PLC I/O device & NEC 725 Class 1 wiring

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steve8440

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Example Situation: I have to design 24VDC power & I/O wiring from PLC control panel and field terminal box via trough or cable tray. Since the 24V, 10A power supply (in the PLC panel) is not a listed Class 2 device, the wiring defaults to Class 1 and I am planning to use 600V tray cable. In the field, a factory assembed cable with connector is installed from the field terminal box to the sensor (e.g. prox switch, pressure transmitter). However, this cable is rated for 300V and is #22AWG which doesn't meet Class 1 rules. Back at the control panel, the PLC I/O cards are wired to a terminal strip using a multi-conductor 300V cable as well.

Do Class 1 wiring rules (e.g. 600V insulation, #18AWG minimum per NEC 725) apply to the device cordsets and PLC cabinet I/O wiring in this situation?

If the same situation occurred, only this time the equipment (PLC, trough, wiring, devices) are all mounted on a skid as a piece of equipment, does the NEC even have jurisdiction under NEC 90.2 or would this make it subject to NFPA 79 (or other?) instead?

Thanks in advance.
Steve
 
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