This is a great and timely topic that others and myself have been kicking around in the office for over a month. Please bear with me for a minute and let me know if you think this flies - I welcome all opinions and interpretations!
Here's my POV: If I'm interpreting the NEC correctly, as long as the control circuits can be classified as Class I circuits, then they can be run in the same raceway with the power circuit ONLY if they are functionally associated.
There is a discrepancy that is raised from this because 300-3(c)(1) apparently lets you mix ANY cables with the same insulation rating, with the exception of the FPN covering Class II and III cables. That section does not make mention of Class I cables having to be separate according to 725-26 (unless functionally associated).
There was an article in last month's EC&M confirming this - "Making Sense of the NEC's Rules on Industrial Controls." According to the author, all Class I circuits and power circuits must be totally separate according to the NEC (unless functionally associated). This apparently spells the end to the very common industrial tradition (still being practiced as I write this) to mix 600V insulated power conductors with 120V/125VDC/24VDC 600V insulated discrete control conductors all together in tray and conduit.
My opinion is this: I see the NEC's point in separating the controls from the power circuits. In the case of insulation breakdown, accident, whatever - you get 277 into a PLC discrete input or something like that and fry the equipment and/or the guy troubleshooting the controls (as pointed out also in an earlier post). But - at the same time, the NEC allows you to run power and controls that are functionally associated together where I believe you would have the greater risk of an accident - such as mixing up the power and control terminations at a starter, where you have a couple of multiconductors coming in the same conduit or some scenario like that.
So finally, from all this I would gather, CTwireman, the installation you referred to is kosher with the NEC if the A/C Unit's control circuits are Class I because they can be considered functionally associated.
[This message has been edited by SolarBear (edited 03-27-2003).]
