Tech / Special Interest → Home Improvement > [Electrical] Overloaded neutral / building wiring fault

[Electrical] Overloaded neutral / building wiring fault

I have a UPS in my wife's home office with an illuminated building wiring fault light. This can apparently happen because of reversed polarity (it's not - at least not at this plug), missing ground, (it's there), and overloaded neutral. I used a multimeter to measure some of my outlets:

The following is edited because I bought a new meter and retested:

#1 Home office outlet:
Hot to Neutral 120V
Hot to Ground 120V
Neutral to Ground 57V

#2 Outlet on same circuit
Hot to Neutral 120V
Hot to Ground 120V
Neutral to Ground 0

#3 Outlet on different circuit
Hot to Neutral 120V
Hot to Ground 177V
Neutral to Ground 57V

I'm guessing I have some issues. What is the best way to troubleshoot this further and what problems could this cause if left unchecked? Is this a DIY fix or should I ignore it or should I call a pro?

Thanks,
Mango

You have a partly open neutral to your house, an extremely dangerous situation. Call the power company as an emergency and they'll find out if the problem is on the pole/underground feeder, at the meter or if it's your problem. Call them tonight!

I forgot to mention it has been like this for the two years I've lived here. I (incorrectly) thought the light on the UPS was due to missing ground but today I noticed a ground wire was there and so I looked further. But I will call them on Monday.

Given that some of the outlets do not have the problem, does that suggest an inside wiring issue rather than a problem on the pole/meter?

Sounds like an open ground, not a neutral as you always have the same voltage from line to neutral.

What kind/brand of meter are you using to test voltages? Get yourself a circuit tester.

This meter: »obrazki.elektroda.net/0_1212514700.jpg

The UPS is an APC Back-UPS ES 350.

Yeah, there should never be 150 volts on a 120 volt socket. A bad neutral will easily do that, but so could a bad meter.

I just tested with a Kill-A-Watt which shows 122 volts at all outlets. The 150V is probably due to a cheap meter. Though I'm still somewhat concerned that Neutral to Ground is showing any voltage at all.

Normal branch circuit voltage is 120 volts so either your meter is badly out of calibration or your line voltage is incredibly high. Over voltage is not likely because of it was stuff would be burning out, incandescent lights and motors.

I agree with the other posts you most likely have an open equipment grounding conductor. The lack of ground is a safety hazard.

/tom

When OP posted such a high reading I thought it might be Peak to Peak rather then RMS but as SparkChaser posted the readings do not match.

/tom

Here are a couple drawings showing shared neutrals. The first one shows the normal concept:

All that information about shared and broken neutrals is correct, but doesn't seem to apply to his situation.

He gets 122V at all outlets measured with a kill-a-watt and 150V at all outlets with a very inexpensive analog multimeter.

To me this indicates that the neutral is good and the ground is missing (either never installed to begin with or subsequently broken).

Voltages can be measured on a broken ground either through a high resistance path (as mentioned earlier) or through induction.
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If it was me I would get a proper meter and make some real measurements. Borrow one if you have to. The kill-a-watt is not a great meter (reads hot to neutral only) and that analog meter is dangerous if it is giving false readings.

If you are on the 250VAC scale and you are reading 50v neutral to ground on that scale, I would want to figure out what is going on. I wouldn't write the whole situation off based on the readings you are seeing on the kill-a-watt. Some cheap digital meters from china will show odd readings on a open circuit but an analog meter will generally not show those spurious readings.

The analogue meter is not reading peak voltage. Like sparkchaser said peak is 169v

Honestly if it was me I would get to the bottom of this. Get a good meter and start in the panel and work out. Make sure the ground and neutral and bonded in the panel (brass screw) and that the voltage is the same to from both hots to ground and neutral. There should be no difference between the two.

So far I have found and fixed:

- Switched neutral on circuit #1 (home office) light.
- Wires stripped too far on circuit #2 light & plug.
- Grounds at multiple outlets not wired to code, but possibly working properly.
- Too many wires in multiple outlet boxes for no reason.

None of this actually solved the problem.

I did notice something helpful. When I shut off circuit #2, circuit #1 tests normal. So I suspect the problem is on #2 but I am going to inspect everything as a matter of course.

Thanks to everyone who has responded so far.

Just to clarify, Circuit 1 is one side of the 220 and Circuit 2 is the other side ?

I'm sorry I don't know. How do I tell?

The 2-pole device can reduce wiring costs and installation time by enabling contractors to use multi-wire branch circuits, commonly known as "shared neutrals". When using single pole CAFCIs, a dedicated neutral is required for each circuit. The new 2-pole CAFCI allows electricians to share neutrals between the two circuits fed by the breaker.