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The label on the disconnect box says this is a 60amp, 240v system (box might be oversized for this unit, it's old and a 2 ton I think, I doubt that it's truly 60A). I know that I need 6awg for it, and the wiring currently is in metal conduit on the outside of the wall. The run itself is only about 15ft (plus or minus a few inches) to the main electrical panel.

[edit] The AC unit is an UAKA-030JAZ, and the label lists itself as says that it is minimum 19/19 (not sure what the double number means, honestly) ampacity. Looks like this is a 2.5ton. I'd expect if/when it needs replaced to be replaced with a larger unit. I don't think any of the new homes of this size built around here are less than 3.5ton.

I will have opportunity to put this in-wall when I repair some of the siding at some point this summer.

Does the code (US, Texas) allow for in-wall wiring for the condenser? Does it have to be in conduit, if in the wall? What wiring do I need to purchase for this?

[edit] Is there any reason not to go with a heavier gauge wire, considering that the cost is minimal, it possibly future-proofs, and I might need to drill slightly larger holes? Both Home Depot and Lowes offer 15ft and 25ft sections of NM 8/3 and NM 6/3, not to mention the many places on the internet that I can apparently order this.

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[edit] Adding a photograph of the label on the main wiring panel, as requested.

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    You DO NOT need #6cu for this. A 2-ton A/C unit is likely less than a 20A draw. The 60A is just the maximum rating of the disconnect, meaning it can handle 0-60A. Apr 14, 2020 at 17:04
  • @SpeedyPetey That's what I thought. But I may upgrade this anyway, in case the unit needs to be upgraded in the future (I was told it was undersized when the AC guy repaired it a few years back). Even if I didn't do #6, most of the units I look at are saying #8. Would it make any sense to use that, and can I just use nm/romex for this?
    – John O
    Apr 14, 2020 at 17:42
  • I would not guess at the wire. Find out the "minimum circuit ampacity" and "maximum overcurrent or fuse" size and that will tell you what size wire and breaker to use. Apr 15, 2020 at 0:24
  • Can you post photos of the existing AC unit's nameplate? Also, please do not pull air conditioner sizes out of your rear end -- ACCA Manuals J and S weren't intended to gather dust.... Apr 16, 2020 at 3:06
  • Also, are there fuses in your existing disconnect box? Apr 16, 2020 at 3:08

3 Answers 3

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You could in theory do it inside of the wall, but the "device box" would have to a a Flush Mount 3R box, and that's not something I have ever seen for a simple AC disconnect. In other words you can't just exit the wall through a hole in the siding and run into the bottom of a surface mount box, and for all of the surface mount ones I have seen, you can't enter the box from the rear because that's where the disconnect device is. So although it COULD be done, I don't think you will find the hardware to make it happen (at least not to Code).

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  • There are knockouts in the back of the disconnect box (not knocked out yet) below the switch. Why couldn't I use those? Even if I had to have one of the conduit fittings for that, it would just extend into the siding. I could provide a picture of the disconnect box if helpful...
    – John O
    Apr 13, 2020 at 22:12
  • Most AC pullout disconnects I know of have a KO in the bottom rear section, yeah.... Apr 14, 2020 at 0:26
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Speedypetey is correct a 5 ton will only require ~30 amp disconnect and can be run on #10 wire. You can run the wires inside the walls if it is a cable with all the wires contained in a outer sheath conduit is not needed inside. If separate wires thhn/thwn it will need to be in conduit inside the walls. A standard 30 amp disconnect would be proper is there a 120v receptacle? Some of the disconnects I install have a separate 120v receptacle, very nice place for one if there is not one “in sight” as code requires.

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  • There's no receptacle. And I could switch out the disconnect box too at the same time, they're not that expensive I don't think. #10 would really be sufficient for even a 5-ton? Most of the things I've been reading on the internet (yeh, I know) talk about using at least #8 for the larger AC units.
    – John O
    Apr 14, 2020 at 19:33
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I would run a 1/2" ENT instead of a cable if I were in your shoes

If I wanted to future-proof this, I would run a 1/2" ENT inside the walls. This provides enough space for any feeder up to 50A circuit ampacity (given that most breaker and disconnect lugs are rated for 75°C, which lets us use 8AWG wire for the feeder), while leaving room still for a 15A branch circuit for the maintenance receptacle, if need be. If a maintenance receptacle is not needed, then said 1/2" ENT can handle a 60A feeder without trouble.

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