Motor protection with freq drive

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BKearney

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For a branch circuit with a fan motor (2hp/230v/3ph) and frequency drive, what type of protection is needed?

I always thought all I needed was a combination motor starter (then the freq drive and then the motor), some people say "fuse and contactor" or "breaker and contactor".

What section in NEC details this?
How can I be sure all I need is a motor starter if I am correct...or better yet, how can I prove this to someone?

Thanks in advance for your time!

Brian
 
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This is a design question, not an NEC issue. As petersonra said, all the Code requires is short circuit protection if the VFD has a listed overload protection function.
 
So I only need a breaker or fuses...

However, if I want to switch the fan on or off using a contactor (instead of some other method involving the freq drive), can I not just use a combination motor starter in place of the "fuse or breaker and contactor"?


Jim,
I also asked which NEC sections this info could be found...so I was thinking it was an NEC question...
 
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If you want to utilize a contactor to start/stop the fan, install a 2 or 3 contactor bypass package with the VFD. Usually you can get it already prebuilt and wired and ready to hang on the wall. The bypass contactor has the motor overloads in series with it to protect the motor. When using the VFD the motor overload program protects the motor.

A 2 contactor bypass does not totally isolate the VFD from all of the line voltage, so you would not be able to service it as you would be able to do on a 3 contactor bypass. but the 2 contactor is cheaper.
 
BKearney,

Remember you have to size the circuit for the VFD not the motor,also

switching a VFD on/off is usually a big no no by the manafacturer.

IMO, best bet is feed VFD use it's OCP and also use the switching function

in the VFD for your on/off stuff. JMO 430.122 and 430.124
 
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