Old house, what is going on in this junction box?

[WallyWest]

I've done basic wiring, not a pro by any means. But I know enough to not electrocute myself, which is why I'm not touching this until I understand it. Pic below.

I want to replace that old black cable going from this box to an outlet over my workbench. It's the two wire, no ground type cable and everything else is modern. So just swap cables, replace the outlet with a grounded one, and we're good. Or so I thought. Then I saw that mess.

Here's where all those cables are going.

The black one, as I said is heading over to an outlet. That's it, end of the line.

The two cables coming in from the top of the box both go to the breaker box. One goes straight there, nothing else in between. This, I believe, is the line I'm actually working on. If I turn off the breaker my outlet goes dead. As expected.

But then it gets weird. The other cable also goes to the breaker box, but helpfully has a light outlet in the path. That cable, in the junction box pictured, I don't understand. The neutral wire is hanging, not connected to anything. The hot wire is spliced into the red wire heading out the left of the box. Ground is twisted together with all the other grounds.

The hot wire for the circuit I'm working on is twisted together with the hot from both the black cable and the cable going out the left of the box. Same for the neutral.

The cable going out the left of the box goes to another light socket, and then onto the other side of the basement, and ultimately up to my third floor for some reason. I know that because I have mapped out all the breakers and what they power.

If I turn the breaker that feeds the outlet I want to work on, at the other end of that black cable, it goes dead. The lights however, on both sides of the junction box stay on. I have to flip a different breaker to kill those lights. I took the twist caps off the main connections there, the two sticking down. If I kill the outlet and not the lights I get nothing on a multimeter when I check those wires. But the hot and neutral wire from the left cable, going to a light that is very much on, is twisted into those wires.

Anyone have the slightest idea what's going on here? The obvious answer is to kill both breakers, do what I need to do, and call it a day. But I'd also like to know if this is seriously messed up and I should be looking into it further. I don't understand the left cable. It's got four wires. The normal white, black, and green, and also a red that is spliced into the hot wire from the top that has a dangling neutral wire.

 

[James]

It is not easy to see or fully understand from the description.

However, it seems like you may have 2 circuits sharing the same cable.
In the uk this would be ok, as long as each circuit had its own neutral.
Not sure about the regs where you are.

 

[littlespark]

From this side of the pond, it looks as though someone has “borrowed” a neutral from another circuit.

I’m sure someone like @Megawatt will be able to tell.

 

[Dustydazzler]

Could it not be a 3 plate lighting box ?

 

[Mike Johnson]

I think Dusty has it, looks like a three way lighting box that someone has tapped into for a socket.

 

[Timbo]

What about the switch for the light? Where does that fit in to this circuit?

 

[Lucien Nunes]

The hot and neutral of your outlet circuit are both present in the cable to the left (black and white) along with the red switched hot returning to the light nearer the panel via the 3rd wirenut. But the switch is not taking its power from that black hot, because when you kill that breaker, the lights stay on. Another hot from the second breaker must arrive at the switch via a different route to power the lights.

If you ignore the red switched hot passing through the J-box to the light, everything seems normal, it's just power arriving straight from the panel and splitting to your outlet and the cable to the left. The light has its own neutral back to the panel, it's not sharing the neutral in this box as you point out the white wire is not connected. So far, there is no evidence that the two circuits are cross-connected in a way that would violate code. The pecularity is that the 4-wire cable contains hot and neutral of the outlet circuit heading away from the box, and a switched hot for the light circuit heading towards it. I am not sure if that is code-compliant if they are not part of one multi-wire branch circuit.

What would be interesting though, would be to look in the light between this box and the switch, and find out where it gets its neutral from. If it uses the neutral in this cable (which belongs to the outlet circuit) it's a cross-connection (aka borrowed neutral) and probably a violation. If a neutral belonging to the light circuit arrives from the direction of the switch or panel, again it could be OK.

Some pics of the light and switch would be revealing.

 

[Megawatt]

I've done basic wiring, not a pro by any means. But I know enough to not electrocute myself, which is why I'm not touching this until I understand it. Pic below.

I want to replace that old black cable going from this box to an outlet over my workbench. It's the two wire, no ground type cable and everything else is modern. So just swap cables, replace the outlet with a grounded one, and we're good. Or so I thought. Then I saw that mess.

Here's where all those cables are going.

The black one, as I said is heading over to an outlet. That's it, end of the line.

The two cables coming in from the top of the box both go to the breaker box. One goes straight there, nothing else in between. This, I believe, is the line I'm actually working on. If I turn off the breaker my outlet goes dead. As expected.

But then it gets weird. The other cable also goes to the breaker box, but helpfully has a light outlet in the path. That cable, in the junction box pictured, I don't understand. The neutral wire is hanging, not connected to anything. The hot wire is spliced into the red wire heading out the left of the box. Ground is twisted together with all the other grounds.

The hot wire for the circuit I'm working on is twisted together with the hot from both the black cable and the cable going out the left of the box. Same for the neutral.

The cable going out the left of the box goes to another light socket, and then onto the other side of the basement, and ultimately up to my third floor for some reason. I know that because I have mapped out all the breakers and what they power.

If I turn the breaker that feeds the outlet I want to work on, at the other end of that black cable, it goes dead. The lights however, on both sides of the junction box stay on. I have to flip a different breaker to kill those lights. I took the twist caps off the main connections there, the two sticking down. If I kill the outlet and not the lights I get nothing on a multimeter when I check those wires. But the hot and neutral wire from the left cable, going to a light that is very much on, is twisted into those wires.

Anyone have the slightest idea what's going on here? The obvious answer is to kill both breakers, do what I need to do, and call it a day. But I'd also like to know if this is seriously messed up and I should be looking into it further. I don't understand the left cable. It's got four wires. The normal white, black, and green, and also a red that is spliced into the hot wire from the top that has a dangling neutral wire.View attachment 63831

I've done basic wiring, not a pro by any means. But I know enough to not electrocute myself, which is why I'm not touching this until I understand it. Pic below.

I want to replace that old black cable going from this box to an outlet over my workbench. It's the two wire, no ground type cable and everything else is modern. So just swap cables, replace the outlet with a grounded one, and we're good. Or so I thought. Then I saw that mess.

Here's where all those cables are going.

The black one, as I said is heading over to an outlet. That's it, end of the line.

The two cables coming in from the top of the box both go to the breaker box. One goes straight there, nothing else in between. This, I believe, is the line I'm actually working on. If I turn off the breaker my outlet goes dead. As expected.

But then it gets weird. The other cable also goes to the breaker box, but helpfully has a light outlet in the path. That cable, in the junction box pictured, I don't understand. The neutral wire is hanging, not connected to anything. The hot wire is spliced into the red wire heading out the left of the box. Ground is twisted together with all the other grounds.

The hot wire for the circuit I'm working on is twisted together with the hot from both the black cable and the cable going out the left of the box. Same for the neutral.

The cable going out the left of the box goes to another light socket, and then onto the other side of the basement, and ultimately up to my third floor for some reason. I know that because I have mapped out all the breakers and what they power.

If I turn the breaker that feeds the outlet I want to work on, at the other end of that black cable, it goes dead. The lights however, on both sides of the junction box stay on. I have to flip a different breaker to kill those lights. I took the twist caps off the main connections there, the two sticking down. If I kill the outlet and not the lights I get nothing on a multimeter when I check those wires. But the hot and neutral wire from the left cable, going to a light that is very much on, is twisted into those wires.

Anyone have the slightest idea what's going on here? The obvious answer is to kill both breakers, do what I need to do, and call it a day. But I'd also like to know if this is seriously messed up and I should be looking into it further. I don't understand the left cable. It's got four wires. The normal white, black, and green, and also a red that is spliced into the hot wire from the top that has a dangling neutral wire.View attachment 63831

could you please separate all the wires and leave the wires nuts on them, also the grounds need a wire nut on them so they can’t separate

 

[Megawatt]

could you please separate all the wires and leave the wires nuts on them, also the grounds need a wire nut on them so they can’t separate

Send us a different picture with everything so we can trace all the wires

 

[Megawatt]

I've done basic wiring, not a pro by any means. But I know enough to not electrocute myself, which is why I'm not touching this until I understand it. Pic below.

I want to replace that old black cable going from this box to an outlet over my workbench. It's the two wire, no ground type cable and everything else is modern. So just swap cables, replace the outlet with a grounded one, and we're good. Or so I thought. Then I saw that mess.

Here's where all those cables are going.

The black one, as I said is heading over to an outlet. That's it, end of the line.

The two cables coming in from the top of the box both go to the breaker box. One goes straight there, nothing else in between. This, I believe, is the line I'm actually working on. If I turn off the breaker my outlet goes dead. As expected.

But then it gets weird. The other cable also goes to the breaker box, but helpfully has a light outlet in the path. That cable, in the junction box pictured, I don't understand. The neutral wire is hanging, not connected to anything. The hot wire is spliced into the red wire heading out the left of the box. Ground is twisted together with all the other grounds.

The hot wire for the circuit I'm working on is twisted together with the hot from both the black cable and the cable going out the left of the box. Same for the neutral.

The cable going out the left of the box goes to another light socket, and then onto the other side of the basement, and ultimately up to my third floor for some reason. I know that because I have mapped out all the breakers and what they power.

If I turn the breaker that feeds the outlet I want to work on, at the other end of that black cable, it goes dead. The lights however, on both sides of the junction box stay on. I have to flip a different breaker to kill those lights. I took the twist caps off the main connections there, the two sticking down. If I kill the outlet and not the lights I get nothing on a multimeter when I check those wires. But the hot and neutral wire from the left cable, going to a light that is very much on, is twisted into those wires.

Anyone have the slightest idea what's going on here? The obvious answer is to kill both breakers, do what I need to do, and call it a day. But I'd also like to know if this is seriously messed up and I should be looking into it further. I don't understand the left cable. It's got four wires. The normal white, black, and green, and also a red that is spliced into the hot wire from the top that has a dangling neutral wire.View attachment 63831

I need you to separate the black wire nut and the red so I can see exactly what is going on

 

[WallyWest]

I need you to separate the black wire nut and the red so I can see exactly what is going on

Ok, hopefully this works.

Additional info. The lights in the basement are switched up at the top of the stairs. Two of those light sockets are the kind that have a single outlet on the side of the socket. I know you can wire that so the outlet is still live even when the lights are switched off. Mine are not like that, with the lights off the outlets are dead too. And I checked those outlets with a plug in circuit tester, they both were fine. Had ground, wired correctly, at the outlet anyway.

 

[Megawatt]

Ok, hopefully this works.

Additional info. The lights in the basement are switched up at the top of the stairs. Two of those light sockets are the kind that have a single outlet on the side of the socket. I know you can wire that so the outlet is still live even when the lights are switched off. Mine are not like that, with the lights off the outlets are dead too. And I checked those outlets with a plug in circuit tester, they both were fine. Had ground, wired correctly, at the outlet anyway.

It appears that the red wire is being used as a switch leg

Ok, hopefully this works.

Additional info. The lights in the basement are switched up at the top of the stairs. Two of those light sockets are the kind that have a single outlet on the side of the socket. I know you can wire that so the outlet is still live even when the lights are switched off. Mine are not like that, with the lights off the outlets are dead too. And I checked those outlets with a plug in circuit tester, they both were fine. Had ground, wired correctly, at the outlet anyway.

That is a code violation for sure, as you have stated that the 2 top cables are coming from your panel on separate breakers which if there different phases like 240 vac measured between the 2 live wires really could cause a catastrophic event. I can’t wrap my head around that there are 2 separate live circuits coming in the box. It also appears that the top right cable is being used only as an extra live wire only. You say your a decent electrician so if I was you I would get rid of the cable on the top right because it don’t matter what you are trying to achieve you don’t need but 1 live wire in that box. Like said above you need to take the light or lights apart and figure out the purpose of the red wire and black wire on the left side cable. As stated above it is a violation to share neutrals from 2 separate circuits. It is about impossible for us to be able to tell you what’s going on in the box without taking the first device loose to investigate because it seems the cable on the left is the problem. Get rid of that top right cable

 

[Megawatt]

It appears that the red wire is being used as a switch leg
That is a code violation for sure, as you have stated that the 2 top cables are coming from your panel on separate breakers which if there different phases like 240 vac measured between the 2 live wires really could cause a catastrophic event. I can’t wrap my head around that there are 2 separate live circuits coming in the box. It also appears that the top right cable is being used only as an extra live wire only. You say your a decent electrician so if I was you I would get rid of the cable on the top right because it don’t matter what you are trying to achieve you don’t need but 1 live wire in that box. Like said above you need to take the light or lights apart and figure out the purpose of the red wire and black wire on the left side cable. As stated above it is a violation to share neutrals from 2 separate circuits. It is about impossible for us to be able to tell you what’s going on in the box without taking the first device loose to investigate because it seems the cable on the left is the problem. Get rid of that top right cable

Just replace the old black cable and if your not having problems with the other wiring don’t worry about it. Caution since the neutral obviously shares 2 separate circuits and you turn off just the breaker for the outlet and take the neutrals loose it will spark since the other circuit will still be live. Hell just cut both breakers off and good luck

 

[Lucien Nunes]

Hey MW have a look at my attempt at unravelling it in post #7. I do not see any evidence that the neutral is being shared, because the switched hot (from the 'other' breaker) flies through this J-Box without picking up the neutral, so the light nearer the panel (cable top right) has its own neutral back to the panel. But the light between this box and the switch might be using the wrong neutral, we don't know yet.

If I am correct, can you say whether it is acceptable to use the white and black wires of the left cable as hot and neutral of one circuit (outlet) but the red as the switched hot of the other circuit (lights), provided the two circuits use the proper neutrals?

 

[Megawatt]

Hey MW have a look at my attempt at unravelling it in post #7. I do not see any evidence that the neutral is being shared, because the switched hot (from the 'other' breaker) flies through this J-Box without picking up the neutral, so the light nearer the panel (cable top right) has its own neutral back to the panel. But the light between this box and the switch might be using the wrong neutral, we don't know yet.

If I am correct, can you say whether it is acceptable to use the white and black wires of the left cable as hot and neutral of one circuit (outlet) but the red as the switched hot of the other circuit (lights), provided the two circuits use the proper neutrals?

@Lucien I think that would be bad practice and help me understand that what you are saying the cable on the left is being used for one 120vac circuit and the red is carrying the other live on the top right cable which just has the neutral just floating and not hooked up