Mini split wire size - prewire thoughts

[jpcjguy]

Hi all,

So I am getting close to doing insulation and drywall and was thinking of running a couple wires into my attic area of the garage for future mini-splits. That way I don't have to fish wire down to the panel later. Just have them terminate in a junction box.
Garage is 48x30 so thinking maybe 2 for downstairs and 1 for upstairs?
What wire size should I run? This would be a short run of 6 feet or so.
Pics of the garage and interior space attached.

 

[tyme2par4]

Most of the residential sized mini-splits are going to require 12/2, some of the larger ones 10/2.
I've installed both an 18kBTU and 24BTU unit, and both required 12/2 wire.

 

[jpcjguy]

Most of the residential sized mini-splits are going to require 12/2, some of the larger ones 10/2.
I've installed both an 18kBTU and 24BTU unit, and both required 12/2 wire.

Thanks for the info - so running some 10/2 should cover me, unless I went with a 36k unit which takes 8 gauge!

I looked up the Mr Cool units on Ingrams site, iwae.com, and saw the attached chart in one of the install PDFs

 

[vtjon]

There is some discussion about if the PDF manual is wrong about the 36K unit. I have been going through this same discussion as I've prewired for a 36K unit. It is my understanding that the nameplate on the 36K says 25A so 10/2 on a 30A breaker is correct. There is some discussion in this very long thread:
https://www.garagejournal.com/forum/showthread.php?t=330969

I hope to order my 36K in a few weeks so I'll try to remember to report back. I have already pulled 10/2 in a 60A disconnect in hopes that it is correct.

 

[wyliesdiesels]

There is some discussion about if the PDF manual is wrong about the 36K unit. I have been going through this same discussion as I've prewired for a 36K unit. It is my understanding that the nameplate on the 36K says 25A so 10/2 on a 30A breaker is correct. There is some discussion in this very long thread:
https://www.garagejournal.com/forum/showthread.php?t=330969

I hope to order my 36K in a few weeks so I'll try to remember to report back. I have already pulled 10/2 in a 60A disconnect in hopes that it is correct.

Wire is sized by MCA listed on nameplate and breaker is sized by MOCP listed on nameplate.

#12 THWN is good for 25a but if you're gonna use NM-b then you need #10.

Also, make sure you don't need a neutral to run the air handler.

 

[dcg9381]

I have 24K units. They required 12/2, but run very comfortably under 15A (even at start up). More like 10-11A continuous.

When I started installing these things, I pre-wired for 10/3 - but it's total overkill unless you're going over 24k. You don't need the neutral anyway.

The way I've done it on my new home - I ran 10/3 to a centrally located sub-panel outside the garage. If I do a ductless system, I'll just split off that sub-panel... In your case, if you're thinking about 2-3 systems, I'd probably run 8/3 to an exterior panel.

 

[u2slow]

I'd run a 3/4 or 1" conduit to a large JB and leave it empty. Pull in what you need later.

 

[dcg9381]

I used 3/4 PVC conduit for drains.. Might pre-run those while you're in there.

 

[jeepxj]

just put in some conduit runs and leave them empty. also consider putting linesets in the wall.

 

[dcg9381]

I found that the linesets went through 2" Electrical PVC reasonably well. Makes the install a lot cleaner than going straight out and having to cover the lineset as it drops down the wall.

 

[mobetta]

the main service wiring needs to go to the compressors outside.

then a 14-3 or similar signal wire is generally run with the lineset
dont forget condensate drains

best is to get the equipment before the walls get sealed up

some kits come with everything included

My HVAC guy cut the cheap brass nuts off the linesets and installed new ones. They've had issues with them cracking.

 

[dcg9381]

the main service wiring needs to go to the compressors outside.
then a 14-3 or similar signal wire is generally run with the lineset
dont forget condensate drains

You can run 24K BTU ductless units that are 240V on 12/2 no problem. Check your particular specs to be sure. 10/2 is overkill but would power a bigger unit above 24k.

If you're going to run more than one ductless until, consider throwing up a 30A or 50A fed sub-panel outside centrally located.

Signal wire is, in my experience, 14-4, they make wire for this that is UV stable.

 

[ezzzzzzz]

I run two 24k units off the 36k inverter. The inverter is fed with 10/2. It's a Daikin unit and more than enough amperage capacity.

 

[jpcjguy]

Thanks for all the feedback. I have some 10/2 that I can use. Just also wanted to confirm I don't need 10/3.

 

[alfredeneuman]

Don't forget that a 120V outlet within 25' of the compressor is required for servicing the unit.

 

[dcg9381]

On the Daikins, you don't need 10/3, you can use 10/2. It'd help knowing exactly what you're going to put in.

alfredneuman is also right, a 120V service outlet is also necessary as well as a disconnect.

One way I've done this before is drop a Siemens Talon sub-panel outside, which has the 120V GFCI in it. Breakers in a sub panel that are easily accessible count as disconnects. Might be overkill for a single ductless - but it's $150 for everything you need - takes away the need for the disconnect and 120V separate.

 

[vtjon]

I finally purchased my 36k MrCool DIY system. As previously discussed, the nameplate does say 25A. I have attached a picture of the nameplate to help others in the future. I did pre-wire 10/2 so hopefully I'll be all set!

 

[dcg9381]

I have 24K units. They required 12/2, but run very comfortably under 15A (even at start up). More like 10-11A continuous.
.

I have 24k units.. I ran one on 12/2 and one on 10/2 pre-wires. I'll 2nd the experience above, both of mine ran fine on 15A breakers - but I eventually got the right spec 20A breaker on there.

If you don't know what you're going to do, I'd run 10/2.. But as noted, the vast majority to 24k run on 12/2 just fine.

I'd recommend doing some blocking for the mounts, setting the drain now. I actually ran my coolant lines through electrical conduit on the inside of the walls versus cut through to outside and have a cover over the coolant lines.

 

[wyliesdiesels]

I finally purchased my 36k MrCool DIY system. As previously discussed, the nameplate does say 25A. I have attached a picture of the nameplate to help others in the future. I did pre-wire 10/2 so hopefully I'll be all set!

Note that the nameplate says fuse, as opposed to breaker or fuse, or OCPD, so you need to use 40a fuses ONLY in a fusible disconnect.