Electrical installation question

[Bob O 8]

I have an electrical installation question. Is it required to separate the ControlNet for communication, 24VDC for I/O and the 120VAC I/O into separate pipes when running from panel to panel? Thanks

[BobLfoot 301]

Not sure of the regulatory implications of your question, but in practice we run the CNET and 24DC I/O in one pipe and 120 in another when running panel to panel. The CNET is a coax and should be noise resistant, but check the manuals about intallation guideline before placing in an AC pipe.

[indepthmarine 0]

Not sure about US national electrical code, but Canadian Electrical Code (which closely mirrors US National Electrical Code) states that you can not mix voltages like this in the same conduit. You should even have a barrier in the enclosure(which is not really possible if the PLC is 120VAC power and the IO module is 24VDC) Best bet is to separate the 120VAC and the 24VDC in different conduits, and label each accordingly. The ControlNet is low voltage I assume, so can legally go into the 24VDC conduit. More work now, but you will be confident that nobody in the future will easily mix voltages on you and blow modules.

[paulengr 44]

If you are talking about "signalling" (not power), there's no direct issue. If you are carrying power of any substantial amount, standard practice is to isolate it from your signal lines. If you go too far with 120 VAC I/O, you can also get inductive pickup which will drive you nuts trying to troubleshoot it. You can also get "ringing" problems with 24 VDC if you use lots of mechanical relays, and a similar problem with 120 VAC circuits if the downstream devices don't draw much power and you are using triac (solid state) outputs. There's also a potential for an arc flash issue. You can ignore NFPA 70E altogether at least at the current time if the voltage is under 50 volts (AC or DC). So the standard practice with most folks in the last couple years has been to try to go to 24 VDC whenever possible and put the AC stuff in separate enclosures.

[Bob O 8]

Thanks. We do separate the 24 and 120 so this was probably more of a question just because it has always been done that way doesn't mean it should be done that way.

[Sergei Troizky 26]

Could you reffer to the specific paragraph of the code?

[dogleg43 1]

I cannot quote the NEC code section, but voltages may be mixed in the same raceway as long as ALL of the wires in that raceway have the same insulation rating. Now here can be your "out": the NEC does not apply to control systems, only premises wiring.