pre wiring for a mini split air conditioner

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  #1  
Old 04-02-06, 08:44 AM
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Arrow pre wiring for a mini split air conditioner

Hello,
we will be having installed a mini-split air conditioning unit (18,000 btus) in our home in the summer.

We are getting ready to hang the drywall in our basement and want to run the wire for the a/c unit (but not connect it) so that the a/c guy doesn't have to mess up our new drywall.

What type of wire should I buy and pull? It says on my quote for the mini split that there would be a 20amp breaker included, so I would assume awg 12, but should it be a 12-3 or 12-2?

It is an LG 18,000 btu art cool mini split.

thanks -jp
 
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  #2  
Old 04-02-06, 01:24 PM
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If it is a 120 volt unit, then you will need 12/2 w/g.

If it is 240, then you need more specific information from the manufacturer. Probably still just a 240 receptacle with ground but no neutral required, so still good with 12/2. The complete installation manual is probably available for download . Try www.lge.com or www.lgcommercial.com
 
  #3  
Old 04-02-06, 02:25 PM
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Originally Posted by jamiep
We ... want to run the wire for the a/c unit (but not connect it) so that the a/c guy doesn't have to mess up our new drywall.
If you run it, you connect.

The "A/C guy" is taking a risk if he connects to a cable that you ran.


> It says on my quote for the mini split that there would be a
> 20amp breaker included, so I would assume awg 12,
> but should it be a 12-3 or 12-2?

12-3. Uncalled for comment. You can make a statement without making people feel stupid..

You need to confirm with the "A/C guy" how he wants it done and exactly what cable he wants. We can't tell him what to accept. You do it his way or he can refuse to connect.
You should allow him to inspect the cable before you cover over it.

You could have the holes at the wrong place, physical damage, potential physical damage, bends too sharp, no allowance for linear contraction, inadequate fastening, insufficient slack at the boxes, etc.
 

Last edited by mattison; 04-03-06 at 04:40 AM.
  #4  
Old 04-02-06, 02:33 PM
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Originally Posted by 594tough
If it is a 120 volt unit, then you will need 12/2 w/g.
18,000 BTU would be more than 18A.


> If it is 240

It better be.


> you need more specific information from the manufacturer.

Or better yet, from the installer.


> Probably still just a 240 receptacle with ground but no neutral
> required, so still good with 12/2.

First of all, no neutral limits future possibilities for the circuit and will require ripping open the wall which is exactly what they want to avoid.
So right there, they should insist on a minimum of 12/3.

Secondly, what is the chance that no neutral is required?
Something this fancy probably has some 120V electronics. Regardless, someday it will be replaced. The next unit could require a neutral.
 
  #5  
Old 04-02-06, 06:20 PM
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Angry

I have found the manual online as per another user's suggestion. It says

Model: 18K BTU
Power Source 1Ø, 230/208v
AWG (min) º:14 ":18
Fuse or breaker capacity: 20A

Connection cable (low voltage): Use type SJO-WA

What does this mean? I understand 12 guage wire is fine, but what about the 230/208 thing?

thanks everybody else,
-jp
 

Last edited by jamiep; 04-04-06 at 08:39 PM.
  #6  
Old 04-02-06, 08:38 PM
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No crystal ball so I don't know if the run would permit but instead why not conduit (with a pull string) in the wall instead of wire. If lots of direction changes you could add pull boxes. Maybe a separate conduit for the low voltage cable.
 
  #7  
Old 04-02-06, 09:32 PM
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Originally Posted by jamiep
Thanks for your concern
You're welcome.

> this is a community where people ask for advice,
> not for some holier-than-thou know it all to tell people off.

I'm just telling you that you are asking the wrong people.
The only person who can answer the question is the person installing the unit.

It doesn't matter what we say. If he doesn't like it, wo aren't the ones who have to fix your wall.


> Power Source 1, 230/208v

That's single phase but you may use one leg (208V) of a three-phase system if that's what you have (e.g., commercial space or heavy-duty residential estate).


> what about the 230/208 thing?

Not to worry. What you have in your house is fine.
 
  #8  
Old 04-04-06, 08:38 PM
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> Power Source 1, 230/208v

That's single phase but you may use one leg (208V) of a three-phase system if that's what you have (e.g., commercial space or heavy-duty residential estate).

Perfect -- I think I am understanding this now. It's basically wired just like a dryer or range. So the breaker and wiring will actually be supplying 240 (2 x 120) but the a/c unit only will use 230 of it. The 12-3 wiring will be two hots, one neutral and one ground.

Is the neutral necessary, though? I read a short article and found this photo of inside an a/c disconnect box (link). It seems to be using 2 hots plus ground and no neutral.

Just to further my education, how would that work?

Here's the instruction link for reference

thanks -j
 
  #9  
Old 04-04-06, 09:21 PM
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normally most central A/C installment i dealt with it most use 10-2 wires but very few required 10-3 [ that pretty rare unless it is 3 phase that diffrent subject i will leave this out for now ]

some AC outdoor unit do have 120 volt system in there some case it might need netural wire for it but as i speak majorty of them are 240v volt for that size and larger.

the other thing i dont know if this is part of code or not but you need a 120 volt outlet withen 25 feet of ac outdoor unit it came up in 05 code cycle not too long ago. you may have to check with inspector and the HVAC contractor whom will install this unit they will have final say so with location and where they want to bring the freon pipes and other stuff as needed.

merci , marc
 
  #10  
Old 04-04-06, 09:52 PM
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Originally Posted by jamiep
It's basically wired just like a dryer or range.
I suppose you could say that.


> So the breaker and wiring will actually be supplying
> 240 (2 x 120)

Well, it's probably more like 2 x 125V.

> but the a/c unit only will use 230 of it.

No. The unit requires at least 195V or something like that.
But if you give it 252V, it uses 252V.

It uses only the amperage that it needs.


> The 12-3 wiring will be two hots, one neutral and one ground.

Correct.


> Is the neutral necessary, though?

On this specific unit it might not be.

> I read a short article and found this photo of inside an a/c disconnect box.
> It seems to be using 2 hots plus ground and no neutral.

That is an outdoor compressor.

> Just to further my education, how would that work?

Unlike a dryer or range, it has no 120V loads in it.

Your wall mounted unit probably has fancy controls.
It might require some 120V circuitry (as does a clothes dryer or range accessories).

Yours might might require 240/120V or 208Y/120V or it might not.

The thing is, if this unit doesn't use a neutral and you forego the neutral, then you are locked into using only no-neutral models in the future - or ripping out your walls to run the correct cable.

Having the neutral protects your investment in the cable from obsolescence and the finished walls from demolition.
 
  #11  
Old 04-05-06, 08:16 PM
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Today, most residences have 120/240 volt. That is not completely universal, and has not always been standard. A long time ago, 110/220 was common, and then 115/230. So the terms 110, 115, and 120 are pretty much used interchangably. Virtually all equipment is designed with tolerance to operate properly at any voltage in the range 110 to 120 ( or 220 to 240 ). We are only talking 10%.


To use an overly simple example, if a light bulb had a resistance of 240 ohms, and we ran it on 120 volts, it would draw 0.5 amps and consume 60 watts. If we actually ran that bulb on 110 volts, it would draw 0.458 amps, and consume 50.4 watts. The light would not be as bright.

The manufacturer could call this a 60 watt bulb, a 55 watt bulb ( based on 115 volts) or a 50 watt bulb. Any of these would be an acceptable label.
 
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