I have a project that I'm doing the automation for and wanted to throw my scenario out there to see if anyone could offer some advice/suggestions:
The project involves multiple smart MCCs, meaning each motor's MCC bucket has a motor management controller. These controllers are all connected to my PLC via Modbus...so I have no hard-wired outputs for motor control. There are multiple e-stop stations throughout the plant, that are wired back to my PLC panel(s), however, the customer did not account for a hard-wired e-stop circuit and expects me to use the PLC for an emergency stop. Even though in a recent call to my local MSHA office, I was told that they have no regulations for a full plant e-stop just individual machine e-stops, it's my company's policy (and my personal policy) that we NEVER program in a PLC-controlled e-stop. There is way too much risk and liability involved in this.
First off, I know the PLC-controlled e-stop situation has been discussed multiple times before. Can anyone direct me to any legal literature or guidelines that explain the dangers behind this? My customer isn't buying the "it's my company's policy" thing, and I'm being pressured by my GM (who knows nothing about the automation side of our business) on why we have this policy in the first place. I would like to be able to give them all some official document backing my stance so they'll get off my back.
Secondly, does anyone have any suggestions on any possible way for me to do an approved e-stop circuit in this situation? The customer has pulled back the wires from every remote e-stop station to my PLC. I'm ignorant when it comes to safety controllers and safety relays. Can I wire the e-stops through a safety controller or relay and communicate that back to my PLC in some way? Is that permissible? Short of killing power to the PLC during an e-stop, I don't know what I can do on my end. I've told my customer that the e-stop circuit needs to be wired through each motor bucket and showed them on the MCC schematics where the manufacturer accounted for a customer-supplied e-stop, but they didn't like to hear that and would like another solution.
Any help would be greatly appreciated!
The project involves multiple smart MCCs, meaning each motor's MCC bucket has a motor management controller. These controllers are all connected to my PLC via Modbus...so I have no hard-wired outputs for motor control. There are multiple e-stop stations throughout the plant, that are wired back to my PLC panel(s), however, the customer did not account for a hard-wired e-stop circuit and expects me to use the PLC for an emergency stop. Even though in a recent call to my local MSHA office, I was told that they have no regulations for a full plant e-stop just individual machine e-stops, it's my company's policy (and my personal policy) that we NEVER program in a PLC-controlled e-stop. There is way too much risk and liability involved in this.
First off, I know the PLC-controlled e-stop situation has been discussed multiple times before. Can anyone direct me to any legal literature or guidelines that explain the dangers behind this? My customer isn't buying the "it's my company's policy" thing, and I'm being pressured by my GM (who knows nothing about the automation side of our business) on why we have this policy in the first place. I would like to be able to give them all some official document backing my stance so they'll get off my back.
Secondly, does anyone have any suggestions on any possible way for me to do an approved e-stop circuit in this situation? The customer has pulled back the wires from every remote e-stop station to my PLC. I'm ignorant when it comes to safety controllers and safety relays. Can I wire the e-stops through a safety controller or relay and communicate that back to my PLC in some way? Is that permissible? Short of killing power to the PLC during an e-stop, I don't know what I can do on my end. I've told my customer that the e-stop circuit needs to be wired through each motor bucket and showed them on the MCC schematics where the manufacturer accounted for a customer-supplied e-stop, but they didn't like to hear that and would like another solution.
Any help would be greatly appreciated!