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Discussion Starter · #1 ·
I am running power to a 18000btu minisplit ac unit. It requires either a 15 or 20 amp breaker. The run is 60' from panel to the disconnect, which size wire do I want to run Romex 12-2 or 10-2 awg ? I am leaning towards the heavier gauge wire 10-2, is their any problem with that besides cost.
 

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It's more annoying to work with.
If the minimum circuit ampacity is less than 20A there is absolutely NO reason to use larger than #12 for only a 60' run.

What is your logic for running wire bigger than necessary?
 

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Discussion Starter · #3 ·
Some of the wire size calculators suggest that you go down to 10-2 if you exceed 75' on a 20 amp breaker. I was concerned of wire heating up under full loads. Does the fact that it is 220 make a difference. I appreciate your input. I tend to over kill but I don't want to under size this unit. Thanks again
 

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Some of the wire size calculators suggest that you go down to 10-2 if you exceed 75' on a 20 amp breaker. I was concerned of wire heating up under full loads. Does the fact that it is 220 make a difference. I appreciate your input. I tend to over kill but I don't want to under size this unit. Thanks again
75' at full load might be an issue with voltage drop at 120V, but not with a 240V circuit. Wire size calculators are not always the end-all be-all for wire sizing. Too many rules-of-thumb that may not be very accurate.

240V makes a difference with voltage drop, not wire size. VD at 240V is less of an issue than the same load at 120V.
 

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Discussion Starter · #5 ·
SP,

Just to recap, installing a 1.5 ton mini-split heat pump AC unit; Power supply (V, PHASE, Hz) 208/230,1,60 Max. Fuse size (time delay) (A) 15
What's time delay mean?
So I am running I believe a 2 pole 15 amp breaker, 60' feet from panel to the disconnect and you say Romex 12-2 awg wire will handle the required loads without any problem. Can I use the same wire unsheathed from the disconnect to the outside unit inside the whip? Or does that require THHN wire and if so why?
Carpenter by trade so a little out of my profession.....Your input is highly regarded. You are licensed electrician correct?

Thanks
Handle
 

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SP,

Just to recap, installing a 1.5 ton mini-split heat pump AC unit; Power supply (V, PHASE, Hz) 208/230,1,60 Max. Fuse size (time delay) (A) 15
What's time delay mean?
So I am running I believe a 2 pole 15 amp breaker, 60' feet from panel to the disconnect and you say Romex 12-2 awg wire will handle the required loads without any problem. Can I use the same wire unsheathed from the disconnect to the outside unit inside the whip? Or does that require THHN wire and if so why?
Carpenter by trade so a little out of my profession.....Your input is highly regarded. You are licensed electrician correct?

Thanks
Handle
Theoretically in this case you can even run 14/2, but 12/2 is fine and probably what I'd use.

Technically you cannot strip out NM cable and use the conductors as they are not labelled individually even though they are THHN.
 
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Theoretically in this case you can even run 14/2, but 12/2 is fine and probably what I'd use.

Technically you cannot strip out NM cable and use the conductors as they are not labelled individually even though they are THHN.
I think his load is likely to be a lot less than 15A. He didn't post what the full load amperage or minimum circuit ampacity is, but a quick search shows most 1.5 ton mini splits as drawing 6-10A at 240V. If his is in that range, #14 would be just fine and #12 is overkill.
 

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Romex should not be ran outdoors even in a conduit. You need THWN -2 for outdoors. The romex can be in a box or conduit body as soon as it penitrates the exterior and then be spliced to single conductor.
 

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Fuse size (time delay) (A) 15
What's time delay mean?
Fuses are either fast acting or time delay. The time delay fuses will hold a load much greater than their rating for a short duration of time. This allows a motor to come up to speed and settle down to its normal running amperage, before the over current protection at rating (15 amps in your case) is effective.

If you used the fast acting fuse of 15 amps, you might blow the fuse every time the motor started.

Because of the specified time delay fuse, I would use a 20 amp breaker with the 12/2, not the 15amp breaker you mentioned. The breaker will protect the wire at its rating, while the fuse protects the motor at its rating.
 

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Discussion Starter · #11 ·
Thanks SP for your input, helpful. What's UF cable? What Size? Second when a unit calls for a 15 amp breaker, I believe that's what you are suppose to use! Why would you put in a 20 amp breaker that wouldn't trip when it needs to? Still don't know what time delay means.
Knowledge is power....
 

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A "Handy Husband"
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UF-B cable is plastic jacket cable used in wet locations or direct burial. It is configured similar to NM-B. The size is the same as you would use for NM-B.
 

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A "Handy Husband"
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Never said anything about wet locations, what I asked was can Romex be run inside conduit for a couple of feet with out any issues ..
In post #5 you asked about running the same wire (NM) unsheathed in the whip to the unit. Conduit outside is a wet location.
 
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