Just came across a second panel this month where the PLC lost it's program due to a low battery & the power being dropped. On both machines the PLC was (keyword = WAS) powered by MCR power, not line power (I rectified that situation while I replaced the battery & reinstalled the program I had a copy of). I have never done this, as I figure the PLC should be on whenever the service disconnect is on, just use MCR power to supply most outputs, leaving some outputs line powered (Red stacklight, MCR enable relay, Buzzer, etc. but never any process items) with the PLC monitoring if MCR power is on. Also, this PLC had MCR power wired to an input & did check if it was on to run things, but if MCR power was off the PLC would be off.
What is the reason, if one, anyone would wire a PLC to MCR power?
Am I alone in this thought?
What is the reason, if one, anyone would wire a PLC to MCR power?
Am I alone in this thought?
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