Weird Voltage on one Circuit

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Old 10-06-19, 10:59 AM
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Weird Voltage on one Circuit

Yesterday I was using an electric hedge trimmer and nicked an extension cord with the trimmer while it was running. I saw the flash and heard a pop. I traced down the appropriate GFCI breaker and reset it and I was back in business.

Later in the day I noticed a different circuit was not working properly. I checked the voltage on the three indoor outlets with a DMM and measured 16 volts . These three indoor outlets are physically close to an outdoor outlet that incorporates a GFCI. I suspect the same cable provides power to all four outlets but the outdoor outlet reads less than a volt. I then pulled the front panel off the breaker box and measured the voltage at the output of the breaker: 120 V.

So 120 volts feed that circuit but only 16 V (?) gets to the three indoor outlets and less than a volt to the outdoor outlet. What could explain this?

Also, somewhere in the sequence of making measurements, tripping and resetting GFCI's, etc I noticed a bunch of breakers (about 8) all in a row in the electrical box had tripped out. I reset them all without a problem.
 
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Old 10-06-19, 11:14 AM
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Perhaps the circuit is dead at that point and the voltage readings are meaningless.
8 breakers tripped? What type? Standard, GFCI, AFCI, GFCI/AFCI?
 
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Old 10-06-19, 11:15 AM
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Is everything OK now that you reset the breakers?

The 16 volts is most likely ghost voltage.
If you run an wire next to a wire with AC on it you will induce a voltage in the wire.
This is basically how a transformer works.
There is voltage there but no real amperage.
 
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Old 10-06-19, 11:18 AM
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8 tripped breakers in a row may have been the panel cover hitting them when you took it off.

You measured from the large slot to the small slot and saw low voltage.
Try measuring from the small (hot) slot to ground. There should be 120v measured.
If yes.... you have lost the neutral.

That will require you to identify everything on that circuit. You need to determine if everything is dead or only some of the devices. The problem will be at the last working or the first dead device.
 
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Old 10-06-19, 03:31 PM
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I think you're right about the tripped breakers being due to the front panel hitting them when I took it off. I recall one of the top most corners not releasing easily and battling with it a bit.

All of the 3 indoor outlets measure 120 V from the narrow slot to ground. The outdoor outlet with the GFCI breaker measures 2.5 V narrow slot to ground. If I measure between the black (hot) wire to ground on the back of the GFCI breaker I get 120 V. I notice that I can't trip the breaker or reset it using the buttons on the front of it. So it seems like the GFCI breaker has given up the ghost.

But here's the thing--there's only one piece of Romex that attaches to the GFCI breaker. So either it's the last of the four outlets on this string or there's something else wired to this circuit the I'm not aware of. How would a failure inside the GFCI cause the other outlets to NOT have 120 V? What's my next step?
 
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Old 10-06-19, 05:05 PM
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A GFI receptacle will not set/reset without 120v on the hot and neutral wire.
If there are only 4 devices on the circuit..... and you know the GFI receptacle is the end of the circuit..... go to the device closest to the panel and start checking inside that box.
 
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Old 10-06-19, 05:27 PM
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A GFCI will not reset unless there is 120 vac connected between it's line and neutral terminals. What do you read between the small and large slots on the indoor outlets? If not 120 vac, there is a problem with a neutral connection in the circuit.
 
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Old 10-07-19, 07:36 PM
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OK, so I dug into the receptacle I believe is the closest to the panel. It's just a simple duplex outlet. All the 5 terminal screws are tight and the jumpers are intact and measure 0 Ohms. There are no burn marks or other damage visible. Tomorrow I will trace the wiring to make sure I'm looking at the closest device to the breaker panel.

Anything else I can check?
 
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Old 10-07-19, 08:09 PM
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Did you check for voltages there ?
 
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Old 10-07-19, 08:59 PM
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Slot-slot = 16 V
Narrow slot to ground = 121 V
Wide slot to ground = 105 V or 0.6 V (flaky readings)
 
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Old 10-07-19, 09:39 PM
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Ok.... so at that point you are still missing the neutral.

See if you can follow this.
Here's what I do..... remove one black wire from the receptacle. You've now opened the hot line. Check the other receptacles. The problem will not be at a dead receptacle. It will be at one of the working ones.

Reasoning..... you have power from the panel there but not neutral. The problem is in between that receptacle and the panel. Everything that's dead is after that receptacle.
 
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Old 10-08-19, 12:24 PM
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You Are the Man!!!

My wife noticed another outlet without power. It was in the right location to be on the same run. So I just removed the receptacle from the box and checked out the connections. And there it was--one of three white wires joined with a wire nut had somehow pulled loose creating the "lost neutral" you had predicted.

I would never, ever have found this without your help. Thank you so very much!!!!
 
 

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