Contactor as disconnect means in control panel with multiple power sources?

[SirScott]

I came across an electrical print for a machine that has two sources of power entering it. A 208V 3phase with neutral feed into the enclosure via a disconnect switch with 3pole circuit breaker and then a 480VAC 3phase via a contactor followed by separate 3pole circuit breaker. The contactor coil is powered by the 208VAC circuit such that if you open the 208V disconnect switch, the 480V circuit contactor opens. I hadn't seen this done before so I have searched my NEC book and searched online, but have not found a definitive answer if this is legimate. Can anyone shed some light on this?

:?

 

[jim dungar]

Sure the installation, as you describe it, could be legitimate per the NEC. For the most part control circuits are simply design choices.

However, unless it is padlockable in the open position, the contractor will most likely never qualify as a required 'motor disconnecting means' nor as a LOTO point. It is possible that the breaker after the contactor could meet the disconnecting means.

 

[baymach]

not allowed

not allowed

I had designed exactly the same circuit in one of my enclosures. It did not pass field labeling. I had to install a disconnect outside the enclosure and label the enclosure door how it is supposed to be shut off and LOTO. Then it was good.