Reno,
A T-stat circuit is absolutely a "Remote control" circuit. And since the T-stat is not built into the appliance and is a separate device the conductors between the T-stat and the A/C unit would be a remote control circuit and the power supply for the T-stat would most likely be a Class 2 power supply.
Chris
I do not see any reference in the code to 'remote control.' Yet, since the air conditioner requires both parts (cnndenser and evaporator), as well as the thermostat, to operate, it seems clear that the thermostat circuit -wherever located- is integral to the air conditioner.
The code section cited refers only to circuits that are not integral. As i read it, I can run the thermostat wire, but not the household phone wire, along with that power circuit. If the system is monitored (perhaps operated from a remote location), then the phone/ data circuit could also be in the sealtite, as it would then be an integral part of the air conditioner.
Field installed control wiring is not an integral part of the unit. It is a necessary part to make the unit work. So is the branch ciruit supplying power to the unit. The control wiring does not even need to be conductors between the indoor and outdoor unit. One could use some wireless device on each end to transmit signals and a short cable on each unit to its wireless device. There are devices available to convert 2 or 4 wire cable to 6 or even 10 wire applications without changing the cable.Originally Posted by renosteinke
If you read instructions for the unit, it likely says to install the field control wiring to local codes as well as the branch circuit up to the unit.
The Title of Article 725 is Class 1, Class 2, and Class 3 Remote control, signaling, and power limited circuits.
And as far as integral to the A/C unit that would require the T-stat to be factory installed in the A/C unit such as with a room air conditioner that is a factory built complete unit. An A/C unit that is part of a central air system that requires a separate T-stat and control circuit that is field installed would be a Article 725 circuit and need to follow the rules for the Class of circuit.
Chris
I do not see anything in ther NEC that restricts 'integral' to components within a single enclosure.
Indeed, the plain meaning of the term, as found in Webster's, is: "essential to completeness : constituent <an integral part of the curriculum."
Thus, I consider the thermostat and it's wiring to be integral to the air conditioner. I believe this is exactly why the code excludes such a circuit from the scope of 725. Also. as I cited, the scope of the article makes no mention of 'remote.' Whatever other descriptions may be used elsewhere, if it's not in the scope, it's not part of the article.
Give us some examples of what is a 725 application that is not very similar to low voltage controls for typical heating and cooling units. These control circuits are usually essential to completing the installation and making the equipment usable.
Sorry, but that's not my problem. There's the general points that the code panels need to say what they mean to say, and that the readers refrain from trying to twist the code into saying what they think it ought to say. (My favorite example of the latter is the sudden Home-inspector driven concern over Romex in crawl spaces, ever since the code took romex out of 'damp' locations).
Though, I suppose, one could speculate someone running the phone wire, just for convenience' sake, through the same wire trough as the power wires in an industrial setting. That is, phone wire for the usual phone systen, rather than a similar looking data line that was used to control or monitor the equipment.
Just what, exactly, is the hazard posed by putting a low voltage wire in with a power wire? I think that is the concern here- along with understanding just what a 'power limited' circuit is for.
Induced voltages? So what? OK, I can see a desire to have the insulation rating be high enough that it's not compromised. Otherwise, the only circumstance where you would have an issue where the simple presence of voltage might fool a computer into thinking it was getting a control signal. This can happen with a PLC, but not with a relay; the induced voltage won't power a relay.
The 'separate the control from the power' doctrine can get really silly when the control circuit is using the exact same voltage as the power circuit; there are plenty of 'control' circuits using 120 volts out there. Even some thermostats. Trouble is, 120v on a thermostat wire looks just like 6v on a thermostat wire. Pictures may not lie, but they sure can leave out such details.
There's the concept of 'power limited' circuits to consider. In brief, these are circuits that have transformers whose impedence is so high as to limit the amount of current they can deliver. A dead short on the output side of the transformer will, by design, result in the transformer getting very hot, even failing .... a design deliberately choses to prevent the transformer from delivering too much power down the line. While this might be real important on an 'intrinsically safe' circuit in a hazardous location, I can't see much relevance for the household heat pump.
I'm going to 'return to the real world' to -again- put this all in perspective. Let's look at a household 'mini-split' system. You have the condenser outside, and an evaporator inside. The power for the evaporator comes from the condenser, and the thermostat is mounted near the indoor unit. This means that you will have, running from the outdoor unit to the indoor unit, a set of HVAC tubes, a thermostat wire, and a power cable. Since they start and finish at pretty much the same places, it's certain they'll be run together. Some would have you believe that you can run that thermostat wire right next to that piece of romex for fifty feet .... but have an objection to running them together through the same sleeve of flex for the two feet between the house and the outdoor unit. That objection is just plain silly.
I would like to thank all that responded. I was a construction electrician but due to the economy I am now working as a building maintenance man. I bring this and many more questions up to my boss. I am repeatedly told that I am wrong. I am looking for the true intent of the NEC. I followed the conduit down from the roof penetration to the open space above the ceiling tile.(This area has HVAC duct returns so my understanding is this is not a plenum ceiling). The juntion box (4" square or in my juristiction a 1900 box) where the feed for the roof top disconect switch terminates has an open 1/2" KO where the #14 THHN temperature control conductors. These are the control conductors that are in the same EMT raceway as the #10 THHN power feed conductors for the condenser. The same control conductors are spliced in the disconect switch then they are installed in a sealtight whip to the condenser where they are terminated]are then spliced to thermostat wire. I believe at this point the temperature control circuit becomes a class 2 circuit. At the juntion box where the control conductors are spliced the power conductors are encased in EMT back to the panel board that feeds the circuit[I believe this to be a class 1 circuit]. The temprture control conductors [in the same juntion box that connects the raceway system to the RTU are then run in free air[that is no conduit] to the thermostat which is a 24 Volt class 2 device. So my question is are a class 1 and class 2 wiring method allowed in the same raceway. That is to say I have a 208 Volt 3-phase system class 1 power circuit feeding the condenser. Also I have a seperate 24 Volt class 2 control circuit for temperture control in the same conduit. I believe I have two seperate systems in the same raceway. I also have an equipment ground bonded to the juntion box beneath the roof that passes through the disconect switch and is terminated at the condenser equipment ground lug. Should the EGC be bonded to the disconect switch at the roof feeding the condenser? My understanding is that you can not run a class 1 and class 2 circuit in the same raceway as the class 2 device[in this case the thermostat as the thermostat can not handle a 208 Volt potential?
This is the oddest thing I have read in a while.
The unit will not operate without a branch circuit either but that does not make the branch circuit an integral part of the appliance.
My only objection to that is that NM cable would be installed in a wet location. Replace the NM cable with UF cable and nothing wrong with that installation.
Running the power circuit through a raceway for 50 feet with THHN/THWN and the control circuit is not allowed. There is no rule stating a power limited control circuit can't be run next to a cable wiring method such as NM cable. You could even run the control circuit through same hole exiting the structure that contains the service entrance cable supplying the structure.
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