Mr. Cool 18k wiring double check
- Thread starter PCustoms
- Start date
That seems appropriate based on the ones I've installed and the chart. I assume it's a 240v setup, I guess you could think about going to 10/2 and a 25amp breaker if it's a 120v setup or if you want it to be a little safer. Make sure and install a surge protector at the outside disconnect, the control boards are really sensitive to spikes and will die fast without one.
Yes, 240v unit
Crazy that each manual lists different info. I think I really need the nameplate on the unit, but I can't seem to find that online.
mike93lx
ALLIANCE MEMBER
For an 18k, i'd do 12/2 and a 20a without another thought.
My cheap 2.5 ton heat pumps are on a 25...no really a wildly efficient 18k mini should need that
My cheap 2.5 ton heat pumps are on a 25...no really a wildly efficient 18k mini should need that
10/2 is nuts in coat right now, and I'm pretty sure I've got a roll of 12/2 already.
Max distance is like 50' if I come off the main panel. I guess I can get a 25A breaker. What throws me is I suspect this needs a fused disconnect but no mention in the install manual...
Max distance is like 50' if I come off the main panel. I guess I can get a 25A breaker. What throws me is I suspect this needs a fused disconnect but no mention in the install manual...
Despite searching earlier before starting a new thread, I didn't find this until now:
25A breaker with 12/2 NM-B
I think I know the answer already, but asking anyway. House was built in 2003, a/c systems are all original. I had previously noticed that my 1st and 2nd floor a/c systems (identical systems) used 10/2 nm-b and 25 a breakers. It caught my eye as it wasn't a 30a breaker but smaller is ok In...
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mike93lx
ALLIANCE MEMBER
That dude is a weirdo. I wouldn't listen to himDespite searching earlier before starting a new thread, I didn't find this until now:
25A breaker with 12/2 NM-B
I think I know the answer already, but asking anyway. House was built in 2003, a/c systems are all original. I had previously noticed that my 1st and 2nd floor a/c systems (identical systems) used 10/2 nm-b and 25 a breakers. It caught my eye as it wasn't a 30a breaker but smaller is ok In...
I am by no means an expert but have installed/helped install probably 20 mini splits in the last five years in ID and WA and we never have used a fused disconnect, I think the breaker covers you. 90% of these involved a permit and were inspected and OKed by electrical inspectors, for whatever that's worth. When I asked they said I could use a fused one but didn't have to on any modern equipment, something about built in protection that old equipment didn't have. Unfortunately this stuff seems to be based on your inspectors opinion a lot of the time. So if you are pulling a permit it might be worth a phone call before you buy everything.
My understanding is you can run a 25 amp breaker with 12/2 in an air conditioning circuit if you want, where normally it would have to be a 20 amp breaker on 12/2. I am not sure you need to based on that chart, but could. Again, I am not an expert, just play one on the weekends sometimes.
My understanding is you can run a 25 amp breaker with 12/2 in an air conditioning circuit if you want, where normally it would have to be a 20 amp breaker on 12/2. I am not sure you need to based on that chart, but could. Again, I am not an expert, just play one on the weekends sometimes.
The MCA in the chart is minimum circuit ampacity, that means the wire must be rated at or above that after any corrections for ambient temp or length are made.
MOP is max overcurrent protection, that's the max fuse or breaker size.
12-2 nmb meets the 18 amp minimum so it's good
20 amp breaker is above the 18 amp min and below the 25 max so good there as well.
In this case it's also compliant to have the 12-2 on a 25 amp breaker( at least in the USA).
Unless stated otherwise either fuse or breaker is fine.
Your plan of 12-2 on a 20 amp breaker is fine.
MOP is max overcurrent protection, that's the max fuse or breaker size.
12-2 nmb meets the 18 amp minimum so it's good
20 amp breaker is above the 18 amp min and below the 25 max so good there as well.
In this case it's also compliant to have the 12-2 on a 25 amp breaker( at least in the USA).
Unless stated otherwise either fuse or breaker is fine.
Your plan of 12-2 on a 20 amp breaker is fine.
I've got a funny feeling once the unit shows up it's going to say "max fuse 25A" on the unit.
Annoying that the manual and the unit don't match.
Certainly wouldn't surprise me, personally I would just use a fused disconnect anyway.
Every mini split manual I've seen feels like it's be translated though 5 or 6 languages before it made it to engrish.
Check my plan for wiring a Mr. Cool 18k unit, as I think I'm wrong/their chart *****:
12-2 NM-B
20A breaker
Non-fused disconnect
Well physical unit arrived and, surprise, is marked differently then the manual online.
- new manual calls for 15.5A MCA, MOP 25A
- My plan is still 12/2 on a 25A breaker
- unit is marked Max Fuse 25A
Question 2: is there a minimum height for the exterior disconnect? I'd like to exit the basement in a joist bay, which leaves the disconnect lower then I'd normally mount one. Other option (I see) is a interior junction box, thwn and an LB/conduit up the exterior, which is less then desirable.
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Raisedonadeere
Well-known member
I couldn't sort out all the information back when I did my first minisplit install. When all was ready and I still did not have a breaker, i put in a 15 amp that I had and it started running OK so I continued to shop for the correct breaker, I think i was shopping for "mythical" 25A but bought a 20 amp just to have something. That was over 5 years ago. The unit has run 24/7 with the 15A breaker through heating and cooling seasons in KY and the 15A breaker has never thrown so it is still there.
MadScientist3019
Active member
The interesting thing is to look at the LRA for the unit, I know on my 12k units the LRA for 240 is something like 8 amps. So why are they specifying such a large wiring/breaker size if the unit can't ever call for or cause more without damage?
A1: Different time curves between fuse and cb. Without spec'ing a fuse style, multiple fuses would fit the amapacity requirement but can vary drastically for the time curve. Any further details on the fuse requirement?
A2: No minimum but 36 - 48" is common.
From the basement, drill up into the stud bay through the sheathing/bottom plate. Fish cable up the wall and come into the back of the disconnect.