Article 430.74

[duhhuh]

Sorry to be dense, but I am having a major mental block, so I would appreciate any input.

Where you have a starter that has a control circuit that is generated from the starter in Hand operation and in the Automated operation, the circuit is generated from the PLC, when the starter is in the "open" position, should all power sources be disconnected, specifically coming from the PLC? Or are you allowed under Exception No. 1(b) to put a permanent warning label stating that foreign voltage is present and stating the location of such.

Again, thanks for any insight and understanding.

 

[templdl]

Re: Article 430.74

What we did with our MCCs is to attach a Yellow warning label to the outside of the enclosure warning of a separate source power, the exact verbage which I can't recall. The color of that wire may also be different.

 

[earlydean]

Re: Article 430.74

Exception 1(b) to 430.74(A) is only where more than 12 motor control circuit conductors are required to be disconnected. Two or more disconnects are allowed, one for the motor and the controller, and the others for the motor control circuits. You would need two disconnects to handle your situation as described. And they would need to be mounted next to each other.

What we used to do where the computer operated the equipment from afar, would be to mount a small "ice-cube" relay next to the magnetic starter, which would provide a set of N.C. contacts to wire in series with the control circuit. When the computer wanted to load-shed the motor, it could shut it down without the PLC being a part of the motor control circuit.

Earl

 

[tom baker]

Re: Article 430.74

The ice cube relay is a good solution. It may be simpler to install an aux contact on the starter disconnect handle, so when its off, it opens the control circuit supplied from the PLC.
I use an interpoise relay cabinet, have 9 or so relays, perhaps 4 or 5 sources of control voltage in it, but each motor controller only has one source of control voltage, when its disconnect is off all voltage is removed.