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Discussion Starter · #1 ·
Hello all, and thanks for all the wonderful help this community offers! I posted this in Electrical as well, I'm sorry for the duplication!

I just purchased a Senville mini-split system for my garage - it is a 24,000BTU unit that runs on 208/230 volts (Model is "Senville SENL-24CD")

I've done a bit of electric in my time, half of my house and the entire garage, but I've got a question about wiring the outdoor unit to my breaker panel. In doing some research, there is varying advice on what size cable and what size/type of breaker I will need for this.

The label on the outdoor unit has the following information on it, which is supposed to inform the type of cable and breaker I need:
1) Power Source: 208/230V - 60Hz
2) Indoor Fan Motor Load: .5A
3) Outdoor Fan Motor Load: .6A
4) Compressor Load: 15A
5) Indoor Minimum Circuit Ampacity: 3.0A
6) Outdoor Minimum Circuit Ampacity: 20.0A
7) Indoor Max. Fuse: 15.0A
8) Outdoor Max. Fuse: 25.0A

So, in running power cable from this outdoor unit to my breaker box, here are my questions:

1) I'm assuming that since it runs on 220, I will need a double-pole breaker, yes?

2) What size breaker do I need? The minimum/maximum numbers are confusing - why are the indoor and outdoor maximums different? Isn't the entire system going to be powered by one double-pole breaker? I've seen lots of variability, with people using anything from a 15-amp breaker to a 30.

3) Cable - I've seen lots of advice what wire I need to run between my outdoor unit and my breaker box. It will be about a 50' run of cable. I've seen people suggest 14, 12, or 10 gauge copper. 14 certainly seems small, no?

4) Is the cable for this going to 2-wire or 3-wire? Again, if it's 220, wouldn't I need something like 14-3, 12-3, or 10-3? (This would have the red and black wires going to the two poles of the breaker, with the white to neutral, ground to ground). I've seen people discussing just using something like 12-2. That doesn't seem right.

Thanks in advance!

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3,257 Posts
I recommend running 10/2 and using a 2-pole 25 amp breaker.

It will be conservatively rated and not taking advantage of the fact that you could actually get by with 12/2 wire and a 25 amp breaker and still be code compliant. You don't need to go the short route since you're doing a new install. If you had an existing 12/2, then that would be a different deal.

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8,194 Posts
1) Yes. A 2-pole that is factory handle-tied, not a duplex. However if you want to get really, really picayune into technical trivia, 2 singles with a field-applied handle-tie will be alright.

2) The *generic* answer is: "Whatever the instructions say, fullstop. If they're silent, then you need to look at nameplate ampacity and multiply by 125%." But I agree, the "indoor"/"outdoor" thing is confusing. Is it possible they want you to run your own power separately to indoor and outdoor units? (the outdoor unit is doing all the heavy lifting, so gets the bigger line).

3) That will be dictated by the breaker:
15A = any size (at least #14)
20A = #12 or larger.
25A-30A = #10 or larger.
You're always allowed larger.

4) Generally, you only need -3 (3+ground) if the appliance needs neutral for some reason. (Dryers need it for the tumble motor; ovens need it for the light). However water heaters and A/C units generally *don't* need neutral.

If they don't need neutral, and you're not expecting your next appliance to need it either (and I wouldn't with an A/C or heatpump), then you can use /2 cable and mark the white wire with black or red tape to indicate it is a hot. That marking is mandatory. Note that you can't use NM-B (common Romex) outdoors, not even in conduit. You can come through the wall into the back of a junction box *and that's it*. Then you transition to UF-B, or THWN in conduit.

I've heard it's a Code requirement these days to have a 120V receptacle reasonably near the outdoor unit, for the convenience of maintainers (to run freon vacuum pumps, that kind of thing). Maybe someone can confirm.

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