Wiring codes/standards for small signal?

[adventurer]

I wonder if there are any codes/standards out there to address industrial equipment, specifically the small-signal control circuitry and wiring they often utilize.

For instance, I know that it is good practice, but is there a code or standard out there that actually says to keep AC and DC signal wires separate? And when wiring small signals such as to PLCs, is there a code/standard that specifies what wire sizes to use? The NEC doesn't really show anything above 18 gauge, which handles 18 Amps. What about color? Does it matter? Or issues such as strapping the wire or harness properly when running to a hinged panel, to avoid stressing the cables.

There are a ton of little issues that arise for which I've never seen a comprehensive guide/standard. What to do?

 

[xnuke]

The NEC does not say that 18 AWG can handle 18 amps. You should look that up in Article 725.

Also, NFPA publishes NFPA 79: Electrical Standard for Industrial Machinery that has a lot of useful information. If you're going to be manufacturing industrial equipment or control panels, I recommend it.


xnuke

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[adventurer]

Actually I was referring to Table 310-17 of the NEC for single conductors. The 90C-rated 18 awg conductors are rated at 18 amps at 30C. But don't get lost in the detail. The point I was making is that the NEC does not address any wire gauges smaller than 18. It is quite common to use 24 gauge wire in low-signal applications. I wonder, though, is there a code or standard that gives this type of info.

How complete is NFPA 79 in addressing the numerous issues that arise in industrial machine design? Does it, for instance, have ampacity tables for smaller gauge wires? Does it address the issue of running AC and small signal lines near each other?

Thanks.

 

[xnuke]

Okay, I see where you got the 18 amps...and my reference to Article 725 was incorrect for your application, since your cabling is an integrated part of the device.

For a rough idea of what NFPA 79 contains, you can view a draft here

http://www.nepss.org/NFPAtc79/draft_NFPA79_2002.pdf

but I highly recommend buying the 2002 standard. It's about $35 US.

xnuke

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[adventurer]

Thanks for the info. It looks like it has a lot of good info. I'll order one tomorrow.