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Discussion Starter · #1 ·
I posted this question first on "Electrician Talk", but got booted off of there as I am not (nor have I ever been) a licensed electrician.
I do, however, have a masters degree in electrical engineering which should count for something.
They told me to come here. So here I am.

Anyway, as I was unscrewing the top mounting tab screw on a switch I was replacing, it started sparking mildly.
I thought to myself, "Hmm... That's interesting. Something isn't quite right here."

Closer inspection showed that someone, at sometime in the distant past, had taken the neutral conductor coming in to the switch outlet box and clamped it under the top switch mounting lug, so that the neutral for that branch circuit now consisted of a number of sections of external BX armor, outlet boxes and rigid conduit going down to the main panel.
The house was built in 1920, using 14-2 BX cable and rigid conduit throughout. There is no knob-and-tube wiring anywhere.

On the affected branch circuit, a number of wall and ceiling luminaires branch out from the switch outlet box. Power to the switch box is supplied from a wall receptacle outlet that goes to 3 other wall receptacle outlets (in some unknown order) before making its way down to the old main panel and entering the panel through one of 5 rigid conduits.

After removing all of the loads on that circuit, the measured resistance from the neutral wire to ground is infinite. There are no other neutrals in/out of the switch box.

I hesitate to disassemble all of the connections in the outlet boxes on that branch circuit to trace the wiring, as the old fabric-covered wire is intact but the rubber insulation is hardened and breaks easily.

I suspect that when a new main breaker panel was installed around 1977 next to the old fuse panel, the installer may have lost the neutral for that branch circuit. Every old wire coming into the old main panel is black, whether they are hot or neutral.

Has anyone got any troubleshooting advice on how to hunt down the broken/missing neutral and/or install a new neutral for that branch circuit?

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masters degree in electrical engineering which should count for something.
Me too. Don't count on it. :D

as I was unscrewing the top mounting tab screw on a switch I was replacing, it started sparking mildly.
Current in what is supposed to be ground.

hunt down the broken/missing neutral
Rent a Time Domain Reflectometer but it may not be worth it to you & for this job.
 

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Holy spaghetti! They used a panel box as the splice box? So many circuits. Is the problem circuit the 7th down on the left? Labeled #13? So your circuits are all ungrounded? And someone used the armor jacket as a "neutral". A pic of that switch would help. Looks like u have conduit to run a new neutral to that switch. Would take some planning if it goes through multiple junctions. If a black wire is in that switch box then you should be able to fish a neutral and then fish the black back through. Still ungrounded. Have you identified which black wire goes to the switch?
Plus figuring out how a wire jacket was a neutral conductor. Just for due diligence/safety.
 

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There may be a way to find the break with only a C-meter if you know how the cable is routed.

All these cables have some number of picofarads per foot between conductors. For Romex, it’s about 100 pF/ft.

With a sample of your cable you can find this value & then measure between each conductor. The capacitance to the broken neutral conductor should be less.
 

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New kind of Bootleg ground/neutral.

To some of our pro's........when was a grounded system required or in normal use.??????

OP said:"The house was built in 1920, using 14-2 BX cable and rigid conduit throughout. There is no knob-and-tube wiring anywhere. "

When wiring with the old original BX (in the 1920's) was the intent of the BX to act as a ground (when presumably grounding was not required) or just as a protector over the wire.

To the OP.....is your home in Chicago>..????
 

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Just trying to think.....if OP's assumption is that a "black" neutral was lost/misplaced in the transition from the old to new panel.......then that black neutral must have been spliced to black hot into the new panel (assuming you don't have a loose black wire in your old panel.

If so, that original black neutral is now a hot as everything in the new panel is wired correctly......so maybe that "neutral you think is connected to your switch, is actually a hot.....and you should have two hots in that J box.

If so, the answer to chase down would be to throw off breakers untill that second hot is broken, and then rewire that black over to a neutral.

No?????
 

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Yup. Definitely need a photo of the switch box and everything in it. If rigid or emt is used then where did the armored jacket enter the scenario? Is it from the light and they just grounded the neutral thus energizing everything metal in your house? Wouldnt that kill someone or at least trip the breaker?
 

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Discussion Starter · #9 ·
I'll try to reply to everyone in this post.
First, here's a shot of the switch box. Switch box is on the 2nd floor.
Only 6 wires coming in, that's all. The only neutral coming into the box is the white coming in from the bottom.

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Rent a Time Domain Reflectometer but it may not be worth it to you & for this job.
Last time I used a TDR was 23 years ago. The biggest problem with that approach is that I cannot identify the missing neutral coming into the old main panel. By the way, I just saw plans for a DIY TDR on Instructables. I might just build one.
Is the problem circuit the 7th down on the left? Labeled #13? So your circuits are all ungrounded? And someone used the armor jacket as a "neutral". A pic of that switch would help. Looks like u have conduit to run a new neutral to that switch. Would take some planning if it goes through multiple junctions. If a black wire is in that switch box then you should be able to fish a neutral and then fish the black back through. Still ungrounded. Have you identified which black wire goes to the switch?
Yes, it's circuit #13. Yes, I'm pretty sure all circuits back in 1920 were ungrounded. Grounded receptacles first showed up in the 1947 NEC. BX cable, first used in 1898, was to protect the conductors rather than be used as a ground. Yes, the BX armor jacket was acting as the neutral for that one circuit. Yes, I could run a new neutral in the existing rigid conduit, but only for a short distance of about 20 feet, where everything transitions to BX at various outlet boxes. I can't fish a neutral through any of the BX sections. Not enough room. Too many bends. Don't have the skills.
There may be a way to find the break with only a C-meter if you know how the cable is routed.
All these cables have some number of picofarads per foot between conductors. For Romex, it’s about 100 pF/ft.
With a sample of your cable you can find this value & then measure between each conductor. The capacitance to the broken neutral conductor should be less.
That is a really interesting idea. I do have a capacitance meter, but I have no idea how the cable is routed. The switch box is on the 2nd floor, it goes to a number of other outlets and the basement ceilings are all finished. A metal detector might help.
To some of our pro's........when was a grounded system required or in normal use.??????
When wiring with the old original BX (in the 1920's) was the intent of the BX to act as a ground (when presumably grounding was not required) or just as a protector over the wire.
To the OP.....is your home in Chicago>..????
The home is in Milwaukee, North of Chicago.
The first NEC grounding requirement seems to be in 1952 for washing machines.
Logically, it seems that the invention of BX was to provide a flexible wiring system that would protect wires.
Just trying to think.....if OP's assumption is that a "black" neutral was lost/misplaced in the transition from the old to new panel.......then that black neutral must have been spliced to black hot into the new panel (assuming you don't have a loose black wire in your old panel.
If so, that original black neutral is now a hot as everything in the new panel is wired correctly......so maybe that "neutral you think is connected to your switch, is actually a hot.....and you should have two hots in that J box.
If so, the answer to chase down would be to throw off breakers untill that second hot is broken, and then rewire that black over to a neutral.
That's an interesting thought. The only black coming into the switch box is hot and connects to breaker #13.
The white "neutral" coming from from the wall receptacle outlet (along with the black hot) measures infinite ohms to "BX ground" when the circuit breaker is open and all loads have been removed from circuit #13. Somewhere along the way from the switch box to the main panel, the "white neutral" was spliced to become a "black neutral" along with all of the other neutrals when the original house wiring was installed.
If rigid or emt is used then where did the armored jacket enter the scenario? Is it from the light and they just grounded the neutral thus energizing everything metal in your house? Wouldn't that kill someone or at least trip the breaker?
Rigid conduit was used throughout the basement on the exposed surface of the plaster-finished ceiling, and goes throughout the basement to many, many splice boxes. All these splice boxes then transition the wiring over to BX which then disappears up into the plaster ceiling.
I don't believe that the grounded neutral has dangerously energized the conduit and BX armor. After all, the neutral bus bar and conduit grounds are joined together in the main panel as per code. , Your concerns are justified, however, as that path of BX armor sections, outlet boxes and conduit from the switch box to the main panel were carrying the full current load of that circuit even though the voltage measured, under load, between the BX armor and ground at the main panel would be pretty close to 0 volts.
 

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Alright. It might help to separate them more since i can't follow all the wires with the shadows. I misunderstood how the bx armor came into play.. yeah, pulling wire through bx is probably possible but it seems you should have what you need. The detail that puzzles me is why 2 hots are going to the upper right light. Looks like 1 hot is under the yellow nut and the other is under the orange [dimmer]. Both going upstream to the load? Something seems wrong with that dimmer splice other than using thin brown lamp wire as a splice. If you have a switch leg then one of your hots should be switched but it looks like they are both always hot. Is that because you don't have the switch wired in there?
What is the wiring of the light itself look like? Do some continuity testing and label the hot and neutral at the light. Or course the neutral of the light may never pass through that box. Did the light ever work?
 

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Discussion Starter · #12 · (Edited)
The detail that puzzles me is why 2 hots are going to the upper right light. Looks like 1 hot is under the yellow nut and the other is under the orange [dimmer]. Both going upstream to the load? If you have a switch leg then one of your hots should be switched but it looks like they are both always hot. Is that because you don't have the switch wired in there?
What is the wiring of the light itself look like? Do some continuity testing and label the hot and neutral at the light. Or course the neutral of the light may never pass through that box. Did the light ever work?
Here is a clearer picture of the switch box wiring.
I agree. The more I look at this the more confused I get. Nothing makes any sense. Yes, two hots appear to go to the ceiling luminaire which makes no sense. Perhaps the left hot goes to some other load. I have no idea how neutrals are provided for either the ceiling or the wall luminaires. The taped-off conductor going to the wall luminaire looked like it had been taped off when originally wired. I will open up the ceiling light wiring to take a look. I don't see any switch legs in the wiring. Your sketch is certainly what the wiring should like. I wish I knew where the light fixtures were getting the neutrals from. Yes, the lights always worked until I took everything apart.

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I think this is all you have plus another switch and light. Add the switches and it should come together. That taped off wire to the wall light was important and got eliminated. Confirm its the neutral and splice it to the other neutrals. That brown lamp wire is confusing things. Use some 12 gauge and add a switch
 

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I do, however, have a masters degree in electrical engineering which should count for something.
Actually it works against you because you have lots of stuff to unlearn. Code electrical work has all the engineering "engineered" out of it, and it's a "paint by numbers" deal. EE's always want to do something clever or original. It's like the job is paint a building off-white, and you're Banksy.


I hesitate to disassemble all of the connections in the outlet boxes on that branch circuit to trace the wiring, as the old fabric-covered wire is intact but the rubber insulation is hardened and breaks easily.
Well, if you have the access and ability to simply replace all the wires in the old pipe, don't be afraid to get some THHN wire and go to town.

Holy spaghetti! They used a panel box as the splice box? So many circuits.
That's not a problem. The trick is to mark it with colored electrical tape.

They make 10 colors of that (same colors as the resistor color codes)... shouldn't use black/white for confusion reasons, so that leaves 8 colors to use. I see 5 pipes and surely less than 8 circuits per pipe. Shouldn't be a problem.

Since it's THHN wire, re-marking white wires to be hots is not allowed. So a white wire with blue-yellow markings is the neutral for blue-yellow circuit, not a hot.
 

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So the wire with the black hatch marks in the insulation is treated as black? Those are the 2 switch legs. But without the switches this is incomplete. Id start with one light at a time...add the dimmer between the orange wire nuts...and take the all white wire from that light and put it with the neutral from the outlet.
But to start confirm where those light wires are terminated on the light itself.
John, I think it looks like no wires are missing [other than a ground] but without the switches this is not complete. And the hots and neutrals might be swapped. One insulation is all white and the other has black stripes in it. That is the detail to look for when wiring with his 1950s insulation.
 

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Discussion Starter · #16 ·
That taped off wire to the wall light was important and got eliminated. Confirm its the neutral and splice it to the other neutrals.
You got it right. Scraping the oxidation off of conductors, doing some more wire tracing, and examining other wire boxes on the circuit confirmed that the neutral was coming from the wall light fixtures and the hot was coming from the ceiling fixture. I had assumed neutral and hot were coming from the wall receptacles, which turned out to be totally wrong.
First time I've ever been wrong my entire life. Go figure.

Anyway, here's what it looks like when wired correctly. Wires were all scraped, soldered, and then self-vulcanizing rubber taped, with friction tape over the rubber. (old-school)

I still don't know why the neutral was taped off on both ends some 50-70 years ago. Unfortunately, whoever did it is long-dead.

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Ah...you did not have a switch leg cuz the wires came through the fixtures first. That makes it hard to diagnose. I thought the power was originating from the outlet area but was wrong. I still do not see the switches wired in. Will it work now? The only detail I don't like is the neutral from the wall lights has black hatch marks....so it should be the hot but looking at that junction panel almost all the wires leaving it are black so i see 50 black leaving and only 3 white but 20 of those black are really neutral. Hard to say what you can do there.

Yes the friction tape and cloth insulation is a real pleasure to work with. But replacing it involves a bunch of holes in the walls and ceilings. With conduit you can replace it to a point pretty easy. I had knob and tube and just replaced all of it. Not sure why this house didnt burn down with bare wire touching metal boxes everywhere.
A gfci outlet at the start of those branches will give you some protection in lieu of a ground wire. Or just dont mess with it is an option. Putting a gfci at that outlet for example will protect only that outlet. The gfci has to be first in the branch and then wire everything off the load terminals and you will have some protection...and an outlet with three holes. Just put the sticker that says "no ground present".
 

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Discussion Starter · #18 ·
I still do not see the switches wired in. Will it work now?
I decommissioned the two wall light fixtures, so I removed the switch to them as well.
The ceiling dimmer is still wired in with the zip cord wiring replaced.
Everything works now, even the grounds on the grounded receptacles.

The only detail I don't like is the neutral from the wall lights has black hatch marks....so it should be the hot but looking at that junction panel almost all the wires leaving it are black so i see 50 black leaving and only 3 white but 20 of those black are really neutral. Hard to say what you can do there.
The three white neutrals in the junction panel are all new circuits added in.
It appears that two types of BX conductor marking were used in the house.
Black and white when daisy-chaining from wall receptacle to receptacle,
and white and white w/black hatching everywhere else.
The white w/black hatching seems to be there so that the conductors at both ends of a BX section can be identified.
White w/black hatching is used throughout the house for neutrals, hots, switched hots, switch legs, etc.---everything but wall receptacles.
 
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