+ Reply to Thread
Results 1 to 10 of 18

Hybrid View

  1. #1
    Join Date
    Apr 2012
    Posts
    212

    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
    Posts
    5,942

    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
    Join Date
    Apr 2012
    Posts
    212

    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
    Location
    Tennessee
    Posts
    1,908

    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
    Join Date
    Apr 2012
    Posts
    212

    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
    Posts
    794

    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
    Join Date
    Apr 2012
    Posts
    212

    Smile Re: Completely Perplexed.

    Oh my god, I just figured out that our 1875 watt hair dryer is 15.62 amps

    Time to upgrade that outlet to 20 amps....

  8. #8
    Join Date
    Jan 2011
    Location
    Columbiana, Alabama
    Posts
    794

    Default Re: Completely Perplexed.

    Quote Originally Posted by MyMilan View Post
    Oh my god, I just figured out that our 1875 watt hair dryer is 15.62 amps

    Time to upgrade that outlet to 20 amps....
    True, the only reason you haven't had tripped a breaker is because the 15A breaker can run in an overloaded condition for several minutes without tripping.

    Short term it would be better to get a smaller hair dryer until you run a 20A circuit.

    Yes, you can use the floor heater circuit, if it's 120V and only pulls 1A, to power your hall and bath lights.

    You can call your power company engineering dept. they will be able to tell you the short circuit available current to your home. Chances are it's well below the 10Kaic number you need to worry about. The answer will be free and if it's too high it's better to know sooner than later.
    Good Luck from Columbiana, Alabama
    Maurice Turgeon, Hidden Content

  9. #9
    Join Date
    Apr 2012
    Posts
    212

    Question Re: Completely Perplexed.

    Quote Originally Posted by The Semi-Retired Electric View Post
    Short term it would be better to get a smaller hair dryer until you run a 20A circuit.
    Luckily it has a lower fan speed option that I will use. Was really surprised to see how many amps it was pulling. Because of this I have decided to run 12/2 for all the new main floor recepticle wiring. I will only use 14/2 for lighting. The only exception will be the living room lighting because one day I plan to install a fan in there, so I'll run 12/2 for those lights.

    Chances are it's well below the 10Kaic number you need to worry about.
    So I want a lower number?

    What does this number tell me about my house wiring?

  10. #10
    Join Date
    Jan 2011
    Location
    Columbiana, Alabama
    Posts
    794

    Default Re: Completely Perplexed.

    Quote Originally Posted by MyMilan View Post
    Luckily it has a lower fan speed option that I will use. Was really surprised to see how many amps it was pulling. Because of this I have decided to run 12/2 for all the new main floor recepticle wiring. I will only use 14/2 for lighting. The only exception will be the living room lighting because one day I plan to install a fan in there, so I'll run 12/2 for those lights.


    So I want a lower number?

    What does this number tell me about my house wiring?
    Yes the lower setting would solve the problem short term.

    I carry #14 wire but have not used any for years. True it's easier to wire and box fill is less of a problem but you're limited to about 10 receptacles (or lights) with 15A (#14 wire) so you would have 20% more "home runs" and now that we have to install $45 AFCI's (15A & 20A cost the same) so IMO there is no good reason to use #14 anymore.
    Good Luck from Columbiana, Alabama
    Maurice Turgeon, Hidden Content

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •