VFD Over Current Protection
VFD Over Current Protection
(OP)
I have a C-H MCC with a section containing a 50 Amp circuit breaker and a C-H VFD dseigned to control a 25HP motor, all new, not yet powered. Turns out the device being powered has a 10HP motor. Any problems? I am thinking of NEC motor protection.
Thanks;
Steve
Thanks;
Steve





RE: VFD Over Current Protection
Is there a PTC sensor (thermistor) fitted to the VFD or is it relying on electronic thermal characteristics?
The issue is not just over current protection but motor thermal protection.
I would check with C-H to determine if this meets class 20 protection for the motor if using purely the electronics of the drive to protect.
RE: VFD Over Current Protection
Thanks;
Steve
RE: VFD Over Current Protection
That said, some VFD mfrs have a restriction as to HOW MUCH smaller the motor can be, because of the resolution of the type of current sensing devices they have on the output. Some use cheaper methods than others. I have seen some that limit the motor to no less than 1/2 the rating of the drive, so in this case, 10HP is below that threshold. But it varies from mfr to mfr, A-B PowerFlex drives for instance have no such restriction, you can program a 400HP drive to protect a 1HP motor if you want to. So only C-H can answer that for you, or it will say so in the manual if you look up the programming of the motor FLA.
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