220V Air Conditioner Mystery

criticalmass048May 30, 2010

About 12 years ago, we had two identical 220V wall air conditioners placed directly above one another, one on the 1st floor and one on the 2nd floor.

I tried to use the air conditioner on the 1st floor for the first time this season last night, and it didn't work.

I got out my multimeter, and tested the output. I got 70V AC out of the outlet. Just for good measure, I tested the outlet on the 2nd floor, and got 240V AC.

Thinking it might be the outlet, I bought a new receptacle, removed the old one, sandpapered the ends of the wires (they looked a bit dirty), and replaced it with a new one. Unfortunately, I'm still getting 70V.

The fact that the 2nd floor works fine leads me to believe that the breaker is not faulty.

The wiring was done through conduit running outside. There is an outdoor junction box outside the 1st floor outlet, presumably where they pigtailed wires together, one set to enter the 1st floor and one set to go up to 2nd. It's about 10 ft off the ground, so I can reach it with a ladder, but being that I have a fear of ladders, and it's right near my cellar steps, I thought I'd fish for opinions before I went up there. Six foot five, and I'm afraid of ladders. Can you believe it?

Thanks for the input.

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mike_kaiser_gw

Two 240v appliances on a single circuit? Sounds like a code issue to me. 240v appliances should be on a dedicated circuit. Assuming the circuits are wired properly, is it possible that you failed to notice the second breaker? It is quite possible and somewhat common for one of the two poles of a double pole breaker to trip without the fault making the breaker appear to be "tripped".

70v with a digital mulitimeter sounds like induced voltage, phantom voltage, whatever you want to call it. Use a solenoid type tester or put a load in the circuit and I'd bet the voltage drops to zero. A 240v volt circuit has two hots and a ground. You should get 240v hot to hot and 120v hot to ground. At the bad receptacle did you try hot to ground?

    Bookmark   May 30, 2010 at 6:00PM
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joed

It's a loose connection somewhere or there is another breaker that is turned off.

    Bookmark   May 30, 2010 at 7:36PM
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criticalmass048

As far as it being code, I'm not sure if it is or isn't. I never really even thought about it until now (never had a need to touch that breaker). But yes, they're on the same breaker.

As for one side tripping and the other not, that problem would have been fixed when I replaced the outlet -- breaker was turned off before work, and back on after the work was done.

Testing between one side and GND gave me 120V, but the other side and GND gave me about 9V. I guess I need to head out to that junction box and check on the status of that pigtail.

    Bookmark   May 30, 2010 at 10:08PM
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pharkus

Code-wise, I'm not sure. I've seen it done, several times (wood shops / mills with 240V tools and receptacles). I *believe* it's the same deal as 120V general receptacles: If it's a 15A or 20A circuit, you can have multiple devices on one.

Of course, given the region I live in, "I've seen it done" does not necessarily mean "it is legal".

Now, back to your problem. Yep. Up the ladder you go. Turn the breaker off first.

The side that gave you 9V is disconnected. Probably somebody didn't put a wire nut on tight enough or didn't make sure all three conductors went into it evenly, and one has worked its way out (or, worse, melted its way out)

    Bookmark   May 31, 2010 at 12:33AM
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petey_racer

"Two 240v appliances on a single circuit? Sounds like a code issue to me. 240v appliances should be on a dedicated circuit."

Seriously? Why?
I can tell you for a fact that it is allowed. How is this ANY different than having several 120v receptacles on a circuit???

    Bookmark   May 31, 2010 at 11:36AM
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mike_kaiser_gw

Petey,

I stand corrected...

    Bookmark   May 31, 2010 at 9:19PM
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brickeyee

The only issue would be if the manufacturer's installation instructions REQUIRE a seperate circuit.

If they only recommend a seperate circuit you are good to go.

    Bookmark   June 2, 2010 at 3:17PM
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criticalmass048

Well, it turns out I was wrong. I opened up the junction box outside, and there IS a separate cable going up to the 2nd floor. A quick trip to the basement showed that, yes, there are two cables going out through a hole in the wall.

The bad news is, that means there was no "loose wire nut" to fix. The problem is worse -- and more expensive. I made a nick in the black wire inside the box just to hook my tester up to it. Sure enough, it still wasn't getting power. So I went into the basement again, cut the cable, and tested the output there. Everything seems fine, meaning the "problem" area is somewhere inside the conduit.

I've purchased new 10 AWG wire to run from the cut point up to the box, and a new junction box so that I can splice the wires together. The only trick will be getting a second 10AWG wire out of the conduit, and another back in. If I could detach all the parts, I'm sure it would be easier, but remember, I already have another wire going through them up to the 2nd floor, so the conduit won't come apart. I'll just somehow have to get the thick wire around that 90 degree elbow.

    Bookmark   June 2, 2010 at 3:32PM
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spencer_electrician

Remember romex cable is not allowed in this installation, if that is what you bought (orange cable with 2 conductors/ ground. You have to use thwn conductors in the outdoor pipe and junction box to romex where it enter the house. Assuming you get stranded #10 thwn wires, it may not be too bad to maneuver through existing pipe. If the previous installer used romex cable in the pipe, it may have deteriorated causing your power loss problem.

    Bookmark   June 2, 2010 at 6:30PM
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pharkus

I believe Romex IS allowed in conduit you just have to derate accordingly for fill...

That doesn't make it a good idea though, nor any less of a PITA.

    Bookmark   June 2, 2010 at 8:41PM
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brickeyee

NM in conduit depends on what year NEC is in effect.

The articls got changed a few revs back so that the cable listing had to say it was allowed in conduit, and not all the cable listingas were updated at the same time.

NM is allowed in coduit for protection from damage, but that is NOT the same as installing it in a 'conduit system.'

The protection installation does not have to be complete, you can use short sections as needed.

    Bookmark   June 3, 2010 at 12:57PM
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spencer_electrician

I'm saying it can not be used outdoors period.

    Bookmark   June 3, 2010 at 10:56PM
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