Electrical work to mini split

[panini]

I have two 27k BTU MRCOOL mini split that needs to be installed for my house. I am at SF bay area, CA.
I have two car attached garage which has subpanel and then there is main panel+meter base outside the wall.
I am pulling two 240v circuits, each on their own 40amp circuit breakers from the subpanel in garage.
First pull will be about 50ft from subpanel to first condenser disconnect and about 25ft from subpanel to second.
First condenser is on north of the house while second one is to the south. Subpanel in garage is closer to south condenser.

I plan to have sch80 pvc 3/4inch conduit from subpanel, then thru floor to the crawlspace and then to AC disconnect box.
I am planning to have 10-AWG THHN wires - Red and Black for hot and 12-AWG THHN Green for Ground.

Can I get away with 12-AWG THHN for ground or should I cough up for 10-AWG for Ground as well?
Also, given 500ft of 10-AWG cost less, can I reuse Red/Black as ground and tape/mark appropriately at panel and disconnect that its Ground?

CA is at 2022 NEC code, FWIW.

 

[Kezorm]

Ground needs to be 10AWG for 25-60 Amp. Needs to be green. Only 4AWG and larger can be re-identified. Also think you need 8AWG for 40A circuit.

 

[pcmeiners]

Just checked the installation manual, Kezorm is correct. Yes, I know no one likes thoroughly reading manuals but mini split are not cheap, you can not afford mistakes.

 

[panini]

I did read manual, for 27K, it does says 10AWG is fine as 40A is MOP while 26A is MCA.

 

[Kezorm]

If you protect with 30A breaker then 10AWG is fine. 40A (max allowed breaker for this equipment) requires 8AWG. 10AWG green ground either way.

 

[Kezorm]

I stand corrected. For this specific application (A/C compressor with MCA = 26A and MOP = 40A), 10AWG on 40A breaker is ok.

Ground still needs to be 10AWG green.

 

[panini]

Awesome, thank you Kezorm!

 

[Kezorm]

That said, you're only talking $30-40 difference between running minimum 10AWG or preferred 8AWG.

 

[panini]

The sparky that ran the electrical to ducted AC before I got this place has done a hacky job of running NM cable from subpanel -> crawlspace->AC disconnect. The NM cable, although in sheath, is just lying on the bare floor/earth. I have to get rid of it and then redo that as well with sch80 PVC conduit and THHN cable. So I am looking at close to 150ft of each color. Looking at price of 8 AWG THHN on Homedepot, it appears it costs pretty $$$ to get this done. Well, I agree I will buckle in for 8AWG THHN.

 

[mike93lx]

That said, you're only talking $30-40 difference between running minimum 10AWG or preferred 8AWG.

10 is plenty for a 2ton a/c assuming the run isn't super long.

 

[Jlanciani]

Why sch80 PVC? Sch40 is adequate and less expensive.

 

[panini]

Why sch80 PVC? Sch40 is adequate and less expensive.

Not for code for the fear of animals in crawlspace chewing thru. We have lot of squirrels around, there's a big pine in neighbor yard and that hosts bunch of other critters which I fear will one day make to my crawlspace and chew on these conduits. Haven't researched who stands better for these animals - sch40 ro sch80. I hope I won't be forced for EMT given its already costing pretty penny to go for 8AWG THHN.

 

[panini]

I stand corrected. For this specific application (A/C compressor with MCA = 26A and MOP = 40A), 10AWG on 40A breaker is ok.

Ground still needs to be 10AWG green.

Youtube auto suggested this after watching video you tagged, which provides better explaination:

 

[Kezorm]

Wire & Cable Your Way: Electrical Wire By the Foot

We are a trusted online distributor of electrical wire and cable products, offering fast shipping on a huge selection of SKUs, cut-by-the-foot or in bulk.

www.wireandcableyourway.com

150' of 2x 8AWG + 1x 10AWG = $225
150' of 3x 10AWG = $171

Note that you don't actually need different colors for the 2 hots.

 

[mike93lx]

Wire & Cable Your Way: Electrical Wire By the Foot

We are a trusted online distributor of electrical wire and cable products, offering fast shipping on a huge selection of SKUs, cut-by-the-foot or in bulk.

www.wireandcableyourway.com

150' of 2x 8AWG + 1x 10AWG = $225
150' of 3x 10AWG = $171

Note that you don't actually need different colors for the 2 hots.

How much is #6? If you are going to oversize unnecessarily, you might as well go full send?

 

[Kezorm]

How much is #6? If you are going to oversize unnecessarily, you might as well go full send?

Manufacturer stating that 8AWG is preferred doesn't mean anything? Never any reason to go beyond the absolute minimum required by code?

 

[mike93lx]

Manufacturer stating that 8AWG is preferred doesn't mean anything? Never any reason to go beyond the absolute minimum required by code?

To what gain? You can always throw more money at stuff.

#10 is not a compromise. It will work fine and #8 won't make it work better or last longer

They need to solve for lots of scenarios in their manuals. On a long run, yes #8 would be needed to compensate for voltage drop. It's no skin off their back if you spend more than is needed on wiring.