I'm working on a project that has e-stop pull cords around the full length of a conveyor system which is about 750 feet long and it has 16 e-stop pull cord stations (8 per side). Due to the length, I'm looking at using 120vac for the e-stops and to avoid too much voltage drop by going thru all the e-stop contacts, I'm looking at running each e-stop signal back to the control panel and using it to activate the coil of a cube style safety relay. I'm then wanting to loop a 24v signal thru a contact of each relay and use it to activate a monitored safety relay which then activates the coil of a safety contactor to run my motors. So essentially I have 16 relays in my panel that mirror the state of each of the 16 field e-stops.
Here's a diagram of my idea (the actual design has 16 e-stops, 16 relays, and a PLC-controlled contactor after the safety contactor to activate once a reset button is pressed): https://i.imgur.com/2Qo5JQT.png
I've got a few questions though because I feel iffy about this setup.
Here's a diagram of my idea (the actual design has 16 e-stops, 16 relays, and a PLC-controlled contactor after the safety contactor to activate once a reset button is pressed): https://i.imgur.com/2Qo5JQT.png
I've got a few questions though because I feel iffy about this setup.
- Do I even need to bother with the relays or would voltage drop not be an issue here?
- Is using the e-stop contact to active a safety relay and using the relay's contact as my actual safety contact allowed? I'm thinking what if the relay contact welds?
- Related to (1), the relays are DPDT so if I used them as dual channel, would this help against the welding issue by having the monitored safety relay use dual channel inputs? Essentially, if the relay does weld, do both contacts stay closed when the coil is de-energized or just the welded contact?
- How are e-stops located far away from the control panel normally done?