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
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??
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.
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.
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
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
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!!
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.
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).
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
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.
Yes, this is similar to the problem at
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.
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.
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