motor controller disconnect

[petersonra]

code requires motor controller disconnecting means. typically this is some kind of switch or CB that opens up power both to the motor and the starter. my reading of the code would indicate that power needs to be removed from the whole controller. usually this is accomplished by either an auxiliary switch off the disconnect or by powering the coil from a transformer, and since most installations seem to do it this way I am guessing my interpretation of the requirement is correct.

but when we have a vfd, the disconnect for the vfd typically removes line power, but i can't recall it ever removing control side power. often control power is supplied externally, sometimes it is 120V. are a lot of people violating the rule, or am I misinterpret ting the rule?

 

[jim dungar]

Re: motor controller disconnect

Bob,

The coil control circuit needs a disconnect but it can be seperate/different than the power disconnect. There is no requirement that they have to operate at the same time.

Many times there are some voltages present on auxilliary (non power circuit)contacts, these are often called foreign voltages. These voltages do not need to be disconnected at all. I like the practice of coloring these conductors yellow as suggested in NFPA79 and UL508A