Rough wiring for mini-split

[bottom feeder]

I'm at the rough wiring stage in my detached garage. I"m planning to add a mini-split air conditioner/heat pump later on, and I'd like to run the wire for it while the walls are still opened up. I haven't made a final selection for make and model yet, but the following stats are for what would probably be the largest one I would potentially be using (one outside unit servicing one head unit inside the garage):

Electrical .......................... 208/230 V AC 1ph-60HZ
Available Voltage Range.............. 187 - 253 V +/- 10%
Max Fuse Size........................ 30 A
Max Operating Current (Evaporator)... 15.5 A
Max Starting Current (Condenser)..... 10.5 A

Input Power:
Cooling.............................. 1.76 kW
Heating.............................. 1.94 kW

Running Current:
Cooling.............................. 7.9 A
Heating.............................. 8.6 A

Capacity:
Compressor........................... Rotary x1
Motor Output......................... 2,100 W

Fan Motor
Type: DC (condenser)................. Propeller x1
Type: DC (evaporator)................ Cross flow fan x1
Motor Output (condenser)............. 100 W
Motor Output (evaporator)............ 53 W

Would 12 gauge copper (12/2 NM-B) be proper for this application, or should I use something larger, such as 10 gauge? The length from the breaker panel to the outside unit disconnect would be 25 feet.

Thank you!

 

[tab2]

10 gauge for 30 amp. From memory you need a decent sized unit to bump up from 30 amp. Breakers protect the wire and as far as I know there is no rule about having wire too big but the electrical code gurus will know better and respond accordingly.

 

[wyliesdiesels]

What is the MCA/minimum circuit amps as listed on the nameplate?

Wire is sized by the MCA and the fuse is sized by the MOCP- in your case 30a.

 

[MattT]

I haven't made a final selection for make and model yet, but the following stats are for what would probably be the largest one I would potentially be using (one outside unit servicing one head unit inside the garage)

Since you don't know what the unit requires run #10 just to be sure. And unless you're already planning to put a 120v receptacle outside near the condenser run a circuit for that too. Makes the install, and future servicing, easier and I think it's also a code requirement now.

 

[rlitman]

The 120V outlet is a code requirement now.

The disconnect will fit the 10 AWG just fine, so you won’t have any reason to regret going oversized if it isn’t needed.

 

[Norcal]

12 AWG with a 30A breaker is code compliant. If it was piped and THWN conductors were used 14 AWG would be OK.

 

[brewchief]

Without a minimum circuit ampacity listed clearly I would run 10 gauge for this unit, since it lists max fuse size and not max fuse/breaker size I would use a 30 amp fused disconnect.

Sent from my SM-G965U using Tapatalk

 

[dcg9381]

What is the MCA/minimum circuit amps as listed on the nameplate?

Wire is sized by the MCA and the fuse is sized by the MOCP- in your case 30a.

As usual, he's right.

Can you tell us what unit this is?
I've got 2 ton units (24k BTU) and manual say max fuse is 20A.

My 24k units pull less than 12A running, whatever that is worth. 10 ga wire would run some pretty big ones.

I "prefer" to stick with the wire matching the maximum breaker in case I re-use it for something later. That is, if I was expecting a 30A breaker, I'd wire with 10ga, but NorCal is also right that 30A on 12ga is totally code compliant in some cases.

Disconnect boxes - pay attention. Some are fused disconnects. Double the price of the "box" if you have to add fuses.

 

[fitter30]

Four wires are needed from condenser to indoor unit. Have to be run separate from power and no spices 14 gauge. Can use flex plastic conduit with a adaptor to sealtite to unit or if your code allows
https://www.ebay.com/itm/Honeywell-...4541970344c5e8af31337214a52de&redirect=mobile

 

[rlitman]

Four wires are needed from condenser to indoor unit. Have to be run separate from power and no spices 14 gauge. Can use flex plastic conduit with a adaptor to sealtite to unit or if your code allows
https://www.ebay.com/itm/Honeywell-...4541970344c5e8af31337214a52de&redirect=mobile

Yes, but that's not part of the pre-wiring he wants to do. That's going to get run with the refrigerant lineset at the time of the install.

 

[bottom feeder]

Thank you all for the replies!

What is the MCA/minimum circuit amps as listed on the nameplate?

Wire is sized by the MCA and the fuse is sized by the MOCP- in your case 30a.

As usual, he's right.

Can you tell us what unit this is?
I've got 2 ton units (24k BTU) and manual say max fuse is 20A.

The specs I used in my original post were for a Fujitsu 18RLXFWH, taken from a PDF on their web page. The specs didn't mention a MCA rating, so I did some more searching today and found a more comprehensive spec sheet that actually contradicts many of the specs on the first sheet. So either Fujitsu has revised the unit or corrected the specs, or both. This one has an MCA listed as 17 and a maximum circuit breaker size of 20A (on page 2):

https://portal.fujitsugeneral.com/files/catalog/files/18RLXFWH-2019B.pdf

Since I've been using Southwire brand NM-B wire, I looked up their chart to see what the various ampacity ratings are:

https://hvac.southwire.com/wp-content/uploads/2017/03/ROMEX-%C2%AE-SIMPULL-%C2%AE-TYPE-NM-B.pdf

They list the allowable ampacity of 12/2 copper romex at 20 A, so it would seem that 12/2 would be acceptable. However, since I don't know if this is the actual mini-split that I'm going to buy I think I'll go ahead and run 10/2 since the cost difference is fairly trivial.

 

[inphx]

Yes, but that's not part of the pre-wiring he wants to do. That's going to get run with the refrigerant lineset at the time of the install.

But if you do not at this time (with walls open) account for the 4 wire control wire routing , the refrigerant tubing lineset in the walls and the condensate drain lines... the OP needs to say hes got it covered otherwise it's an expensive oversight.

Also code may say you need to gave a 110v outlet nearby the condenser outside.. may as well run that now too.