NEC 430.72 vs NEC 725.41(B)

[Isaiah]

Just to be sure, conductors from the secondary side of a CPT in a combination motor starter are NOT considered Class 1 remote control and signaling circuit as per 725.41

 

[tom baker]

If you fuse a motor control circuit it becomes a Class 1 Power Limited Art 725 circuit. The advantage is you can use smaller control conductors.

 

[Isaiah]

Thanks Tom! So the fused side of the 120V CPT constitutes a Class 1 circuit for motor control? Can you please specify the exact section?

 

[Jraef]

725.41(B) makes it a Class 1 Remote-Control and Signalling circuit, then 725.43 sets the OCPD requirements.

Keep in mind the NEC sets forth 2 different types of "Class 1" circuits: Power Limited and Remote-Control and Signalling. Power Limited requires a special power source and is limited to 24V (technically 30V, but nobody uses that). Remote-Control and Signalling has no special power supply rating, and can be up to 600V, which is where your secondary of a CPT fits. Both require OCPDs though.

 

[Isaiah]

725.41(B) makes it a Class 1 Remote-Control and Signalling circuit, then 725.43 sets the OCPD requirements.

Keep in mind the NEC sets forth 2 different types of "Class 1" circuits: Power Limited and Remote-Control and Signalling. Power Limited requires a special power source and is limited to 24V (technically 30V, but nobody uses that). Remote-Control and Signalling has no special power supply rating, and can be up to 600V, which is where your secondary of a CPT fits. Both require OCPDs though.

That’s what I thought, but its nice to hear it from the true experts.
Thanks Jraef!


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[Isaiah]

725.41(B) makes it a Class 1 Remote-Control and Signalling circuit, then 725.43 sets the OCPD requirements.

Keep in mind the NEC sets forth 2 different types of "Class 1" circuits: Power Limited and Remote-Control and Signalling. Power Limited requires a special power source and is limited to 24V (technically 30V, but nobody uses that). Remote-Control and Signalling has no special power supply rating, and can be up to 600V, which is where your secondary of a CPT fits. Both require OCPDs though.

I am curious about the phrase “functionally associated” in reference to 725.48(B).
I assume the danger is accidentally wiring field devices (I.e.HOA, Stop Start, etc) to the wrong motor starter if there are multiple 480V branch motor circuits and associated controls in the same conduit? Or is there something else?


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[tom baker]

See attached for how Mr Holt explains this

 

[Isaiah]

So the diagram on the right has a dedicated 120V CB, (Line and Neu) to the M coil/control device and therefore it is deemed "Remote" Class 1; whereas the other diagram does not have an external CB (or fuse) for the M coil and 430 applies?

 

[tom baker]

Yes once you fuse the control circuit and its not a tap you move from Art 430 to Art 725. Important concept here is tap.

 

[Isaiah]

Yes once you fuse the control circuit and its not a tap you move from Art 430 to Art 725. Important concept here is tap.

Great Tom
Would you say the reasoning behind having only “functionally associated” motor power and Class 1 control wiring in the same conduit relates to the possibility of connecting to the wrong starter at the MCC?


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[tom baker]

Not sure about your reasoning. My thoughts are its to localize a fault to one motor. Or to prevent uding that raceway for other circuits such as receptacles...