AC electrical puzzlement

[Bill Howatt]

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I never heard an answer to the question if anything was plugged into any outlet in that circuit. That will tell us a lot, especially if unplugging whatever that is makes a difference.

This would be good information and if I were to guess, I'd say something is plugged in. This is the only way you can get 120V to ground off the neutral since the 120V has to feed through a device (very, very little current required)to cause a high-impedance voltmeter to read 120V.
I would start at the panel and ensure the neutral was well connected and then hopefully be able to follow the circuit from the panel to the end. You need to leave the whatever is plugged in, plugged in, so you have a voltage on the neutral to measure. As long as you are in the properly connected chain from the panel the neutral to ground voltage should be 0.
OTOH, you could just go through all the receptacles especially if back-stabbed. There is a good chance you will some physical signs on the offending connection such as melted plastic insulation, burned off wire, or very discolored copper wire (or screws if used).

[George Yetka]

I would like my house to be at the studs with no wire so that I can start from scratch and wire it. Even if I was heavily drinking while doing it I can do it better than how it currently is.

Countless wire nuts buried in the walls.
Countless overloaded L&R breakers
Items wired nonsensically. 1st floor dining room, family room, & 1/2 kitchen, outlets and lights in bedroom upstairs and basement water heater on 1- 15 amp breaker
I have 1 GFCI outside that if tripped will make me lose lighting in a pantry closet and the light right outside of it.(nowhere near the outdoor GFCI)
Master bath GFCI will make me lose front side of the house recepticals.
Upstairs wiring has no switch to light or switch to fan home runs they are all pieced together out of 2-4 piece of romex.
When I moved in there was a lamp cord coming out of a light switch cover that I realized when plugged in turns on a light outside.

Ive spent alot of time breaking up circuits and replacing spliced wire.

[Curt Harms]

Well, I found the problem

wires2.jpg

It looks like back stabbed connections strike again. the fact that the box is in a brick rather than in something combustible is some comfort but I don't know how close to combustion temperatures browned neutral wires indicate. I will either re-wire or replace back stabbed devices as I'm able to gain access. Some outlets are behind large heavy furniture.

Two of the 4 known outlets on this circuit are the ones that have the highest loads, mostly electric lawn mower and occasional portable air compressor. It's a 15 amp circuit - thought it was 20 amp but nope - so it wouldn't be hard to load in excess of 80% of rated amps. The only other significant load I can think of in the house is a laser printer. Those draw quite a bit of power when printing but the load is brief, one or two sheets of paper. The kitchen appliances are all on 20 amp circuits but I don't know how they're wired, back stabbed or not.

[Tom M King]

Glad you found it. I like to use 20 amp receptacles even though code allows 15 amp. Most slightly heavier duty 20 amp receptacles these days have a good connection system that allows straight stripped wires coming into the back. Rather than just relying on a small spring piece of sheet metal to provide the contact, they have a heavier plate that pulls up against the stripped wire end with a machine screw.

I have been known to use an aircraft rivet bucking bar and a hammer to flatten the stripped end of the wire to give it a little more surface area of contact inside that clamp plate.

[Bill Howatt]

80% of the rated amps has little to do with it, you would have the same problem on a 20A circuit with the same type of connections. The problem is the back-stabbed connections got bad and went from close to 0 resistance to some value. The current through this resistance caused heating - the so-called I-squared R heating (watts) and each time the connection heats up it can increase the resistance and cause even more heating. As an example, say your load is 10A and the resistance of the connection increases to just 1/4 ohm this would create 10*10 *0.25=25watts in a very small area (the back-stab) and certainly would cause heating. Another issue depends on the circuit topology, if the outlet you use with the high current loads, like the lawnmower are at the end of the circuit chain, that current has to flow through all the other connections from/to the panel. These receptacles may be showing the effects of heated connections also. Good clean screw connections will solve the problem.

[Doug Garson]

Glad you found it. I'm not an electrician so I'm having trouble understanding how a bad neutral connection leads to a hot neutral. Can any of the Sparkies explain it? I would have thought you would need a short between the hot and neutral to cause the neutral to become hot.

[Tom M King]

It only makes the loose neutral hot when something is plugged into an outlet on that circuit. The connection is made inside whatever is plugged in. The breaker would trip if there was a short, but in this case the loose neutral now can carry the hot load but there is no real short because the now energized neutral is not bonded. Nothing works when plugged in downstream because there is no bonded neutral to complete the circuit. That's why I asked to start with if anything was plugged into that circuit.

I've seen this exact thing twice before on old back stabbed device circuits.

[Dan Friedrichs]

Glad you found it. I'm not an electrician so I'm having trouble understanding how a bad neutral connection leads to a hot neutral. Can any of the Sparkies explain it? I would have thought you would need a short between the hot and neutral to cause the neutral to become hot.

Imagine a load like a heater (which is just a piece of resistive wire) is plugged in, but the neutral connection is broken at the panel. The 120V flows from the hot, through the heater, to the neutral, causing the neutral to have 120V on it.


Glad you found it, Curt. When we bought our last house, one of the first things I did (before moving furniture in) was replace all the old receptacles and light switches with matching, higher-quality versions, and use screw terminals (no backstabs). Only took a few hours and not that much cost.

[Tom M King]

Both of the such circuits that I found like that were in a rental house I bought cheap because it was considered a tear-down for many reasons. It also had one circuit that nothing would work on some outlets unless something was plugged into one receptacle in that circuit. I didn't bother to even think about that one. I just pulled all the devices and replaced every one of them. I think that work was originally done in 1974. Everything works fine now in it.

[Doug Garson]

Tom, Dan, thanks for the responses, makes sense, I wasn't aware that a loose neutral could be that dangerous. As far as I know, none of the outlets or switches in my house are back stabbed, any I've done or looked at are connected using the side screw terminal.

[Tom M King]

I don’t know when they finally went out of favor. I never used them in any of the house I ever built.

[Curt Harms]

I don’t know when they finally went out of favor. I never used them in any of the house I ever built.

I don't know either, maybe after the 10th house fire they caused? I had previously rewired the appliance receptacles with the heaviest loads - microwave and toaster oven - except for the refrigerator which is very difficult to access the plug.

[Jack Frederick]

I am weak electrically. I learned about proper wiring of receptacles, grounding having to trouble shoot the heating equipment I sold, in this case the Rinnai Energysaver DV wall furnaces. They are extremely reliable and early in the game I took the bait. The unit doesn’t work, it must be the unit and I would get lost testing out every leg off the board. Still intermittent operation. Today’s appliances, the better ones all use flame rectification to prove flame as pilot lights are long gone. Tech services is telling me to check the ground. The ground is testing good. I can’t get 24 hours of good operation out of the unit. Before replacing it I asked the owner if I coulld run it off an extension cord on another circuit. He was a great and very patient guy. We did it and the unit just purred along. I went back, pulled the receptacle and as it came out the hot and ground stayed “stabbed in”. The neutral stayed in the box pointing out at me. Sometimes it would make, sometimes not. Terminated the screw connections on the receptacle and that unit is probably still running 25 yrs later. Stab in connections became a primary discussion in all the contractor trouble-shooting classes I did in the years after.

[Jim Becker]

I don't know either, maybe after the 10th house fire they caused? I had previously rewired the appliance receptacles with the heaviest loads - microwave and toaster oven - except for the refrigerator which is very difficult to access the plug.

Curious, Curt...about when was your development built? This house here near DelVal went up in 1993 and it's "chock full" of back stabbers and other interesting things.

[Cameron Wood]

I don't know either, maybe after the 10th house fire they caused? I had previously rewired the appliance receptacles with the heaviest loads - microwave and toaster oven - except for the refrigerator which is very difficult to access the plug.

I have twice traced dead circuits to the refer receptacle- vibration and/or cycling had work hardened the wire at the terminal causing it to break.