Art 725

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Isaiah

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Baton Rouge
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Electrical Inspector
Can I legally run 480VAC 3Ph power to a Motor along with Class 1, 120VAC control and Class 2, 24VDC discreet signal (to DCS) in the same conduit as long as they are ‘functionally associated’ and insulted to 600V?


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Isaiah said:
Can I legally run 480VAC 3Ph power to a Motor along with Class 1, 120VAC control and Class 2, 24VDC discreet signal (to DCS) in the same conduit as long as they are ‘functionally associated’ and insulted to 600V?


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Depends on more details. If you are pulling individual conductors through a raceway, probably can not pull the class 2 conductors inside the same raceway in most cases. If you are pulling listed cable assemblies through a pipe/tube/etc (would not even need to be a "NEC raceway" then you can have all three together. Might be design reasons you shouldn't or at very least use cables with shielding if there may be interference on signals being carried.
 
kwired said:
Depends on more details. If you are pulling individual conductors through a raceway, probably can not pull the class 2 conductors inside the same raceway in most cases. If you are pulling listed cable assemblies through a pipe/tube/etc (would not even need to be a "NEC raceway" then you can have all three together. Might be design reasons you shouldn't or at very least use cables with shielding if there may be interference on signals being carried.
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Here, they only use single conductors in rigid galvanized steel conduit. Part of the run will be buried PVC conduit in red concrete duct bank. The 480V runs to a 2HP motor with 3 #10 AWG w/#10 ground from the MCC.
The 120VAC Class 1 circuit and 24VDC discreet signal cable at Class 2, originate from a local control cabinet and both are unshielded #14AWG.
For some reason this client stopped using cable tray with TC cable some years back.


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Isaiah: Please read all of 300.3 C 1. This section is often mis-understood as few read the entire section.
This post back if you are allowed to do what you are proposing.
 
ActionDave said:
As long as you use chapter 3 wiring methods, which it sounds like you are, and relabel the 24V power supply I think you are ok
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Actually, what you say is only part of what is necessary. You can run the wiring if you reclassify the entire circuit and use Chapter 3 wiring methods. This requires removing the Class 2 marking from the power supply. But that also means that all of the sensors, loads and controls attached to that power supply CANNOT require a Class 2 limited power source.
 
Isaiah said:
Can I legally run 480VAC 3Ph power to a Motor along with Class 1, 120VAC control and Class 2, 24VDC discreet signal (to DCS) in the same conduit as long as they are ‘functionally associated’ and insulted to 600V?


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725.41(B)(1) allows running all the #14’s in the same conduit with the 480V power to the same motor/controller using 600V insulation. Art 430 part VI will cover the 120V control circuits. No de-Rating of the 14AWG is required as long they’re limited to 1.5A capacity.
Very few clients’ specifications will permit this sort of installation even though it is NEC compliant.


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ActionDave said:
As long as you use chapter 3 wiring methods, which it sounds like you are, and relabel the 24V power supply I think you are ok
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Most DCS and PLC power supplies are Class 1. The 24V I/O is Class 2, but the cable insulation has to be 600V due to the Class 1 power supply.


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Dale001289 said:
725.41(B)(1) allows running all the #14’s in the same conduit with the 480V power to the same motor/controller using 600V insulation. Art 430 part VI will cover the 120V control circuits. No de-Rating of the 14AWG is required as long they’re limited to 1.5A capacity.
Very few clients’ specifications will permit this sort of installation even though it is NEC compliant.


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I meant 725.48(B)(1)— typo


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Dale001289 said:
Most DCS and PLC power supplies are Class 1. The 24V I/O is Class 2, but the cable insulation has to be 600V due to the Class 1 power supply.


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But like Golddigger mentioned not far back, once you essentially turn it into class 1 you must reclassify the entire circuit, not just the parts of the circuit that is convenient for you. That means all items connected to that circuit are now class 1 and you can not use any device or methods rated for class 2. You can use relay isolation to go back to class 2 if that can work for you though.
 
Special thanks to Tom and Dale.
I feel confident about allowing this installation to proceed.
Kwired: wouldn’t the 24VDC Input/Output act as the relay you’ve noted?


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Isaiah said:
Special thanks to Tom and Dale.
I feel confident about allowing this installation to proceed.
Kwired: wouldn’t the 24VDC Input/Output act as the relay you’ve noted?

Unless the individual i/o outputs are tested and listed as Class 2 power sources, the fact that the power supply to the PLC is Class 1 governs the entire installation. A dry contact output which is used with a separate Class 2 supply might qualify as the necessary isolation.
The basic question is not whether the PLC outputs are Class 2 or not. If you want to run wires attached to those outputs in a circuit reclassified as Class 1 so you can combine the wires with power wiring in the same conduit, then whatever the output is driving must NOT be limited to use in a Class 2 circuit.
If you reclassify input wiring to the PLC as Class 1, then the PLC must not rely on the inputs being Class 2 or dry contacts for safety.


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Since PLC and DCS power supplies are usually class 1, wiring from the I/O cards must be insulated at 600V in order to run in the same raceway with power/120V control and still be Code compliant.
Most clients specifications however prohibit combining AC with DC circuits even if the signals are discreet.
I see no need for relabeling if all circuits are correctly insulated and functionally associated.


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Isaiah said:
Special thanks to Tom and Dale.
I feel confident about allowing this installation to proceed.
Kwired: wouldn’t the 24VDC Input/Output act as the relay you’ve noted?


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It can, but is in wrong location in relation to the class 1 and power conductors you are wanting to isolate from. You need to make it so the 24 V conductors are reclassified as class 1 circuit and put a relay at the other end of the run before continuing on with any class 2 wiring. That wiring beyond would have to have a separate class 2 source somewhere driving it and the relay is just a switch or coil that interposes with a class 1 circuit.
 
kwired said:
It can, but is in wrong location in relation to the class 1 and power conductors you are wanting to isolate from. You need to make it so the 24 V conductors are reclassified as class 1 circuit and put a relay at the other end of the run before continuing on with any class 2 wiring. That wiring beyond would have to have a separate class 2 source somewhere driving it and the relay is just a switch or coil that interposes with a class 1 circuit.
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Thanks Kwired. Can you note the specific code section that addresses this?


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Isaiah said:
Thanks Kwired. Can you note the specific code section that addresses this?


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725.136.

You can not run class 2 circuits with class 1 circuits or power circuits. You can convert the circuit to a class 1 circuit somehow, but must convert the entire circuit not just a section that is run with class 1 or power conductors, or use some sort of conversion like a relay to convert back to class 2 before you continue with class 2 wiring methods again.
 
kwired said:
725.136.

You can not run class 2 circuits with class 1 circuits or power circuits. You can convert the circuit to a class 1 circuit somehow, but must convert the entire circuit not just a section that is run with class 1 or power conductors, or use some sort of conversion like a relay to convert back to class 2 before you continue with class 2 wiring methods again.
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Thanks Kwired!


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