Mixing thermostat and power wiring in same conduit whip (from disconnect to Heat Pump unit)

I'm replacing an old heat pump installation which had the thermostat wiring and the 220V romex all within the same plastic conduit whip going from disconnect to the condenser unit.
I understand thisn't acceptable per current code. I need a couple clarifications.
1. Can std. Romex wire be used in a conduit or does it need to be individual wires? (ie THHN) 2. It appears that thermostat wiring is permitted within a conduit if it's insulation is rated for the same voltage as the high voltage circuit. (ie CL1 220V). However can std. thermostat wire (ie 18/4) be contained in it's own small conduit within the main conduit??
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If you were a *competent*, licensed, insured, professionaly trained, HVAC technician, you would already know the answers to your questions. The answers you seek are in the NEC, and I believe also in the UMC Maybe you should check with you local building inspectors?? You *did* pull a permit, didn't you?? I will however give you some answers below...keep in mind that these answers are based on the requirements in my location.

Romex won't pass inspection here.... use properly sized THHN

Not allowed here at all

If its a heat pump, you will probably have more than 4 wires. Control wires should be in their own seperate conduit, period.
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If class 2 or class 3 power source is used then no raceway is required.
See nec article 725
Anyways, standard practice at least in my area is to route thermostat wire along with the copper lineset between the condensor and ahu--the outer pvc jacket holds up just fine under outdoors weather condition.
--





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You could run the low voltage with the line voltage if you use "line voltage" conductors, which will probably be rated 600 volts, and although 'THHN is often bantered about as the conductor of choice, keep in mind it is not rated for wet locations. Most, but not all conductors have multiple ratings, so for wet locations be sure it has a letter "W" in it like THWN

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Thats why its run in Carflex or Sealtite but then you probably knew that, right??
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Sealtite can be run in "wet" locations like underground, and when it is, THHN is not an acceptable conductor

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RBM wrote:

once a low voltage wire was contained in a conduit or raceway, it has to be treated as a line voltage conductor, even after it emerges from the conduit.
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In the heat pump there will be separate compartments for line and low voltage. He would have to maintain line voltage conductors until he's into the low voltage compartment. IMO it's not a practical way to wire the thing

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And you completely sure about this ?
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Noon-Air, get a life. So I guess you are a competent, yatta yatta, licensed blah blah. Go sniff some more freon!!
Howard, check with your inspector. If you can route the tstat wiring along the outside of the conduit that has the power wiring, just do that and buy some wire ties. Of course, if you need it protected because of animals, heathens, teenagers running weedeaters, then just run the flippin thing in another piece of flex.
Congratulations for doing your own work. It saves a hell of a lot of money and you won't rip yourself off like a lot of competent, insured blah blah contractors will, and you will do a better job then a lot of them. Go for it!!
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Actually I have been a contractor for over 10 years and add to that 22 years of training and experience in the military. Sniffing "freon"??? LOL....FREON is a registered trademark of Dupont Corp. Sniffing a trademark?? What an idiot.

Dumbshit... thats what I told him...

Yeah right... there are some parts of the country(US) where its ILLEGAL for unlicensed homeowners to do their own HVAC work. Even here in backwoods south Mississippi, if you DIY on an HVAC system inside of the city limits, after you have to rip it back out, and pay the fines, then pull a permit, get it reinstalled by a licensed contractor, and get it inspected, you would have been a whole lot better off getting it done right in the first place. But your too ignorant to figure that out for yourself.
Now Greg, Since your so eager to spout off, what is your profession?? are you in business?? How long have you been a certified Master of your profession?? What are the inherent hazards to your customers, their families, and their homes if you screw up?? How much training, education and experience do you have in your profession?? How much continuing education are you required to have to maintain your certifications?? Or do you really want to go there?? Maybe you should quietly go away.
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I'm not Noon-Air, you stupit fuck.
Suggest learn to post, moron....

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RBM wrote:

I believe mixing the power and control wires in the same conduit changes the Class 2 control circuit into a Class 1 circuit. A Class 1 circuit generally has to be wired as normal line voltage circuits - Romex, EMT, boxes; #18 may be used if appropriate. That would apply to all the control circuit connected to those wires, like the wiring to the thermostat. Control wires in the disconnect makes the control circuit Class 1 also.
Line and low voltage wiring can go to the same enclosure when connecting to the same device in that enclosure, like a relay.
You could probably mix UF (instead of Romex) for power plus a control cable in the same conduit (but I didn't look it up).
-- bud--
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I agree except I believe that once the class 1 conductors leave a class 1 location, they can be transitioned back to class2. For example, and air handler built by "First", instead of running class 2 low voltage into the unit and make connections on an isolated board, they run what appears to be MTW out of the machine and leave tails for connection to class 2 low voltage. Similarly, in any AC condenser, your class 2 conductors are connected to line voltage conductors before entering the line voltage compartment for connection to the contactor

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Look Guys....
As to your debating Class 1 or 2 or THHN or THWN or UF or whatever....
Running a control circuit in the same raceway as a branch circuit is a bad idea for reasons that have nothing to do with the code...
Low voltage, current limited control circuits can.. and have... generated all kinds of havoc when run in close proximity to branch conductors that might induce voltage into the control line.
Contactors can 'mysteriously' pick-up at odd times, OD temp. sensing is screwed up, solid state controls will go absolutely wack-o.
Jake
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Thank You Jake. Absolutely correct. Line voltage and low voltage in the same conduit or sealtite is a problem waiting to happen. Im glad you explained it in very simple terms. Bubba
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Bubba wrote:

the Hinsdale, IL telephone office a few years ago. Office personnel was pulling cables in the cable racks, when a flash (spark) occurred. They had Greenfield carrying AC and other large 48 volt DC in the same rack. Immediate investigation showed nothing. Of course, there are millions of wires in a telephone office, so it's like looking for a needle in a haystack. A few days later, a fire broke out on Mothers' Day evening when no one was in the building. And, these wires were not even in the same conduit, just the same raceway.
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sure would be nice if the ductless-mini-split manufacturers climbed on board. seems like they're all running Hi & low volts in the same umbilical cord....of course, WTF do they know....
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RBM wrote:

All the compressor/condenser units I have seen have a separate wiring compartment for connection to external class 2 wires. That sounds like the "First" unit.
Class 2 wires can be in the same enclosure with line voltage wires when required for connection to something like a relay. They stay class 2. There are some rules like for separation. Factory wiring inside the unit is covered by UL rules.
But wires can't mix in the same raceway. Then they become class 1.
-- bud--
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