Field Wiring

We have a couple electrical circuit design tools that I was trying to use for a current project on some controls wiring but both packages only go down to 14 AWG.

These are primarily made for commercial and industrial electrical work and not so much controls but is there a reason not to run 16 AWG THHN in the field?

The control panel wiring is 16 AWG MTW. Is 14 AWG as small as your supposed to pull through conduit in the field?

Anyone? Is it ok to run wire than 14 AWG to field devices? I was planning to use 16 AWG.

What is the smallest you would want to use and pull through conduit?

On the machines I build I run 16AWG wire from the panel to the sensors and small current draw components (solenoid valves, lights, DC conveyor motors, etc.)

I have even worked on machines where wire as small as 20AWG was used, but I wouldn't go that small - I don't even buy wire that small for use on controls.

If your converter tools have the NEC "programmed into them" then that is probably why 14awg is he lower limit since it given as a lower limit for wire size calculations in at least one of the parts of wire size calculations. But, I think that rule is under the assumption it is a feeder from a breaker at household voltages. I believe your PLC I/O and other field devices protected at a lower level are not subject to those same charts and calculations of the law that the software tools are based upon.

I think running 14awg THHN for a panel of buttons or to any proximity switch would serve no useful advantage over 16awg.

I am not a code expert, this is my opinion.

the program is probably designed on the side of caution for liability reasons.

we have run 18 ga wire hundreds of times to field devices.

what you must consider it the wire length, amperage, voltage drop.
those factors determine what is required.

regards,
james

These are primarily made for commercial and industrial electrical work and not so much controls but is there a reason not to run 16 AWG THHN in the field?

Click to expand...

Yes, there is a legal reason if your facility generally follows the U.S. National Electical Code, then Article 310.5 Minimum Size of Conductors says:

"The minimum size of conductors shall be as shown in Table 310.5.

 

Table 310.5 Minimum Size of Conductors

 

Conductor      | Minimum Conductor Size (AWG)

Voltage Rating | Copper | Aluminum or Copper-Clad

0 - 2000           14              12

2001 - 8000         8               8

15,001 - 28,000     2               2

28,001 - 35,000   1/0             1/0 

However there are 10 exceptions to the rule that allow for smaller control and signal wires.

It depends on what you are using the conductors for, how they are classified.

If the conductor is being used as general wiring, then as Lancie pointed out, 14AWG is the minimum size. But, if the conductor is being used as a remote-control and signaling conductor then it could be classified as a Class 1 conductor which allows 18AWG and 16AWG under 725.49. The allowable ampacities for the Class 1 remote-control and signaling conductors fall under 402.5, 6 amp for 18AWG and 8 amp for 16AWG.

I normally use 14 AWG for 120 volt control wiring and 16 awg for 24 volt. If there is a long run (200+ feet)of 24 volt wiring, I go to 14 AWG for voltage drop (just a general rule of thumb).