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

Re: [Electrical] Overloaded neutral / building wiring fault

Thanks for this - along with StillLearn's picture above I finally understand this concept.

1) No, both are black. The only red wires are one from the supply and one to my clothes dryer.
2) Different cables, each with its own neutral.
3) Complete opposite ends of the right side of the panel.

I think the answer to SparkChaser's question is yes, #1 is on one side of the 220 and #2 is on the other side. The neutral is not shared.

I just discovered this:

Circuit #2 has no ground to the panel, but does have a ground wire at some of the boxes. The ground for #2 is connected to #1 at a box that contains switches for lights on both circuits. There is also a ground wire running from one of the lights on #2 to a receptacle on #1.

Unfortunately I don't have a good way of doing that, without taking out walls.

The neutral isn't shared. I don't mind calling an electrician if this is more than a DIY fix but I would like to understand the problem.

Do they sell anything like the Simpson 260 anymore?

We don't know that Mango did not use one of these: »www.tequipment.net/ProtekA450.asp with a 10 MOhm input impedence.

In the 250V AC setting this multimeter has an input impedance of 500k. While significantly less (1/20th) then the typical 10M of a digital voltmeter it would still be high enough to show a reading from capacitive coupling.

However I wouldn't be surprised if any stray voltages measured on the disconnected ground aren't the direct result of the circuit test inside the APC UPS!

I have an older APC SmartUPS (with circuit test LED) that shows a red light because the (GFCI protected) outlet doesn't have an equipment ground. Measuring the voltage between Ground and Neutral with a DVM while the UPS is connected I get a reading of 56V AC.
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I'm not going to argue specific voltage readings on an instrument that shows a reading of 150 when measuring 120V AC.

In order to get a real 50V reading on a multimeter with 500k impedance the ground wire would have to be coupled with 3.8nF to the hot wire (120V AC) only. In a real scenario the ground wire will have roughly equal capacity to all other wires in the cable (neutral and hot) which will make 1/2 the hot voltage (60V AC) the upper limit even before taking the load through the measuring device into account.

50V AC through capacitive coupling in the cable is extremely unlikely in a home, the cables are simply not long enough to get to the required capacity.
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There is a distinct possibility that the ground to neutral voltage that you are measuring is coming from the circuit tester inside the APC UPS. If so, you can use that to your advantage and narrow down where the ground is interrupted in your home.

To confirm this theory please attach the UPS to the outlet where it was originally connected when you first discovered the issue with the ground to neutral voltage (the UPS may have to be on). See if you get the high ground to neutral voltage reading again. If so, disconnect the UPS and measure the same outlet again. If the theory is correct the ground to neutral voltage should be gone or at least much lower.
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if you want to know which is faulty, the neutral or ground, measure the AC voltage between those and a water pipe(only a full copper pipe from the meter), they should stay at 0 volts. if you measure a voltage at either one to the water pipe, that's the bad one, then you have to go through that whole path, to find where the bad connection is.

I found an interrupted ground wire on the supposedly grounded circuit. I worked out how to fish a ground wire to this and the ungrounded circuit. I grounded them to another circuit that has proper ground. I was previously told not to do this but now I have a new inspector who states he will pass this when he sees it later. As the posts above predicted, that solved most of the problems.

I also found severely degraded insulation on wires at a ceiling light. It was so bad I decided not to touch it and had an electrician fix this one.

I'd like to thank everyone who gave me advice to help find the problems. I learned a lot.