DC powered motors' NEC compliance
DC powered motors' NEC compliance
(OP)
I am integrating process equipment where a 3rd party is suppling some of the equipment incorporating a few DC controlled motors, and their control boards. I am responsible for documentating the circuits they are on, starting at the load center.
It seems that this supplier is IEC EN61010-1 compliant but doesn't own an NEC book. Beyond fusing on the line side of the power supply there is no other motor protection on the DC boards. The supplied fuses are too large for NEC compliance of Overload or even Short Circuit in one case.
My question is, from the AC side of a DC motor controller, can I properly protect these motors. They are small - 450 Watts and 95 Watts. Given that 125% FLA of the motor (430.32 b(1) Overload protection) will be enough to power the boards. Can I translate the DC power delivered to an AC power and fuse accordingly. I am aware that efficiency and power factor are involved but in both cases would increase the actual current used and so my fusing would be low enough.
Thanks for any thoughts you might have.
Jason
It seems that this supplier is IEC EN61010-1 compliant but doesn't own an NEC book. Beyond fusing on the line side of the power supply there is no other motor protection on the DC boards. The supplied fuses are too large for NEC compliance of Overload or even Short Circuit in one case.
My question is, from the AC side of a DC motor controller, can I properly protect these motors. They are small - 450 Watts and 95 Watts. Given that 125% FLA of the motor (430.32 b(1) Overload protection) will be enough to power the boards. Can I translate the DC power delivered to an AC power and fuse accordingly. I am aware that efficiency and power factor are involved but in both cases would increase the actual current used and so my fusing would be low enough.
Thanks for any thoughts you might have.
Jason





RE: DC powered motors' NEC compliance
Just surmising, but I bet motors that small are impedance-protected for overload (or possibly thermally protected). AC supply side protection would only be concerned with short-circuit protection.
Let's see if anybody else sees something.
Best to ya,
Old Dave
RE: DC powered motors' NEC compliance
RE: DC powered motors' NEC compliance
Jason Bender
RE: DC powered motors' NEC compliance
I'd get an IM if you don't have one and be guided by that.
RE: DC powered motors' NEC compliance
RE: DC powered motors' NEC compliance
DC drives are current controllers. All they do is control current into the motor.
If you protect the AC line against short circuit or overloead then you are protecting the DC motor at the same current level.
Usually the fuses supplied on the DC drive are there only to protect the semiconductors. Do not consider them as part of your electrical safety circuit.
Most DC drives have a current limiting adjustment. this can be set to jsut above the current required for maximum output required by the application.