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  1. #1
    Join Date
    Apr 2012
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    Question Completely Perplexed.

    Part of my house has the old knob and tube wiring, so any chance that I have to replace it I do. There’s very little of it left. The other day I went to replace an old light switch in the basement with a occupancy sensor. The only other thing on this circuit breaker is my freezer. Replacing this light switch should have been a simple enough job, but replacing this light switch has turned into a can of worms nightmare.

    The old light switch must have been around 40 years old, and did not have a spot for a ground wire. The new occupancy sensor would need a ground wire so I ran one from the main panel to where the light switch/occupancy sensor would be. So far so good.

    At the downstairs light switch the old knob and tube was run through conduit from the ceiling to the light switch box. I had to remove the conduit to run the ground wire through the conduit to the switch box. By the time I had the conduit replaced with the new ground wire, it was getting late and dark outside so I figured I’d clean up and finish installing the occupancy sensor the next day. I reinstalled the old light switch, taped up the ground wire and tucked it aside, and turned the power back on. Everything seemed normal but then around 10 minutes later the circuit breaker surprisingly shut off. I left it off until I could look at everything closer the next morning.

    When I looked at it the next morning I found bad insulation on the old knob and tube, which is normal for wire this old when it's moved around, so I figured it was a good time to replace the wire with some new 12/2. I installed a junction box near the top of the conduit because I would not be able to replace the old wiring going to the light fixture (it was run on top of the heater duct).

    I replaced the old knob and tube from the basement light switch with new wire run inside the conduit, and was ready to start wiring everything back up when to my surprise I found that the hot wire (knob and tube from upstairs, acting as a feed wire to this basement light switch) was also shorted between the heater duct and the floorboard. When they originally wired this house they ran the wires between the floorboards and the heater ducts. It would be a nightmare to try and fix the short, and besides, it was another chance to replace some more knob and tube with some new wire.

    Just for reference (as far as I know) this branch of the circuit runs from the main fuse box to a bedroom light on the main floor, and from there it goes to the bathroom light and then to a hallway light, and finally back downstairs to the light switch that I was replacing.

    I would only need around 6 feet of wire from the upstairs hallway light switch to the junction box downstairs (luckily the upstairs hallway light switch is right above the basement light switch). I removed the old knob and tube and ran new 12/2 from the upstairs hallway light switch to the junction box downstairs.

    So basically all the old knob and tube from the hallway light switch to the junction box, and from the junction box to the basement light switch was now all new wire. The only knob and tube that was left untouched was in the bedroom light and the bathroom light (I’ll replace those later) and from the junction box to the light fixture. All the wiring was pretty straight forward. I connected everything together, flipped on the circuit breaker, and heard the freezer kick back on.

    The lightbulbs in the bedroom and the bathroom were removed when I was tracing down the short in the old knob and tube, but I figured that with those lightbulbs removed that it shouldn’t matter for the basement light, and the basement light should still work on its own. To my surprise neither the basement light or the hallway light would work. I quickly shut the breaker off and looked over everything again.

    All the connections looked good, so I replaced the lightbulbs in the bedroom and the bathroom and flipped the circuit breaker on again. This time the basement light and the hallway light still didn’t work, but the bathroom light did work. Here’s where it starts to get weird. The bedroom light uses two bulbs, one was on, the other was off, and the bedroom light dimmer would not dim. I shut the circuit breaker back off because nothing was making any sense.

    All I did was replace one old knob and tube wire from the hallway switch to the basement light switch. Why would all of these bizarre things be happening now? I suppose it could be from a bad dimmer switch, but wouldn’t that just effect the one light? There is no neutral wire in the light switch boxes, just black hot wires, so how can I check for power at the switch with my meter? What is the best way to trace down this bizarre problem?

  2. #2
    Join Date
    Jun 2007
    Location
    Fayette County, Ohio
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    5,558

    Default Re: Completely Perplexed.

    One of the problems with K&T wiring is that there is often side feeds hidden. Did you pull all the old out or just run new? Where the switches wired to swith hot or neutral both ways often exist in K&T wiring.

    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  3. #3
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    Apr 2012
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    Question Re: Completely Perplexed.

    Quote Originally Posted by JLMCDANIEL View Post
    One of the problems with K&T wiring is that there is often side feeds hidden. Did you pull all the old out or just run new?
    THANKS for your help Jack

    Where it was coming through the floor/basement ceiling I cut it and pulled it out. From the floor it ran up the side of the wall with two of those round ceramic insulators to the switch. I capped both ends and left that section in the wall.


    Where the switches wired to swith hot or neutral both ways often exist in K&T wiring.

    There are no neutrals in sight. All you see are the hots.

    I think I found the problem. When I was running my new wire through the floor I saw another old K&T wire laying between the floor and the heater ducting. I went downstairs to see where it was coming from or going to, but it could not be seen, so I left it alone. There was also an extra hole inside the wall right next to where the other wire was located. When I first saw it I thought "how odd" that the builder would drill a hole like that for no reason.

    Well tonight I took a closer look at this mystery wire and to my surprise it was shredded at the end. I cannot find where the other end of it is, or where it runs to, but tomorrow I will cut a bigger section of the floor out to see if I can learn more. I don't know if this wire has anything to do with the extra hole that I saw. If this wire was at one time run through that hole, then the other half of the wire should still be inside the wall, but the only other wire in the wall is the wire that runs up to the light fixture. I verified this with my meter.

    My best educated guess right now is that the wire must be the neutral for both the basement and hall light, which would explain why those two lights don't work. If that's the case then I can't imagine how it got cut, but for right now that's the best explanation for why those lights no longer work.

    Tomorrow I will test to see if the end of the wire that I can see goes to either the hallway or basement light fixtures. I don't believe in splicing or repairing K&T wiring, so whatever this wire used to be for will have to be replaced. If it is the neutral wire, then how could the bathroom and bedroom light still work? Could they have possibly run a separate neutral wire to those rooms?

  4. #4
    Join Date
    Dec 2007
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    Tennessee
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    Default Re: Completely Perplexed.

    No neutrals and two hots, that would be for a 240 VAC circuit. A 120VAC has one hot and one neutral. If you are relying on the color of the insulation on the old wiring, don't. You have to use a meter to determine which is hot and which is the return.

  5. #5
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    Apr 2012
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    Post Re: Completely Perplexed.

    Quote Originally Posted by keith3267 View Post
    No neutrals and two hots, that would be for a 240 VAC circuit.
    I'm sorry I must have used the wrong terminology. When I said 'two hots' I meant the main hot coming from the service panel and going to the one side of the light switch, and the "hot" on the other side of the switch, going up to the light fixture (one hot split by the switch). All the neutrals must be in the ceiling run from one light fixture to another.

    Right now the bedroom lighting, hallway lighting, bathroom lighting and basement lighting are all on one circuit breaker. Ultimately I would like to change that and have the hallway and basement light on a separate circuit breaker, along with having a separate breaker for the bathroom light/fan, and another separate breaker for the bedroom light. Another way would be to have the bedroom, hallway and basement light on one breaker, and the bathroom light/fan on a second breaker, but I've never run multiple rooms like that and I can't find any information anywhere on how to do it, so the separate breakers seems better to me. What is stopping me is this old K&T wiring.

    I can't seem to trace down how the neutrals are run. Is the only way to find where the neutrals go to by disconnecting one neutral at a time at the main service panel, and see which neutral(s) effect which lights? I do have a wire tracer but it's not showing anything at the service panel when I send a signal from those rooms.

  6. #6
    Join Date
    Jan 2011
    Location
    Columbiana, Alabama
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    623

    Default Re: Completely Perplexed.

    It's hard to follow what's going on (been on jobs) but tracing K & T gets a lot easier if you tie a single conductor to the neutral in your panel for testing, even if it's 40 ft long.

    Also, don't rely on a neon test lamp. Get a tester that imposes a load on the circuit, offers a continuity function such as an Ideal or Greenlee, both available at Home Depot, etc.

    Also, some inexpensive occupancy sensors don't have a neutral connection but rely on the green or bare ground to function. They have a UL listing, but are frowned upon by inspectors, may not control light loads such as LED's or CFL's and were partly responsible for the new Code requirement that all switch locations must now have a neutral in the box, even if it's not needed at the time.
    Good Luck from Columbiana, Alabama
    Maurice Turgeon, Hidden Content

  7. #7
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    Tennessee
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    Default Re: Completely Perplexed.

    I don't know why I am having a hard time following your explanation here. Have you removed the light fixtures to look at the wiring inside them? Did I understand you correctly that you replaced all the wiring between two switches because there should be no wiring that goes between two switches unless it is where one light is controlled by two switches.

    This is just a guess here because you are dealing with old wiring, but the original electrician probably ran wire pairs to each fixture in a daisy chain from the CB (or fuse at that time). Then at each fixture, instead of hooking up the hot, he ran a pair of black insulated wires to the switch box and connected them to the switch. Now the hot in the fixture box is connected to one of these black wires to the switch and the returning wire from the switch is connected to the light fixture along with another hot wire to the next fixture.

    If you are replacing the wiring to the switches, you need to replace all the wires between the fixture and the switch.

  8. #8
    Join Date
    Apr 2012
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    Smile Re: Completely Perplexed.

    Quote Originally Posted by keith3267 View Post
    Have you removed the light fixtures to look at the wiring inside them?
    Not yet. Was using a meter to trace wiring down via the light socket.

    Did I understand you correctly that you replaced all the wiring between two switches because there should be no wiring that goes between two switches unless it is where one light is controlled by two switches.
    Yes, that's correct. That is what is not making any sense to me, and why this has become so frustrating. The hallway light (upstairs) has the hot run from the fixture to one side of the switch. From the other side of the switch it runs directly downstairs to one side of the basement light switch. From the other side of the basement light switch it runs to hot of the basement light fixture. So how is it getting hot from the circuit breaker? This is what makes no sense to me and I don't see how it could have ever worked, BUT I did read that back then they used to fuse the neutrals and use them the way we use hots today. I'd like to learn what they did for future reference, but I may never know how they wired it.

    If you are replacing the wiring to the switches, you need to replace all the wires between the fixture and the switch.
    Yes, I'm wasting too much time trying to figure out what they did, and eventually I would need to remove all of this K&T anyway and update everything, so I'm focusing on the best way to do that. Right now there are 4 lights (bedroom, hallway, bathroom and basement) lights and one receptacle (basement freezer) on this circuit breaker. I think it's best to put the bathroom light/fan and bathroom heated floor on it's own breaker, and then put the hallway light, bedroom light and a bedroom receptacle on a separate breaker. The hallway light switch and bedroom receptacle are on the same wall so that should make it easier to run wires. There is only one light in the basement now. I would add a couple more and put all of the basement lights on a separate circuit breaker too. Does this sound like a good way to update/modernize things?

  9. #9
    Join Date
    Dec 2007
    Location
    Tennessee
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    Default Re: Completely Perplexed.

    OK, I think I see what they did. They daisy chained the neutrals through the light boxes and receptacle boxes. They daisy chained the hots through the receptacle boxes and the light switches, but not through the light boxes. They would run a pigtail from the cold side (when off) of the switch to the light box. That probably used the least amount of copper.

    To get everything working, you have to make sure the hot sides of the switches are daisy chained together and the pig tails are on the cold side of the switches. If you hook up the hot wire that daisy chains to the switches and receptacles downstream, then whenever that switch is off, so is everything downstream.

    Because you are changing your wiring, I'm guessing that this will be a major code violation. The semi-retired electrician will probably pipe in on this, but he may have the best solution for your situation right now that does not violate the codes.

  10. #10
    Join Date
    Jan 2011
    Location
    Columbiana, Alabama
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    623

    Default Re: Completely Perplexed.

    I believe you made a wise decision to forget how they did it and concentrate on how it should be done.

    Because you have some existing lights and receptacles let me just list some does and dont's:

    1)Each bath should have it's own 20A circuit and the receptacle should be GFCI protected. There are exceptions if you have two baths with only the receptacles on the 20A circuit.

    2)The heated floor will probably require a 120V 20A circuit and possibly a 240V 20A or even 30A circuit. Don't load up the circuit to more than 80% of the breakers size.

    3)Limit the number of lights or receptacles to no more than twelve on a 20A circuit. Generally, AFCI breakers are required in all areas that do not require GFCI protection. When in doubt install them, they're designed to offer superior wiring protection and some shock protection as well.

    4)If the basement is unfinished all outlets must be GFCI protected.

    5)Be sure to route the feed from the breaker to the switch (new Code) then to the light. Unless you have an occupancy sensor the switch will not use the white so just connect the whites together so the light will have a neutral.
    Good Luck from Columbiana, Alabama
    Maurice Turgeon, Hidden Content

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