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Old 04-05-2011, 12:13 AM   #1
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low voltage reading at receptacle

A friend of mine asked me to help him replace a GFCI duplex receptacle in his 2nd floor bathroom. Before I did anything, I checked the voltage readings by placing my meter probes into the slots of the receptacle. The reading for the upper slots read 17 vac and the bottom slots also 17 vac. Carefully, I pulled the receptacle out from the 2" x 4" plastic box and checked the voltage at the screws of the duplex receptacle; it read 34 vac. Since the door panel index to the circuit panel in the basement is not labeled for anyone to readily determine which breaker serves any of the branch circuits, through the process of elimination, I turned one breaker off at a time to figure out which breaker served the duplex receptacle in the bathroom I was working on. It turned out to be a double pole 50 amp 220 vac breaker. I checked the breaker at each pole to verify if the breaker itself was defective or not. Each pole read 124 vac. I will be tracing the electrical conduit from the breaker to where ever it feeds throughout the house- my friend has to remove all the ceiling tiles before I return to do this. At this time, it appears that this 50 amp circuit breaker controls an overhead microwave with a built in the exhaust fan in the kitchen; the receptacle for the refrigerator; the recessed lights- the vanity lights; and the 2 exhaust/light fans to the 1st floor bathroom. In as much as I checked to see if there were any other electrical appliances hooked up to this circuit (e.g. electric stove, etc.)- which does not seem to be the case; Do you think there are loose connections somewhere to have such a major difference in voltage readings between the circuit breaker and the duplex receptacle? I thought the NEC required appliances like refrigerators and microwave ovens to be on their own circuit; lights on another; and receptacle on their own? There are no other branch circuits available in the breaker panel either. Any thoughts? Is this wiring a potential hazard? Please help thank you.


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Old 04-05-2011, 05:31 AM   #2
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Sounds to me like there must be sub-panel somewhere that is fed from that breaker.


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Old 04-05-2011, 07:18 AM   #3
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That portion of the circuit might not be connected and you might be reading phantom voltage.

Plug in an incandescent light, switch it on, and then measure the voltage again. Trying to "use" the phantom voltage will drop it to zero.
The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit.
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Old 04-05-2011, 11:06 AM   #4
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My guess is you are using a digital meter. The voltage was actually off. It was phantom voltage from capacitive coupling.

Last edited by joed; 04-05-2011 at 08:35 PM.
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Old 04-05-2011, 06:56 PM   #5
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Sounds like a major issue there. All these things you mention should not be running directly off a double(220 breaker) and certainly not at 50 amps. As brric said there may be another breaker box somewhere feeding off that 50 amp breaker. If so you'll probably find a tripped single breaker.
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Old 04-06-2011, 12:07 AM   #6
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A big thanks of gratitude to all of you for replying. Today I had the opportunity to trace the lines from the 2 pole 50 amp breaker. It did go to a sub-panel that housed 8 more breakers. Once again, through the process of elimination of turning off each breaker, I was able to determine the branch circuit in the sub-panel that controlled all the bathroom fixtures and receptacles for the first and second floor. The neutral wire that fed the 2nd floor (dead) GFCI receptacle had loosened from its pigtail. I located a maze of wire connections behind the GFCI receptacle in the 1st floor bathroom. Kudos to brric and jayel1! Case closed.


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