knob & tube question

Discussion in 'Electrical Forum discussion & Blog' started by Master Brian, Feb 10, 2009.

  1. Master Brian

    Master Brian DIY Senior Member

    Messages:
    368
    Location:
    Kansas
    As far as I know, I only have 2 knob and tube circuits left in my house. One controls the bedroom lights and one controls the dining/kitchen/living rooms.

    I want to unhook the circuit for the bedrooms, so that I may get rid of it. I'm not ready to unhook the circuit for the other 3 rooms.

    I know which hot wire feeds each circuit, what I am not sure of is if both circuits share a neutral. Was that common in 1915 or not? It may become clear once I go back into the panel, but if not, is there an easy way to test if it is a "live" neutral?
  2. Chris75

    Chris75 Electrician

    Messages:
    608
    Location:
    Litchfield, CT
    Trace out everything before you just start cutting stuff.... I wasnt around in 1915, so not sure what common was.
  3. Billy_Bob

    Billy_Bob In the Trades

    Messages:
    422
    I don't know if I should answer this question or not???

    If testing for this type of thing and doing the testing properly - knowing what you are doing, then you can determine if the neutral is connected or not.

    But if you don't know what exactly is going on with this testing, then quite easy to mess up your wiring, electrocute yourself, or damage your test equipment.

    Basically all neutrals connect together at the main panel. So if measuring voltage from a hot from another outlet to any neutral which is connected, you would get a voltage.

    Or if the MAIN POWER was turned off, and you were using a continuity tester or an ohm meter, and measuring from another neutral to this neutral, and it was connected, then you would get a reading. (Using meters for these tests with the power on can damage the meters.)

    The problem is this is a "circuit" with possibly many things interconnecting. One light bulb on this neutral and the switch on would connect the neutral to a hot. Then that hot may travel to another "on" electrical device and "see" a neutral from that device. So in testing, the neutral may appear to be connected, but only may be connected via the light bulb and hot (after you had disconnected the neutral). So its necessary to fully understand your readings and what is going on with the wiring - what all is connected to what.

    Then with K&T, the wires are the same colors. So you need to determine which is hot and which is neutral.

    So before working on K&T, you should have a full understanding of how to use a multi-meter and how this meter can be damaged if not used properly. A full understanding of K&T wiring and what possible connections may exist. And a full understanding of electrical circuits and how to trace out circuits.

    Basically this is advanced stuff.

    The easy way to do this is to cut holes in the walls and see what wires are going where and if any wires are spliced in the walls, then heading off somewhere from there.

    Then what goes in, and what comes out! -> If you go up in the attic and there are two wires going down a wall. And on that wall below there is one wall switch. And you remove that wall switch and inside the box there are two wires as well (and no other electrical boxes on that wall), then it would be logical to assume that those wires only go to that switch. But don't bet your life on it! You might tear out the wall or cut a hole in the wall and see wires spliced to those wires in the wall!

    I saw this recently twice! A short run of K&T of about 6 ft. from a wall switch to a bathroom wall light fixture. Should be just two wires running to the light fixture right? Nope... In the ceiling there was a splice into the wires and another wire leading off a few feet and then cut and taped. Then in the wall there were two old twisted lamp cords spliced into the same wire and these were leading off to either side of the light fixture, then cut and taped.

    So at one time a ceiling fixture was installed and then removed. Then there were wall sconces installed and then removed. Wires left in ceiling/wall.

    So no telling who did what at any time in the past.

    Tools for testing are...

    Turning everything on/off to see what is on a particular wire run. Disconnecting the wiring at a certain point and see what no longer works.

    Using a voltmeter.

    Using a continuity tester.

    Using an ohm meter.

    Using an inductive wire tracer with signal generator...
    http://www.professionalequipment.com/extech-tone-generator-amplifier-probe-kit-40180/wire-tracer/

    Testing from the hot of another circuit with a long length of wire.

    Testing from the neutral of another circuit with a long length of wire.

    Visually tracing wires.

    Cutting holes in walls/ceilings and using mirrors/flashlights to see what is in there.

    Removing switches/outlets/fixtures and seeing how many wires are in the box.

    Disconnecting a wire at both ends and measuring for ohms/continuity.

    Or rip out all the walls and ceilings!
    Last edited: Feb 11, 2009
  4. Billy_Bob

    Billy_Bob In the Trades

    Messages:
    422
    P.S. I might add that it is quite easy when doing the above types of testing to get carried away with what goes where, be on the track of finding where something goes, then forget that you had turned the main power back on for the previous test. Then Zap!

    So always double check that the power is off, then verify it is in fact off. Have a lamp or radio on and be sure these things are off.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,263
    Location:
    Cave Creek, Arizona
    neutral

    What is a "live neutral"? If the neutral is shared with a second circuit, AND they are not opposite legs of the 240 main, then it can be overloaded. One way to tell is to disconnect the neutral at the main panel and see what no longer works. The reconnect it and pull the fuse on the circuit and see if the same items are out of service. If some are not, then they are on a separate circuit. ALSO, if anything burns out with the neutral disconnected, it will be because there are two interconnected legs and the devices got zapped with 240 volts.
  6. Master Brian

    Master Brian DIY Senior Member

    Messages:
    368
    Location:
    Kansas
    Without knowing all the correct lingo, what I meant by "live" neutral was a neutral wire basically feeding two circuits.

    Typically if you unhook and take away the hot wire and leave the neutral, all you'd end up with is basically a "ground" wire left, so no harm should be able to come of it. i.e. There wouldn't be any way for current to flow through the wire, so it wouldn't pose any safety concerns. Correct?

    What I am worried about is that the neutral might still be connected to another circuit, thereby it could become energized when a receptacle or switch becomes "active".

    I hope that makes sense, again I appologize, I can't always get the correct termanology.....

    Billy-Bob, thanks for the feedback. I thought about the continuity test, it'd just require a decent lenght of wire, shouldn't be a big problem to come by. The volt test with a working outlet is a good idea as well. I will admit I know how to run the tests, but I don't always feel very safe doing them, because I do realize the potential danger.

    I am almost certain that the neutrals are shared on the circuits, so I'm heavily weighing the option of just killing both circuit and prepairing both for new wiring at the same time. Accessing the old K&T wiring to trace it is tough, opening access panels for new wires is relatively easy.

    Thanks for the feedback.
  7. Master Brian

    Master Brian DIY Senior Member

    Messages:
    368
    Location:
    Kansas
    That's virtually impossible to do without gutting the plaster off the walls. You've never seen my house, but I'd bet your guess would be as good as mine! It's like Billy Bob said, stuff can be run from anywhere.

    The good part is I know it's only these two circuits that are left as K&T and for the most part it is only for lighting. The reason's for unhooking and having new re-ran is that I want to install new lighting and some of these are buried under insulation, which is normally not allowed with K&T.
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