Neutral wire going through a switch instead of hot
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Neutral wire going through a switch instead of hot
I am replacing a light fixture in an old house that has relatively new electrical throughout but still has one remaining knob & tube lighting circuit serving the lights in several rooms.
I'm replacing one of those ceiling lights and noticed the neutral wire (instead of the hot wire) is running through the wall switch on it's way to the outlet box in this room. I determined this by using a voltmeter and putting the black probe into another circuit's grounded outlet and touching the red probe to each of the wires into the outlet box. One read zero, the other 120 volts. The one with zero volts is the one going through the switch. Am I correct then that the neutral is on the switch?
This is knob & tube wiring so both wires are black in color. The wires appear in good condition. Replacing the entire circuit, or even the wire to this one room's switch, would involve removing many walls/ceilings throughout the house which is obviously why no previous owner changed it.
My plan in replacing this light fixture is to tap into the K&T with a junction box and use NM cable for the run to this new light fixture.
The question I have is about the switched neutral. The obvious risk, I think, is that someone would turn the light switch off thinking there was then no energized wire at the light fixture. But, anyone changing a fixture should turn the breaker off anyway, not just a light switch.
If I label the outlet box, wires and panelbox circuit to identify the neutral is switched instead of the hot, is it ok to leave the neutral as the switched wire? Any other concerns I'm not thinking of?
Thanks for all the great advice from this forum.
I'm replacing one of those ceiling lights and noticed the neutral wire (instead of the hot wire) is running through the wall switch on it's way to the outlet box in this room. I determined this by using a voltmeter and putting the black probe into another circuit's grounded outlet and touching the red probe to each of the wires into the outlet box. One read zero, the other 120 volts. The one with zero volts is the one going through the switch. Am I correct then that the neutral is on the switch?
This is knob & tube wiring so both wires are black in color. The wires appear in good condition. Replacing the entire circuit, or even the wire to this one room's switch, would involve removing many walls/ceilings throughout the house which is obviously why no previous owner changed it.
My plan in replacing this light fixture is to tap into the K&T with a junction box and use NM cable for the run to this new light fixture.
The question I have is about the switched neutral. The obvious risk, I think, is that someone would turn the light switch off thinking there was then no energized wire at the light fixture. But, anyone changing a fixture should turn the breaker off anyway, not just a light switch.
If I label the outlet box, wires and panelbox circuit to identify the neutral is switched instead of the hot, is it ok to leave the neutral as the switched wire? Any other concerns I'm not thinking of?
Thanks for all the great advice from this forum.
Last edited by fromhollywood; 07-18-10 at 05:47 PM.
#2
No neutral can be switched. It must be continuous and the hot switched. Hope it wasn't too simple an answer. You hit the nail on the head with your statement about the danger.
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It is certainly a code violation to switch the neutral wire. And it is a BAD IDEA!
I will let the pro electricians comment on "tapping into" K&t, because I am not sure you are allowed to do that. If you mess with this circuit, you may be required to bring the whole circuit up into the 21st century. That would be a GOOD IDEA.
I will let the pro electricians comment on "tapping into" K&t, because I am not sure you are allowed to do that. If you mess with this circuit, you may be required to bring the whole circuit up into the 21st century. That would be a GOOD IDEA.
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Was this the correct way to determine that the neutral is going through the switch?
I determined this by using a voltmeter and putting the black probe into another circuit's grounded outlet and touching the red probe to each of the wires into the outlet box. One read zero, the other 120 volts. The one with zero volts is the one going through the switch. Am I correct then that the neutral is on the switch?
#5
If you are 100% sure the black probe was touching an actual neutral. If your switch was messed up, I wouldn't rely on the other receptacles, etc. A tick tracer is helpful in determining the hot wire when they are separated from each other as your K&T is. Cheap, probably $7.
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What about reversing the wires at the panel?
If I determine that the 5 lights in this circuit all have switched neutrals, won't reversing the wires in the panel fix it?
In other words, I'll take that circuit's wire off the neutral bar and switch it with the one going to that breaker.
Won't that effectively make all the switches on that circuit then use the hot wire?
In other words, I'll take that circuit's wire off the neutral bar and switch it with the one going to that breaker.
Won't that effectively make all the switches on that circuit then use the hot wire?
#7
It could. It could open another can of worms regarding receptacles, fixtures, and switch loops, so just be careful. Determine the hot wire first.
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I guess my idea of reversing the wires inside the panel won't work as one of the light switches on this circuit showed 120 volts at the switch which means it's switching the hot wire as it should be.
#9
IF the neutral is in fact switched, with the switch OFF you should get a 120 volt reading at one side of the single pole switch. Turn the switch on and check it again and you should get a very low voltage to ground reading on each side of the switch, near 0 volts. This would now be a neutral to ground reading. When you switch the hot wire, both screws on the switch will read 120 volts to ground when the switch is in the ON position.
#11
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Is this a 3-way? It may be a Carter 3-way. I've seen this twice in older homes. Look up Multiway Switching on Wikipedia.
Multiway switching - Wikipedia, the free encyclopedia
Multiway switching - Wikipedia, the free encyclopedia
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Would the volt readings at the switch be as you say CasualJoe even though I'm touching the black probe of my clamp meter to a ground on another circuit? This circuit in question is knob & tube so there is no ground. I ran a 3-prong extension cord from a different, newer circuit (with a ground) nearby and used the ground hole on that cord while testing the old K&T circuit.
I had thought finding 120 volts anywhere on a switch meant that it was the hot wire at the switch.
It's not a 3-way switch ArgMeMatey.
Thanks!
I had thought finding 120 volts anywhere on a switch meant that it was the hot wire at the switch.
It's not a 3-way switch ArgMeMatey.
Thanks!
#13
And also very costly $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ wise. For K&T can you just remove the wires at the circuit breaker or fuse box then just do a fishing job with the new wires without ripping walls.
#14
Would the volt readings at the switch be as you say CasualJoe even though I'm touching the black probe of my clamp meter to a ground on another circuit? This circuit in question is knob & tube so there is no ground. I ran a 3-prong extension cord from a different, newer circuit (with a ground) nearby and used the ground hole on that cord while testing the old K&T circuit.
I had thought finding 120 volts anywhere on a switch meant that it was the hot wire at the switch.
It's not a 3-way switch ArgMeMatey.
Thanks!
I had thought finding 120 volts anywhere on a switch meant that it was the hot wire at the switch.
It's not a 3-way switch ArgMeMatey.
Thanks!
Now, if the hot wire is switched, with the switch ON and the lamp lit full bright, you can test each screw terminal with your meter to ground and both screws will show a reading of 120 volts. This is the way it should be and will only allow 120 volts to flow through the fixture and lamp when the switch is turned ON.
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Thanks very much for the helpful suggestions, especially CasualJoe----you should write electrical books as you make things very clear.
I didn't realize that voltage could flow through a fixture and light bulb without the bulb being lit. I'm still a bit fuzzy on that concept. I guess that makes sense as you need a continuous circuit to get electricity to do it's job.
After reading your postings many times to get it into my brain, I retested two of the five switches on this old circuit and clearly have one that is switching the neutral (the one where I am replacing the fixture) and another that is switching the hot.
So, I can't use my idea of just switching hot & neutral back at the panelbox to get all the switches working with the hot wires.
I figured a way to use a 14-3 cable to get the hot to the switch on this one part of this K&T circuit so that should at least allow me to change the light fixture in this one room and know that I'm now switching the hot.
Thanks for the help.
I didn't realize that voltage could flow through a fixture and light bulb without the bulb being lit. I'm still a bit fuzzy on that concept. I guess that makes sense as you need a continuous circuit to get electricity to do it's job.
After reading your postings many times to get it into my brain, I retested two of the five switches on this old circuit and clearly have one that is switching the neutral (the one where I am replacing the fixture) and another that is switching the hot.
So, I can't use my idea of just switching hot & neutral back at the panelbox to get all the switches working with the hot wires.
I figured a way to use a 14-3 cable to get the hot to the switch on this one part of this K&T circuit so that should at least allow me to change the light fixture in this one room and know that I'm now switching the hot.
Thanks for the help.
#17
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I never had K & T. My old 1920s cloth and rubber BX was in good shape inside the walls, but at the devices it was flaking apart. We "made safe" some sections by disconnecting them but ultimately rewired the whole house. Most people won't do that due to cost and inconvenience, but I sleep better now.
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3 Ways
We used to call them _astard three ways...
In the knob and tube days they used the neutral for one of the travelers for the 3 way switches. Usually I would get a call when someone would replace their 3 way switches and they would start popping the breaker. As long as the insulation is still in good shape where it enters the boxes the installation is safe. They are separated with one wire on each side of the studs which makes distance your safegard, 120 volts is not going to jump 16".
Best of luck...
In the knob and tube days they used the neutral for one of the travelers for the 3 way switches. Usually I would get a call when someone would replace their 3 way switches and they would start popping the breaker. As long as the insulation is still in good shape where it enters the boxes the installation is safe. They are separated with one wire on each side of the studs which makes distance your safegard, 120 volts is not going to jump 16".
Best of luck...