motor controller disconnecting means

[petersonra]

I have always felt that a motor controller disconnecting means needed to completely isolate the controller.

I started to think about this.

In the case of a motor starter being the controller, do you need to remove the voltage to the coil (via an xfmr or aux interlock switch)? This is pretty common so my guess is that this is indeed a requirement.

But with VFDs, when you open the disconnect to the VFD, you remove the power inlet to the VFD, and the power outlet to the motor, BUT potentially there is still some power source that could be feeding the VFD control lines. Why don't we disconnect these? Sometimes these lines are 120V.

 

[honeyfarmer]

Re: motor controller disconnecting means

you are talking about the control voltage ,yes ?
I think the intent is to isolate the motor so that it can be worked on .the VFD should be labeled with the power feeder cir. # and the control source for a quality job . We supply engraved tags
with this info on all diss.connects ,transformers ,panels ,you get the picture

 

[paul]

Re: motor controller disconnecting means

Also included in the labeling should be some sort of notification that it's fed by two or more sources and to disconnect ALL sources before working inside. I've done this with small motor starters that were 480V switched, but 120V control power. I don't like this sort of setup, but I've had to hook them up like this more than once. I'd rather see a combo starter with an Xfmr or a 480V coil. That way all power is off with the throw of one switch.

 

[augie47]

Re: motor controller disconnecting means

normally when we have a starter with seperate control voltage, we install an auxilairy switch in our disconnect (factory accessory)and feed the control power thru it