Wiring for Mini-Split

[whatuusay1]

I'm running power for my LG minisplit and I'm having second thoughts on the wiring. The manua shows it only needs 12G 2 conductor (and ground) wiring. so 12-2. I was thinking it would be prudent to run 12-3 in case it was ever needed (probably not by me but by someone in the future). I was also wondering if i should bump it up to 10-2(3) to be on the safe side.

Thoughts?

 

[Trey T]

If you believe the manual is inaccurate, check the full loading current (FLA) of the component(s). If it runs any more than 15A, then you might want to bump to a thicker Romex. Don't spend the extra $$ if you don't needed.

As far as having the extra wire(3+1ground) for neutral, it's up to you. I don't see why I would ever need it or any residential HVAC would call for but I could be mistaken.

 

[offroadsteve]

I second the check on the rated current draw of the component, but typically the installation instructions should be sufficent.

12 gauge is rated for a 20 amp load, and from what I have read you don't want to exceed 80% of the circuit rating for continuous use. So, if your current draw exceeds 16 amps, you need to go up in wire size.

Since you are wiring for a dedicated purpose, I don't see any value in spending the money on 12/3, unless you've just got a spool of it laying around. Ditto for going to 10 gauge without good cause... last time I priced wire the jump from 12 gauge to 10 was significant.

 

[whatuusay1]

Thanks guys - no i trust the manual, i just always like to exceep minimum spec

I dont see ever replacing the unit with one that would need the additional wire - just kicking around ideas. Its a dedicated line - and I'm following the manual's recommendation. They indicate a 12G 2 conductor (plus ground) wire for the main unit, 18G 3 wire (plus ground) for the inside unit. They also specify a 25A Breaker in the panel. Its a high efficiency unit (18 SEER). I dont anticipate it drawing high current.

 

[porcupine73]

Having 3/c (w/gnd) might give the flexibility to install a different unit in the future that might require say 240VAC with a neutral, but it wouldn't be of benefit right now. If the wiring run is quite a distance from the panel, going to 10 ga. might give you a little better efficiency, but might never be enough to pay for the extra cost of heavier gauge wire.

 

[porcupine73]

A 25A breaker? Are those commonly available? It seems they go like 15A, 20A, 30A, 40A, etc. I don't remember seeing 25A commonly at the hardware stores but I might have missed it. It wants the 12. ga wire to be fed from the 25A breaker?

eta...ah ok it looks like 25A breakers are available for most panels. The latest code I have is 2008, but in a table in the back it says 'unless otherwise specifically permitted elsewhere in this Code, the overcurrent protection for these conductor types shall not exceed ... 20 amperes for 12 AWG'.

 

[whatuusay1]

yea - it says 25A breaker - 30A Max. The run is probably 15-20ft max. I'm just going off the manual. Here's a link if anyone wants to make sure I'm not reading it wrong. Electrical is on page 20.

http://www.goductless.com/v/vspfiles/assets/images/pdf/lg/lg/lsn240hsv_install.pdf

Thanks,
Andrew

 

[offroadsteve]

Would figure the manual would be in metric... I suspect they spec a 25 amp CB or slow-blow fuse to make sure it doesn't nuisance trip on compressor start-up.

In that case I would use 10/2 for the feeder to the outside unit, 30 amp CB in the panel, and a no-fuse disconnect outside next to the unit (I believe that is required within sight of the unit). The "connecting cable" as they call it between the outside and inside units is a tough one. I hesitate to use normal 14/2 romex for that, since it calls for it to be bundled with the refrigerant lines, but I don't think your allowed to use SOOW cord in that type of application either (in wall, permentant installation).

10/2 would be sufficent for any future A/C outside unit, that is very standard (romex to the disconnect, THNN in waterproof conduit between disconnect and unit). I'll have to defer to someone smarter for the connecting cable to the inside unit.

 

[whatuusay1]

Well guys - I called LG Support...which wasn't actually all that helpful. The person I spoke with said either 12 or 10g would be fine... they recommended a 20A circuit breaker so that would essentially max out the 12g cabling.

I had planned on using 12-2 and then 14-3 romex between the 2 units but after the doubt here I think i'll bump it up to 10-2 between the panel and the compressor just to be on the safe side. The wall is open at the moment so swapping out a 25ft of 10-2 is pretty easy.. after the drywall is up, painted and insulated is another story. I'd also venture that any failure of the 12g would be 'eventful' to say the least. I'd like to avoid those kinds of events at my house. Thanks for everyone's comments.

 

[whatuusay1]

I picked up some 10-2 today from homedepot - they had a great deal on some unboxed wire (47' marked as 25')

Anyways - I went ahead and replaced the 12 guage wire with the 10g guage wire just to be on the safe side, It took about 10 minutes and $30 bucks, money well spent for the peace of mind.

 

[Norcal]

If romex (NM) was not being used, 12 AWG & a 30A breaker would be fine, rules for A/C units are different then for branch circuits, because NM cable is limited to the 60 degree ampacity of table 310.16 it's a bit more restrictive. Last A/C unit I connected it would have been allowed to use 14 AWG W/ A 30A circuit breaker.