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Class 1 Circuits....

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midniteinak

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I've been digging for information on when a circuit must be marked as a Class 1 circuit...

For instance, PLC circuits, which are fed off the cards and generally powered from the backplane/power supply which is not marked as a Class 2 or 3 power source and generally falls under the 30V/1000VA ratings... and could definately be considered as remote control and signalling...
So, would these be required to be marked as Class 1 or is it an optional marking?
 
Yes, Class 2 and Class 3 equipment is almost always marked, with a few exceptions... Class 1 equipment on the other hand is typically not ever marked. In fact, there are no equipment marking requirements, only Class 1 circuits are required to be indentified per NEC 725.10. Also, per UL508a, a Class 1 circuit has to have certain markings applied to it as well. While in my opinion, these circuits could be considered Class 1 circuits, I have never seen a UL508a listed PLC panel come into the field marked that way. In fact, I've never seen a Class 1 circuit marking used anywhere. I tend to disagree with the statement that I have to assume these are Class 1 circuits, but I still am not certain what definately IS required to be marked as one.
 
A class one circuit uses chapter 3 wiring method, but the difference between it and power/lighting circuit is for the class 1 circuit no derating is required for conductor fill unless above 10% of the conductor ampacity.
But now that I think of it I have not see a PLC cabinet (UL508A) marked with the wiring type for field inputs and outputs. Inside the PLC cabinet 24 vdc is typically run with 120V...
 
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