Pneumatics and Control Wiring

[kwired]

Bob

I can see the logic with conduit but not necessarily with tray.

If you had a pneumatic Thermostat line run in a conduit with a fault in it,it could melt a hole in the air line and you would loose temperture control of those units or unit.

Why take that chance?

Here is the way I see it, when a cable assembly is installed as a cable it lives by the rules of it's own article, when it is installed in a conduit or raceway it must comply with conduit and raceway installation rules such as derating and adjustment rules, conductor fill rules, the notes of chapter 9, 300.18, and 300.8.

I don't see where we get to change any of these rules because we are using a cable or conductor that does not have to be installed in a raceway on it own.

Let me ask this, does a cable assembly disperse heat inside of a conduit as well as it does installed outside of a conduit?

Roger

I don't see any rules that are being changed.

300.3 Conductors.
(A) Single Conductors. Single conductors specified in Table 310.13(A) shall only be installed where part of a recognized wiring method of Chapter 3.

If using conductors specified in 310.13(A) they will be installed in a raceway.

Raceways are required to be continuous between outlets, pull boxes, cabinets, etc.

I am talking about any kind of enclosure, trough, tray, or whatever you can think of that you may wish to run electrical cables as well as other things such as air tubing through.

As far as heat if you have cables bundled together with no other systems involved you still have to derate for number of conductors bundled together so why not here also?

If you do have heat involved from other systems then you need to derate for whatever the ambient temperature is. No different than derating conductors in a raceway that is installed in a boiler room.

 

[stevenj76]

If you are doing a retrofit, and it was that way when you got there, then it can stay.

Now, if you plan to pull-out ALL the pneumatic, you can re-use the raceway. This does not include pneumatic tube gutters.

Otherwise, you're on the hook to run your own conduit.


The problem with retrofits hasn't been sharing conduits, IMO. It has been that the HVAC bozos are reusing the old P/E class 3 power supplies fused at 10 amps to power their equipment which should be protected at 4 amps.

 

[petersonra]

An example of what I am referring to would be a machine with several air actuated devices on it as well as proximity sensors, limit switches, etc. to sense presence of material before an air actuator makes its move. There would be nothing wrong with routing cables for sensors as well as air lines through a leg of the machine that happens to be hollow inside - as long as the cables are not required to be installed in raceways otherwise.

Single conductors of type MTW would not be allowed to be installed this way, they would have to be installed in a Ch 3 wiring method and the raceway would need to be complete from junction/device/pull box to the next junction/device/pull box.

I think a good argument could be made that such wiring is not part of the premises wiring but part of the machine and thus not really subject to the NEC.

 

[kwired]

What if not a listed machine, maybe something fabricated on site, I would think NEC would apply even if not considered a part of premesis wiring.

 

[petersonra]

What if not a listed machine, maybe something fabricated on site, I would think NEC would apply even if not considered a part of premesis wiring.

Most custom made machines are not listed. The control panels for them can be listed, and often are.