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Ref : NFPA(NEC) 70 Article 725.49(B).

Question asked by jz2018 on Feb 8, 2019
Latest reply on Feb 8, 2019 by rcramereleceng

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 ).

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