Powering Discrete Inputs
Powering Discrete Inputs
(OP)
What are your views on powering plc inputs either from the field device or from the plc cabinet. Example being you kill the power on an mcc bucket if the plc input is powered from the bucket you'll have no other power source in it, if it were powered from the plc cabinet and you killed the power to the mcc bucket there still would power present in the mcc bucket. I looked through the NEC on this and couldnt really find, does NEC have anything on this situation?





RE: Powering Discrete Inputs
Control or signal power that originates from any other source other than a source controlled by the local disconnect switch should be treated as a secondary source. At the minimum I would make signs or plaqards that indicate that if the local disconnect is open there may still be voltage present.
RE: Powering Discrete Inputs