UL508A Wire Gauge Questions

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Mcamnl

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I am a little confused on the issue of wire gauge when it comes to UL. I know it says a min. of 14ga. for power circuits. I understand this to include powering things like motors and 24dc power supplies. What about things like the coil side of a relay? Solenoids? I understand the rules apply the same for 24vdc circuits also. Does a 24vdc relay coil need to be wired with 14 ga.? Power to a PLC?

Sorry for all of the questions.
Thanks for your help
 

dbaird

Member
Location
Dayton, OH
Relays and Solenoids are usually found in control circuits and not power circuits (although I suppose they may occasionally be found there).

I would review UL508A section 2 Glossary on "power circuits" and "control circuits" if I were you. Look at their examples in Figures 6.1 thru 6.3 and try to determine if your circuit is a power circuit or a control circuit.

I personally prefer to follow NFPA 79 Electrical Standard for Industrial Machinery 2007. Section 12.6 covers conductor sizing.
 

Mcamnl

Member
We are just getting started as a UL panel shop. Before that we just wired the panels using the NEC as a guide for gauges and other stuff.

So, for example, we have a contactor that is used to start a 2.5 HP blower motor. The coil on the contactor is 120vac. So this would be part of a power circuit and needs 14ga to the coil?

Or, in another machine, with relays, we control solenoids in different parts of a building. These are 24vac solenoids. 14ga all around or just on the solenoid side?

Thanks for all of your help.
I will go over the referenced parts of the 508A code.
 

dbaird

Member
Location
Dayton, OH
Mcamnl,

I can not give you a definitive answer without reviewing your circuit schematics, but my gut feeling is still that your relay, contactor and solenoid coils are in the control circuit portion of the circuits. The contacor's contacts to power the motor would be in the power circuit.
 
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