Saffa
Member
Yes to mainly DC inputs, and all DC outputs, but most of my rack PLC projects have one 120 AC input card to monitor fused power, and if the PLC runs on a UPS to know if the incoming power has failed.
I would always use an interposing myself for this kind of thing. But i generally would only be monitoring 1 or 2 such things in a panel. For our installations typically have a "mains fail" indicator which is either a 3 phase monitoring relay or a standard 230V coil relay for single phase installations.
I do mostly water utilities work, and all our control systems are 24V powered, with a minimum of 12 hours battery backup.
Guess it's different for most other industries.