NFPA(NEC) 70 Article 725.49(B) pertaining to class 1 cicuit conductors says "Insulation shall be rated for system voltage and not less than 600 volts"
Here I have two queries related to field I/O wiring for PLC/DCS systems ( e.g digital I/O at 120 VAC and analog I/O at 24V DC - 4-20 mA)
( i ). Is 600 V insulation mandatory if signal cables voltages/currents are not to exceed 120 VAC/5A and signal cables are adequately segregated ?
( ii ). Can typical DCS/PLC I/O fields signals be considered to be class 2 circuits even if a 24 VDC field power supply vendor or a 120 VAC vendor mentions that they do not have class 2 cicuit rating on their product ? ( I checked with a couple of well known power supply vendors ).