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220V mini A/C wired as 110V

Posted by mikeinmayberry (My Page) on
Sun, Jun 20, 10 at 13:47

New here...I like what I've seen so far. I'm a jack of all trades, retired, working on a 2nd home I've recently purchased. This home, the money pit, is a 1-1/2 story with a full basement. The top room has a "mini-split" heat pump...darn thing wouldn't work. Upon further investigation I found the outside compressor was a 220V unit wired as a 110V. I called a local A/C outfit and they said I could remove the dedicated single 15A breaker, add a 15A 2 pole (30A) in its place. As the panel is 2 storys below in the basement, and all I have is 14/2 + bare grnd wiring, he suggested I hook the 2 pole breaker up with the black & white, and run the bare ground to the neutral bar. Now the A/C works (I do not need the heat pump to function). Everytime I leave this 2nd home, I shut the breaker off as I really have doughts this is correct. I haven't found a easy way to run a new 14/3 + grnd (or 14/4 if I want the heat pump to work) without tearing up a lot of sheetrock. An I over thinking this? I'd hate to burn the place down. Advice appriciated...Mike in Mayberry


Follow-Up Postings:

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RE: 220V mini A/C wired as 110V

As long as the apppliance you're powering doesn't have any 120v loads, and the bare ground is used only as an equipment ground (not as a return for 120v loads), there's nothing wrong with what you did for 240v on 14-2WG. You should re-identify the white wire at each end by wrapping it in black electrical tape.

I don't know why rewiring it that way would disable the heat ppump. Did it work before? Others here may have more ideas on that.

If it has a resistive backup heater, as many heat ppumps do, I'd be surprised if a 15a circuit would be enough to power that. Maybe if it is a very low output unit. IIRC, most of the splits I've seen have been 9,000 btu and up.

FYI, a 15 amp two-pole breaker is still 15 amps, not 30 amps.


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RE: 220V mini A/C wired as 110V

Thanks David. The compressor cooling fan in the outside unit is 220V. The inside unit fan is 110V...it was working when the unit was incorrectly wired, and works now. It is powered off of the 220V outside unit terminal strip...not a separate inside circuit. As for the 4th wire it would operate the reversing valve on the outside unit (no aux heat in this little system). From the breaker panel to the outside unit was wired as a 110V, I added the 2 pole breaker and now it works. The inside fan unit is powered via a 14/2 Romex from the outside unit when it should have used a factory fabricated cable that had the extra conductor to control the reversing valve.

Forgive me for being ignorant, but a 2 pole breaker marked 15A means each pole is only good for 7.5A? I was under the assumption each pole was good for 15A...I learn something every day.


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RE: 220V mini A/C wired as 110V

David...let me clarify my dbl pole confussion...I understand it's 240V/15A. I'm working on another project running power to the dock. I have a 100A sub-panel off of the main...a 100A 2 pole in the main is its supply. Inside the sub is a 40A 2 pole feeding my tram, a 30A 2 pole for future garage, and a 30A 2 pole going down to the dock. On the dock a sub-sub-panel fed by the 30A 240V has 1ea 10ga wire feeding each of the 2 breaker bars. On one bar I plan on 3ea 20A 120V single pole GFCI, the other side a single 20A 120V single pole as it's dock lighting only and the GFCI isn't req'd per the county mounty. In my simple mind the sub-sub-panel is 60A, but only as 120V service.


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RE: 220V mini A/C wired as 110V

A 30dp breaker gives 30A at 240V or two 30A at 120V if a neutral is present. Your subpanel at the dock is a 30A subpanel; hopefully it is fed by 4 wires, H-H-N-G.


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RE: 220V mini A/C wired as 110V

It sounds to me like you're saying the inside aircon unit is powered by the outside unit, which in turn is connected to a 240 volt source. If the inside unit requires 120 volts, you can NOT power it from the outside unit unless you have a 3-wire-with-ground cable to the outside unit.

The reason for this is that with a 2-wire cable you are using the groundING conductor for 120v power. This is not only a code violation, it's dangerous. In some cases where a fault exists in the house wiring, this can put line voltage on the cabinet or casing of a grounded device. This can be DEADLY.

If the inside unit needs 120 volts and that voltage is derived from the outside unit, you will have to rewire the outside unit with 14-3 or 12-3 cable, whichever is specified in the installation manual.

An alternative to rewiring is to use a 240:120 volt transformer to derive the power for the inside unit. The transformer will have to be sized for the load the inside unit presents.

The breaker rating is per pole. A double pole 30a breaker is still called a 30a breaker. It can supply 30a of 240v power, or two circuits' worth of 30a / 120v power. In any case its overprotection limit is always 30 amps. Hope this makes sense!


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RE: 220V mini A/C wired as 110V

I wrote some stuff on your other thread. Still need to confirm how you connected up the outside unit.

I'm going to guess that the outside unit requires two hots, a neutral and a ground. You connected two hots and a neutral but no ground. (The bare wire is connected to neutral at both ends.) This will work. Your unit will run happily. But both the inside and outside units are ungrounded. This is not safe, nor code (if you care). You should replace the 14/2 with 14/3 at your convenience. Run it on the outside of the house if you have to.

As for the heat, the required wire is a control wire, not a power-carrying wire per se. You don't have to run anything else from the box. You need to run a wire from the outdoor unit to the indoor unit. It probably doesn't need to be very large, like 16 ga, but it must be insulated.

BTW: since there is 14/2 between the outside unit and the inside unit, where is the bare wire from this cable connected? Ground or Neutral or not at all?


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