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Old 10-24-2012, 07:50 PM   #1
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240V breaker - multimeter tests 120 V at junction box???


Please Help!! I will explain as much as I know about this circuit. The breaker was for radiant ceiling heat in one of my bedrooms which wasn't working. I figured the ceiling heat was the problem, not the electrical. The heating system is old, we just bought this house, and I installed a wall mounted 240V heating unit to replace the ceiling heat that didn't work. I found the junction box in the attic (for the ceiling heat) so I ran 10-3 wire from the unit to the junction box. The heating unit actually ran when I first installed it, now it does not. I tested the wires at the heater and I don't have any voltage between the black and white, but from the ground to black and ground to white gives me 120V. I went back to the attic and tested the wires in the junction box. (there are (2) wires coming into the box + the new 10-3 wire. I don't get any voltage from any black/white combination, and I get 120V from only one existing white wire to the ground......I have no idea what could be the problem, does anyone have any ideas on what could be going on? My double pole breaker tested 240V in my panel so I know thats good.
Thank you,


Last edited by bnadeau03; 10-24-2012 at 07:52 PM.
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Old 10-24-2012, 07:53 PM   #2
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240V breaker - multimeter tests 120 V at junction box???


Starting at the breaker panel...how do your wires run? What's connected to the breaker? Why did you run 3 wire cable?

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Old 10-24-2012, 07:54 PM   #3
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240V breaker - multimeter tests 120 V at junction box???


I'm guessing your splice in the attic is bad and you are reading voltage thru the heating element...which is giving you 120V to ground on each leg, but 0V between the black and white.
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