Wiring for A/C mini-split

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  #1  
Old 09-10-07, 11:49 PM
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Question Wiring for A/C mini-split

I need to run a new 240V/20A supply circuit from the panel through the attic eave to an exterior wall about 15' away for an A/C mini-split condenser. The supply needs a shut off.

I also need to run 3 circuits back from the condenser to 3 separate locations in the house for the 3 indoor air handlers which are each powered from the main unit. Each of these needs to be 4 #14 conductors (power, control, plus ground).

My question is what is the best way to make the transition from the interior to the exterior keeping in mind that the appropriate cables need to go to 4 different locations inside the attic. Can I put a junction box over a hole cut in the eave, the shut-off box at the condenser, and then run all the cables in a single piece of 3/4" EMT between the two boxes? I would likely use flex PVC to the different locations once inside the attic but can flex PVC also be used to the panel? I don't suppose I could use NM cable instead since half of it would be in the conduit...or can I?

Thanks
Rick
 
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Old 09-11-07, 03:58 AM
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Why are you running the power and control to the inside units? This is typically done by the HVAC guy along with the line sets.
Typically the only electrical requirements are to feed the outside units.
 
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Old 09-11-07, 09:10 AM
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Three AH"s implies three cooling zones,, with an evaparator coil in each AH . One condensing-section for 3 AH's suggests a very complicated arrangement of refrigerant lines. Could you please first describe how the refrigerant lines between the three AH's and the condensing section will be connected? And, structurally speaking, how will these lines routed ? --- over the attic, under the bottom floor, etc. ?
 
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Old 09-11-07, 09:13 AM
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Uh, because the HVAC guys want $6000 (labor only) and I'm not willing to spend that. Plus, they said they won't do the electrical.
 
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Old 09-11-07, 09:24 AM
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Originally Posted by PATTBAA View Post
Three AH"s implies three cooling zones,, with an evaparator coil in each AH . One condensing-section for 3 AH's suggests a very complicated arrangement of refrigerant lines. Could you please first describe how the refrigerant lines between the three AH's and the condensing section will be connected? And, structurally speaking, how will these lines routed ? --- over the attic, under the bottom floor, etc. ?
Like I said in my original post, this is a multi-zone mini-split. Each indoor unit has it's own line set and receives power from the condenser (look up Fujitsu, Sanyo, or Mitsubishi mini-splits). The pre-cut, pre-flared linesets will be run in the attic...but my question is only about the wiring.
 
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Old 09-11-07, 10:41 AM
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Originally Posted by rickalders View Post
Uh, because the HVAC guys want $6000 (labor only) and I'm not willing to spend that. Plus, they said they won't do the electrical.
sorry to be rude in here but why that HVAC guy want to quote that much money for 3 runs of the lines to the air handler and hook up the unit ??

I am not sure where you are located so i dont know if that is a justifyable price with that much.

what about other HVAC contractors can they give you the estamate for those ??


If i recalled if i rember it right we did have someone else here did discussed about the split unit here but maybe i am wrong on this part the air handler on those type of unit is either 120volts or 24 volts for inside airhandlers and main power feed is the outside unit.

is the outside unit just one and it serve three indoor units ??

Thanks

Merci, Marc
 
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Old 09-11-07, 10:54 AM
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Any wire outside (even inside conduit) must be rated for wet conditions (THWN). i'm a bit confused as to which wires are going where, and what's outside... but how about this for an idea. I would use a junction box in the attic that goes outside via PVC conduit, then down the wall to the disconnect box, then a flexible liquid-tight conduit whip to the unit. Inside, the handlers would each have 14/4 (I think it exists) or THHN in PVC to the inside air handlers. You could use UF wire to go outside, but it gets complex with the outgoing and incoming wires - and it would seem that a single conduit with a junction box makes the most sense.

Good luck!
 
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Old 09-11-07, 10:56 AM
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Punch a 3/4 " knock-out in the bottom of the enclosure when the control terminations are located

using a THREADED ( metal ) 3/4 " LB fitting , "nipple" the LB to the KO with 2 locknut and a bushing --- set the LB so that the cover is parallel to the ground.

using 3'4 " PVC conduit, run the PVC horizontally from the LB to the wall ,wth an elbow at the wall-end that makes a 90 degree horizontal-to-vertical bend in the run.

Entend the 3/4 PVC vertically up the wall and thru a hole in the eave

If the slope of the rafters is 30 degrees , then bend the PVC so it confroms to the slope of the rafters- you MAY be able to use a 45 degree factory-made bend. The objective is to have the PVC terminate on a "deep" 4-11/16" outlet-box , fastened either to the side of a rafter , or under a cleat.

Pull the required #14 "zone" wires and ONE Green Equiptment Grounding Conductor thru the PVC. Extend from the "splice-box" to the individual AH's with 14/3 NM cable.

Run a 14/3 NM cable from the panel to the "splice-box" for providing a EGC from the panel which connects to the EGC's in the splice-box and bonds to the metal box. You can later use Black and White wires for , say, a ventilating fan.

For the 220 wire to the condensing section , run 12/2 ? NM cable from the panel and thru a hole in the eave and then thru a "sleeve" of 3'4 " PVC to the dis-connect switch. Note there are 2 EGC's at the termination - one in each run of PVC
 
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Old 09-11-07, 03:11 PM
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Non-metallic Type NM-B cable cannot be run outside even if in conduit. You would be better to run THWN conductors.
 
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Old 09-12-07, 07:57 AM
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HVAC guys are not crazy about installing systems they did not sell to you. You buy the system from a discounter, so he doesn't make a markup on it, and then you expect him to cover the labor on any warranty work later. You are lucky if you find anyone to do it at all.

These "mini-splits" are the latest gizmo. The outdoor condensors are designed as single, dual, or even triple zone. They have appropriate connections for the line sets which run to the indoor units. The control and power to the indoor units is often low voltage, sometimes 34 VDC. I don't know code-wise where this falls. But typically, I have seen the AC guy run that cable with the line set.
 
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Old 09-12-07, 10:04 AM
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Originally Posted by 594tough View Post
HVAC guys are not crazy about installing systems they did not sell to you. You buy the system from a discounter, so he doesn't make a markup on it, and then you expect him to cover the labor on any warranty work later. You are lucky if you find anyone to do it at all.
I'm doing the install, I'm only going to pay the HVAC guy to charge the system. Obviously, if he screws up vaccuuming it down or releasing the pre-charged refrigerant I'll hold him accountable but I wouldn't expect anyone to warranty labor on something they didn't install.

Originally Posted by 594tough View Post
These "mini-splits" are the latest gizmo. The outdoor condensors are designed as single, dual, or even triple zone. They have appropriate connections for the line sets which run to the indoor units. The control and power to the indoor units is often low voltage, sometimes 34 VDC. I don't know code-wise where this falls. But typically, I have seen the AC guy run that cable with the line set.
Actually they have been around for quite some time and are quieter and more efficient that traditional systems (up to 21 seer). They are offered in single to 4 zone commonly with even larger systems for large residential, multi-family, or commercial applications. The power to the indoor units on what I'm looking at is 220V. I wish they were low voltage, that would save quite a bit of work.
 
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