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Old 03-18-2008, 12:31 AM   #1
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Building wiring fault


My surge protector has shown a light labeled "Building Wiring Fault" since I moved it to a different room. I used a multimeter to check the voltages between the prongs on the outlet, and this is what I found:

Hot/neutral 116 volts
Hot/ground 69 volts
Neutral/ground 46 volts

Please correct me if I'm wrong, but I thought the Hot/neutral and Hot/ground should read approx 115 volts and Neutral/ground should read 0 volts.

The house is fairly old (around 55 years) so the grounding may not be original.

Can anyone tell me what the readings should be, and what could be causing the problem? Thanks!

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Old 03-18-2008, 12:59 AM   #2
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Building wiring fault


The outlet you're plugged in to is not grounded. At least not all the way back to the panel. If it is actually grounded, then the main bonding jumper is either loose of missing. Considering the age of the building, I suspect it's not grounded at all.

Rob

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Old 03-18-2008, 10:10 PM   #3
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Building wiring fault


The readings should be 120 as you suspect. I'm thinking it may be bigger than just the outlet. Although it is definitely a ground problem. Check your other outlets in the house and see if you get similar readings on some of the circuits.

Does this sound like a floating neutral to anyone else?
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Old 03-18-2008, 10:35 PM   #4
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Building wiring fault


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Originally Posted by goose134 View Post
Does this sound like a floating neutral to anyone else?
46 VAC Neutral/ground is a pretty squirrelly reading... yes.

I'd say you are right.
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Old 03-19-2008, 11:00 AM   #5
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Building wiring fault


Quote:
Originally Posted by sparky120/240 View Post
Quote:
Originally Posted by goose134
Does this sound like a floating neutral to anyone else?
46 VAC Neutral/ground is a pretty squirrelly reading... yes.

I'd say you are right.
NO since you have 116v hot to neutral and 69 volts H-G, I would say you have a floating or open ground. The neutral is fine.

Last edited by joed; 03-19-2008 at 11:03 AM.
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Old 03-19-2008, 06:15 PM   #6
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Building wiring fault


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NO since you have 116v hot to neutral and 69 volts H-G, I would say you have a floating or open ground. The neutral is fine.
By definition,a floating neutral is a neutral conductor whose voltage to ground is free to vary when circuit conditions change. The neutral being the grounded conductor, it is related to a bad ground, I agree. If multiple grounding points are established (bonded sub panels are a prime example) the equipotential of the grounding plane is thrown.

What to do? Yes, there may in fact be an open ground somewhere. Possibly in one outlet, maybe elsewhere. I would check to see if the neutrals are spliced correctly in the outlet first. If that doesn't do it, start trying to see where else the problem is. Only one phase, only one circuit and so on.
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Old 03-19-2008, 08:06 PM   #7
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Building wiring fault


There might not even be a ground present in the box. Could be someone installed three prong receptacles on an ungrounded circuit.
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Old 03-19-2008, 08:07 PM   #8
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Building wiring fault


The only way to know for sure is to test with load. A multimeter has a very high input impedance, and doesn't load the circuit at all. If you rig up a 100 watt light bulb to some wires, and stick one into the hot side (the smaller slot), and the other into the neutral, and it lights, the hot and neutral are fine. If you go from the hot to the ground, and it doesn't light, that proves a problem with the ground. Neutral to ground shouldn't light it either. Just make sure nothing else is on the circuit during the test.

The one exception to this test would be if there's a GFI or AFI upstream. Either one will trip hot to ground. To prove or disprove this, simply test hot to ground, then hot to neutral. If the GFI or AFI tripped, the hot will be dead.


Rob

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