QUESTION
General question about the standard or regulations involving how a pull cord e-stop circuit is wired.
Can a pull cord circuit be wired through a PLC for a stop command to be implemented, or does it have to be hard wired back to the contactor of the starter for the conveyor motor?
Are both acceptable?
REPLIES
itsmoked
You want it to be as fundamental as possible. A PLC could spaz-out and ignore a signal. It could respond correctly but have a hardware output failed ON which maybe is causing the need for an emergency stop, etc., etc.
You would want it going to the motor contactor in series with the starter’s coil circuit, any other safety switches, E-Stops, over temp, anything. You can also send it to the PLC so it realizes the motive power has ceased and handles it correctly.
If you have a VFD involved instead of a contactor you’d use new Safe-Torque-Off (STO) inputs found on most now, to disable the VFD output at the most fundamental level, below even the VFD’s internal computer.
SOURCE
https://www.eng-tips.com/viewthread.cfm?qid=466395
Above is a snippet.