Pull cords & Conveyors
Pull cords & Conveyors
(OP)
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?
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?
RE: Pull cords & Conveyors
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.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Pull cords & Conveyors
There are also lower level safety relays that can likely be used with a pull cord. Some of them actually negate standard 'normally closed' e-stop failure modes that aren't generally expected.
EDMS Australia
RE: Pull cords & Conveyors
And yes, I should have mentioned that this conveyor is/will be VFD driven.
I guess I am set in my ways of its predecessor which had a multi-conductor teck running along the length of the conveyor, picking up devices (side travel, horns, pull cords, etc.) which were all wired back to the control wiring in the softstarter's e-stop circuit. I trusted an open circuit to stop a soft start more than I would trust a PLC to stop a drive.
I was thinking that there would be regulations for the wiring method for this scenario, but I couldn't find very much specifying how it MUST be wired. (ISO, CEC, NFPA, Mining Act, even NEC)
Thank you again
RE: Pull cords & Conveyors
RE: Pull cords & Conveyors
Also we've had a lot of discussions on conveyor E-stopping. Loooooong AC safety circuits can have serious issues that need to be dealt with correctly.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Pull cords & Conveyors
RE: Pull cords & Conveyors
RE: Pull cords & Conveyors
Keith Cress
kcress - http://www.flaminsystems.com