What size breaker for this?

[ybnormal70]

This is the rating listed on the outdoor unit of my new mini-split AC/Heat pump. It lists a minimum circuit ampacity of 18a and a max breaker of 25a. Would a 20a breaker suffice on this with 12ga THHN wire? One would be ran about 15' and the other about 30'.

Just kind of hoping I don't have to jump up to 25a breaker and buy 10ga THHN wire when I already have the 12ga THHN.

Thanks!

Kevin

 

[wyliesdiesels]

If you use #12 THWN in pipe then it will be ok as its rated for 25a (75* c column).

If using NM-b, then need #10.

Yes you need a 25a breaker.

EDIT: MCA is 18a not 25a. I misread the nameplate. So #12 NM-b is permitted as well.

 

[ybnormal70]

It would be #12 THHN in conduit. So the #12 is fine in conduit with the 25a breaker?

I just searched and found this table listed for #12 THHN:
Allowable Ampacity: 20 Amps at 60ºC / 20 Amps at 75ºC / 20 Amps at 90ºC

Would that be because it's not listing it in conduit?

Thanks.

Kevin

 

[Norcal]

It would be #12 THHN in conduit. So the #12 is fine in conduit with the 25a breaker?

I just searched and found this table listed for #12 THHN:
Allowable Ampacity: 20 Amps at 60ºC / 20 Amps at 75ºC / 20 Amps at 90ºC

Would that be because it's not listing it in conduit?

Thanks.

Kevin

With a A/C application 12 AWG THWN is a 25A conductor.

 

[05wrangler]

Will it run more than 3 hrs?

 

[Norcal]

Will it run more than 3 hrs?

Does not matter the 125% is already built in.

 

[brewchief]

In this situation #12 nm-b would be legal on a 25 amp breaker.

Sent from my XT1254 using Tapatalk

 

[Stuff]

In this situation #12 nm-b would be legal on a 25 amp breaker.

Even 14 gauge NM would be allowed by NEC. Inspector might argue.

 

[Norcal]

Even 14 gauge NM would be allowed by NEC. Inspector might argue.

14 AWG THWN, yes but not 14/2 NM.

 

[alfredeneuman]

NM is limited to the 60 degree column as far as the ampacity

 

[MattT]

Yes you need a 25a breaker.

I don't see why that mini needs a 25A breaker. Doubt it'll ever pull more than 15A under normal operation. Might pull a little more on initial power up depending on how well the bus charging is regulated.

 

[wyliesdiesels]

It would be #12 THHN in conduit. So the #12 is fine in conduit with the 25a breaker?

I just searched and found this table listed for #12 THHN:
Allowable Ampacity: 20 Amps at 60ºC / 20 Amps at 75ºC / 20 Amps at 90ºC

Would that be because it's not listing it in conduit?

Thanks.

Kevin

What table is that?

Should be looking at T310.15(B)(16)

Even 14 gauge NM would be allowed by NEC. Inspector might argue.

Nope.

Min circuit ampacity is 18a.

#12 NM is 20a so that is fine.
#14 NM is 15a so not permitted.

I don't see why that mini needs a 25A breaker. Doubt it'll ever pull more than 15A under normal operation. Might pull a little more on initial power up depending on how well the bus charging is regulated.

Because the manufacturer/nameplate calls for it.

 

[Stuff]

What table is that?

Should be looking at T310.15(B)(16)



Nope.

Min circuit ampacity is 18a.

#12 NM is 20a so that is fine.
#14 NM is 15a so not permitted.



Because the manufacturer/nameplate calls for it.

We are still on 2008 here so Table 310.16 shows #14 is 20 amps and #14 is 25 amps in 60º column. I keep on forgetting that the rest of the world has moved on.

 

[alfredeneuman]

The OP is on the 2014 NEC 15Amp in the 60 column

"#14 is 25 amps in 60º column"
Look again. It's 25 in the 90 column

NM is always rated at the 60 degree temp.

 

[chew]

Electrician here. It's Minimum Circuit Ampacity 18A and Maximum Fuse/Breaker 25A. So your fine with a 20A circuit. It's not saying 25A is recommended. The 25A just allows you to go that large if you had too and still trip under fault / overload conditions with out a fire and light show.

EDIT: I'll also add with #14 #12 and #10 having ampacitys higher then 15A, 20A and 30A is only typically used for derating in conduit. Because the code also states that unless other wise noted AWG #14, #12 and #10 shall not have over-current protection larger then 15A, 20A and 30A

 

[alfredeneuman]

Electrician here.
EDIT:. Because the code also states that unless other wise noted AWG #14, #12 and #10 shall not have over-current protection larger then 15A, 20A and 30A

"unless otherwise noted"
Those amperages do not apply to motors, welders, or AIR CONDITIONERS

 

[ybnormal70]

I think I understand now. Thanks everyone.

Kevin

 

[sberry]

I tend to agree, says max breaker. It is a standard practice to use that.