.
Theoretically, they're the same. In real world situations, 240V operation often works better because of the circuit.
In general, I prefer to run any motor over about 1.5HP on 240V.
Mike
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