Running RS232 in the same wire bundle as 230 VAC

I'm looking at mounting a B&B cellular modem on a control panel door. The modem connects to a FA-ISOCON converteing the RS232 signal to a RS485 signal. There is 1 bundle of wire connecting buttons, and temperature controller on the door to the rest of the control panel. In this bundle is 230 VAC (that's what the temperature controller runs off).

Will I get signal distortion and other problems with my RS232 communications if I run it in the same bundle with 230 VAC?

Thanks in advance.

Nearbyatom said:

I'm looking at mounting a B&B cellular modem on a control panel door. The modem connects to a FA-ISOCON converteing the RS232 signal to a RS485 signal. There is 1 bundle of wire connecting buttons, and temperature controller on the door to the rest of the control panel. In this bundle is 230 VAC (that's what the temperature controller runs off).

Will I get signal distortion and other problems with my RS232 communications if I run it in the same bundle with 230 VAC?

Thanks in advance.

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In my experience it is discouraged to run your comms wiring (RS232 cable, Ethernet cable etc) in the same bundle as your AC wiring. But I have seen them bundled together because it was the most convenient way to run the wires. There are other things that can cause problems with the RS232 signal, the length of the cable is important (the shorter the cable the better).

A_G said:

In my experience it is discouraged to run your comms wiring (RS232 cable, Ethernet cable etc) in the same bundle as your AC wiring. But I have seen them bundled together because it was the most convenient way to run the wires. There are other things that can cause problems with the RS232 signal, the length of the cable is important (the shorter the cable the better).

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I think they will run together for about 2 ft then I'll have them split up . Other wires in there are 24VDC control wires for switches and lights.

If the communications going through the cable aren't time dependent and can handle some packet loss (like panelview comms) then it's likely not a problem. If you're controlling something like a VFD, that's a whole different monster. I worked at an OEM that ran itself in circles for two months because the mechanical guys ran comms for 12 separate VFDs in the same pipe as all the 480 and the electrical guys didn't know.

I'm no NEC expert, but Article 725 does give you some recommendations and requirements for separation of different types of circuits in the same panel.


If it's possible to separate your AC power from your serial networking, you should. It reduced the probability of interference, especially if your heater controller is outputting PWM signal directly.

My career has plenty of highlights that include telling project managers and electrical contractors something to the effect of "I told you a-holes not to do that" when they disregarded my advice to not run Ethernet or RIO or DH+ through the same big conduit as the 480V power mains and/or high power servo and VFD cables.

It's less a matter of "there is an explicit electrical code that requires this" or "I can tell you with certainty that the serial comms will never work", and more of a "if you did it as recommended, we wouldn't be having this conversation."

When my control panel shop puts AC devices on the door (sometimes disconnects, often convenience receptacles) they route them in a separate bundle as far as practical away from the 24V DC and the network cables.

Ken Roach said:

It's less a matter of "there is an explicit electrical code that requires this" or "I can tell you with certainty that the serial comms will never work", and more of a "if you did it as recommended, we wouldn't be having this conversation."

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This 1000%. If I had a dollar for every time I had to tell someone this, I could be sitting on a beach somewhere .

When I built control panels I would have separate door harnesses for for each voltage 120vac DC and comm .. also makes trouble shooting easier ..