Replies

1. 
   Guest_ | Jan 18, 2000 02:03am | #1

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   More information??

2. 
   CAP_ | Jan 18, 2000 04:44am | #2

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   Pmor--

   Old building wiring, especially knob-and-tube, can be a real challenge to trace. Here are some tips:

   -- usually a neutral served more than one circuit. This is called a shared or common neutral. This is important, safety-wise. You may have killed power to the circuit that you're working on, checked the hot to neutral volage and confirmed no power, only to have the neutral conductor go hot! That's because a light or appliance was turned on in a circuit that shares the neutral with the one you're working on. One way around this is to shut off power to the whole building in which you're working.

   --The hot and neutral conductors don't run parallel. The neutral (which is identified as such only at the outlets) will zig-zag all over the attic or basement, with the neutrals of fixtures and outlets tap-spliced onto it.

   --As for your switch, you may have a switch leg--a hot conductor coming into a switch box and a switched conductor going to the light fixture. No neutral.

   To trace the hot conductors, get a toner-tracer set like phone men use. Makes it a snap. Costs about $80. OR, you could shut off all power, open up the boxes, and start checking continuity. Two people and long test leads are a plus if you take this route; I don't recommend it.

   A very good resource if you working on old wiring is Shapiro's "Old Electrical Wiring", available from Amazon and others. It's like being at a convention of helpful, hundred-year old electricians. The section on troubleshooting is excellent.

   Just be aware that, as Shapiro points out, working on old wiring presents a whole different set of hazards than modern wiring.

3. 
   Guest_ | Jan 18, 2000 04:58am | #3

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   Since Knob & Tube wiring uses a seperate Hot and Neutral wire and they need to be routed with air between them, the routing used back then followed very different rules than those we follow today.

   You may find that one neutral wire winds around from several fixtures in one manner, while the hot may have come from somewhere else. Also take care because they used to fuse both Hot AND Neutral back then (if those wires have been installed to an updated box at any time they may be crossed, or two circuits may share one Neutral, and so on). Because we have had 60+ years of additions & revisions what you are looking at today may be crazy and make no good sense. In fact, assume that. You'll be better off.

   Hints:

   1) Make SURE the hot is fused and the neutral is not (if you turn off the breaker / fuse and the light goes dark that does NOT prove that the power has been turned off, you may have only broken the Neutral leaving all 120V waiting for a ground (you)). Test the wires with a proper tester first - GB makes a nice little 'tingler' that senses the alternating current and will tell you (by beeping) if the wires are hot. The fixture need not be turned on for this to work.

   2) Make sure that only one breaker / fuse are connected to any one circuit. Use the above-mentioned tester. These testers can be fooled into thinking that a wire is hot if a neighboring wire is hot (they can sense AC over about 5 - 10 inches of free air). When in doubt, use a voltmeter and a trusted ground. The tinglers (or whatever they are called) are alot more easilly fooled arount K & T than around modern wire, I think it is the close proximity of the ground lead in the modern or something like that.

   3) Try to trace back from your box to the fixture to answer your question.

   More Warnings about K & T:
   1) The connections may not be in boxes or accessible (it was common to bury then in the wall with no access) - so you won't know when the line is spliced off in other directions. Very un-code these days.

   2) Those connections will be made with solder and tape (yuck, probably secure but who's to know - remember that fires are started by HEAT. No matter how little you use that wire all 15Amps will be available to make heat when a joint gets sorta loose (imagine expanding and contracting with every heat / cool cycle for dozens of years, or any other way that that wire might have been disturbed over that time). A modern joint, enclosed in a modern fixture box will protect your house, the other is an unknown).

   For all of the above reasons, and also for peace of mind, when you want to change a circuit made up of K & T replace the whole circuit with modern cable. You decide the wire routing. You (or your electrician) confirm that there are no loose ends (literally) or electrocution hazards hiding in your walls. You can clean up that awful mess a lot easier than you thought - especially in the basement where all the wires are exposed - by ripping it out and redoing it.

   If you really want to save yourself aggravation and worry replace it with modern.

   If you think it is not possible to route new wiring where you want to, go look for someone with old-house restoration experience you might be suprised what a skilled electrician can do for you here.

   One idea if you really want to keep a K & T circuit but are now worried because of all I just mentioned about 100 year old wiring:

   Install a very small fuse on that circuit.

   Here's what I did for one that could not be replaced but was worried about a 'someday' fire hazard from the old stuff: The smallest breaker available for that fusebox was 15A, and I only had two lights on the old circuit (so I only needed about 120W total power). I added a small box on the side of the fusebox and installed a 1.5A fuse in series with the Hot. These little fuses are used to protect electric motors and are available in pretty small sizes. Now, the maximum Heat that circuit could make was 1.5A x 110V = 165Watts. Still darn hot, but better off than 1650 Watts the other way.

   Don't ask me how it worked out in the long run, cause I figured out how to replace that last circuit and now its gone. But figured I'd pass the idea along in case any one else wants to try it.

   According to those that track these sort of things, most fires are caused by open flame (fireplace, cigarette, etc). Then by appliances and frayed cords. Then by outlet or switch fixtures that are improperly installed or damaged. Last of all (electrically speaking) by the wires in the walls themselves. So maybe I worry too much about the old wires. :-)

1. 
   Guest_ | Jan 20, 2000 02:56am | #4

   *Frequently with K & T the neutral to a light is switched, rather than the hot leg. This can get confusing, especially with a switched-neutral 3-way! Lee

4. 
   Pmor | Jan 20, 2000 03:01am | #5

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   I'm looking for a resource to help me to isolate old wiring circuits without cutting off power to other parts of the house - I'm trying to isolate a basement circuit but I can't seem to find a hot lead. The best I can find is a black wire coming from a switch and a white wirre that disappears somwhere upstairs. I can usually find my way around circuits quite well, bu this one has me stumped.