# T-stat wire to feed air handler?



## CFL (Jan 28, 2009)

I've been waiting a few weeks for ac guy to install 2 mini split air conditioners. Each outside condenser feeds 2 inside units. I went by today to connect the condensing units and find that he ran 18awg tstat wire to inside. Unless I'm missing something, the inside units are 240v. The wire is not in conduit and it's buried in dirt when it exits the building down to the units. The units are LG artcool, and he told me 240v to condensers.

I'm going to look at them tomorrow (couldn't today) but has anyone wired this model? I'm pretty sure he screwed up but would like to know ahead of time if I'm mistaken. 

One of these wires isn't even long enough and I know he's not going to set a box to make a splice.

I know some models are low volt dc inside, but from what I could tell from different websites, all models fed with 240v have 240v air handlers.


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## cdnelectrician (Mar 14, 2008)

I see that a lot too...I am also curious to know what voltage these things run at. It's always hard to find the right cable to use for those split units. I have used PG cable in NMFC before.


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## Sparkyand1 (Aug 9, 2011)

I would say the thermostat wire is just communicating with the units, while your 240 volt circuit is what powers it up. Thermostat wire doesn't have to be ran in pipe because it's not carrying high voltage, it's about like telephone wire.


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## Shockdoc (Mar 4, 2010)

I've been told by Mechanical contractors that the condensate unit runs on dc current and they want nothing larger than a 14/3 run to it from the outside compressor even though that might be fused a 30 amperes . My question is what overcurrent protection if any exist for the wiring going out to the condensate unit(s).


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## jhall.sparky (Jun 14, 2011)

CFL said:


> I've been waiting a few weeks for ac guy to install 2 mini split air conditioners. Each outside condenser feeds 2 inside units. I went by today to connect the condensing units and find that he ran 18awg tstat wire to inside. Unless I'm missing something, the inside units are 240v. The wire is not in conduit and it's buried in dirt when it exits the building down to the units. The units are LG artcool, and he told me 240v to condensers.
> 
> I'm going to look at them tomorrow (couldn't today) but has anyone wired this model? I'm pretty sure he screwed up but would like to know ahead of time if I'm mistaken.
> 
> ...


http://us.lge.com/download/product/file/1000004106/Installation%20Manual_LA185HV_MFL39817303.pdf
here is the info you need what concerns the power starts on page 20.

those lg art cool are pretty cool , usually they come with an "ambilical" cord/ plug n play harness. id have to have the model number and ser number to get you the proper install procedures, however i do and always will run the lv-wiring in conduit ( seal-tite or something similar at the least) because weedeaters, animals and people always find ways to damage the wiring!

:thumbsup:


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## Dennis Alwon (May 9, 2009)

Many of the split systems today have a 24V DC motor in the inside unit. Obviously if there is heat back up then that sysytem would not work.


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## jhall.sparky (Jun 14, 2011)

Dennis Alwon said:


> Many of the split systems today have a 24V DC motor in the inside unit. Obviously if there is heat back up then that sysytem would not work.


i havent seen a mini-split yet that has ELECTRIC RESISTANCE heat in it.

208/230 vac is hooked up outside at the condenser, and then board rectified 24vdc is sent through to the id unit. it is a basic 18awg/4conducter hook up. 
2 call out, 1 reversal valve call, and 1 common.

these units are usually 8-12000 btu outputs.

a 18/4 tstat cable is the norm.


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## khfiei (Aug 20, 2011)

*ductless split system wiring*

We have been installing this equipment for years and the wiring requirements have evolved. Older equipment required separate power to the outdoor (compressor) unit and the indoor (evaporator) unit(s), and had a low-voltage thermostat wire interconnecting the units. Present (last 5 years) residential equipment (Mitsubishi, Fujitsu, Sanyo, etc.) require 220-volt power to the outdoor unit, which is fed through the unit to a terminal block for powering the indoor unit (or units depending on the number of indoor zones for the equipment) . A third wire is used for control and a fourth wire required for grounding (for each indoor unit). The power for each indoor unit is about 100-watts at 220 volts (mainly for the fan motor), and the control wire is about 12 volts, referenced to one of the power legs. For equipment up to 36k Btu, overcurrent protection is 20 amps, and a single, internal fuse, 30-amp, is connected between the compressor power and the terminal block powering the indoor units. 
As the three power/control wires are all over 100-volts to ground, and basically protected by the 20-amp overcurrent breaker, significant hazard exists if a proper wiring method is not used. We are NYC electricians and have had issues with the wiring methods used by others.
Most HVAC contractors run the power/control wiring between the units together with the refrigeration runs (we only provide the main power). To make it easy and cost effective, they have used flexible cords, (14-4 type SO, etc.), for the inter-unit wiring. I have seen a case where the contractor used 16-4 shielded stat wire for this application, and we had to replace it because it got damaged about a year after it was installed (at great expense because the interior walls were all finished).


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## khfiei (Aug 20, 2011)

*ductless split system wiring*

Further to our previous post, when we provide the interconnect wiring between the outdoor and indoor units, we usually run the exterior portion of the wiring (we use 4-#14 THHN stranded) in PVC conduit enclosed in PVC tracking (which the HVAC contractor installs to enclose the refrigeration tubing to make it pretty). We transition the PVC to Liquid-tight to the compressor. Once inside the building, we transition to FMC to the indoor unit. The indoor unit wiring compartments are usually small and the terminal blocks small, making it almost impossible to use anything other than 14 stranded. 
In July, 2011, NYC adapted the 2008 (yes, 2008) code, with a separate book of amendments, which permits the use of "multiconductor cable" (article 225.10) on the exterior of buildings. The amendments also restricted our use of PVC conduit for this application. I could not find in the 2008 code what this material or article describes it or its use. Any help?


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## CFL (Jan 28, 2009)

jhall.sparky said:


> i havent seen a mini-split yet that has ELECTRIC RESISTANCE heat in it.
> 
> 208/230 vac is hooked up outside at the condenser, and then board rectified 24vdc is sent through to the id unit. it is a basic 18awg/4conducter hook up.
> 2 call out, 1 reversal valve call, and 1 common.
> ...


I went back to look at those units and they are 240v inside and out. I told the ac guy he needs to use a different wiring method and 3 weeks later he finally had them done. He ended up running a cable made by Honeywell that they market as mini split cable. It's 14ga, 4 cond., 600V, tray cable.
At least he sleaved the cable in PVC outside. In the future I will insist on doing all of the electric.


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## robnj772 (Jan 15, 2008)

CFL said:


> I went back to look at those units and they are 240v inside and out. I told the ac guy he needs to use a different wiring method and 3 weeks later he finally had them done. He ended up running a cable made by Honeywell that they market as mini split cable. It's 14ga, 4 cond., 600V, tray cable.
> At least he sleaved the cable in PVC outside. In the future I will insist on doing all of the electric.


Yea 14 wire is the norm here. I put a tester on it and all the ones I have seen have line voltage on that wire.
Maybe we are talking a different type of unit.

Sent from my iPad using ET Forum


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## wcord (Jan 23, 2011)

There is the type which uses a 4 conductor low voltage as the interconnecting cable.
There is also the type which uses line voltage with a 3rd communication wire ( ie 14/3 or 12/3 )
Personally, I haven't encountered a unit which uses both voltages.


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