knob & tube wiring

TrevJo · 06-05-2005, 05:16 PM

I removed an old light fixture in a house I am renting to put on one that a cover can be attached to. The wiring is unfortunately knob and tube and now that the old fixture is off I can't tell which wire is hot and which one is neutral. Every website says that hot is black and neutral is white, but these ones aren't colored. Is there another way that I can tell which one is the hot wire and which one is neutral? What would happen if I hooked up a light bulb and got the hot/neutral backwards?
Alternatively, if I give up on the fixture (it's useful but not necessary), what steps do I need to take to insulate the wires so that they are not a hazard, before I turn the breaker back on? The wires are only about 1½" apart.

Thanks in advance!

MinConst · 06-05-2005, 08:51 PM

TrevJo,
If you have one of those two wire bulb testers you can find the hot side of the pair. This may sound strange but if done as described it is safe. Normally you would touch both leads from the tester, one to each wire. This tells you there is power if the bulb lights. It will light brightly. Now to find the hot side. And please read this carefully. Hold the black lead (metal probe) on the tester in one hand. TOUCH NOTHING ELSE. Then touch the red lead of the tester to ONE of the wires. BE very careful not to allow the wire to touch anthing else or the lead of the tester to touch anything else. If you have the hot side you will get a slight glow of the testers bulb. You will not feal anything. If you don't get a light try the other wire. One will give you a slight glow of the bulb. Of course the power must be turned on for this to work. Please be very careful and don't allow the wires to contact each other or anything else. You can spread them apart so they remain free from touching anything or each other.
For your second question. If these wires are in a box, you can put a wire nut on each wire. Tape each wire nut, with electrical tape, so it can't fall off and place the wires in the box. Put a blank cover on the box. If the wires are not in a box, you should add a box to house the wires. Or disconnect the wires from the other end.
I hope this help. Let us know how you make out.

jproffer · 06-06-2005, 09:37 AM

In this case it doesn't sound like you're remodeling or doing any other major project, but just FYI for anyone else who happens along that is doing something more, here's something to check out:

In my area, if you remodel/renovate/rebuild more than 15%(I think thats the magical number) of the value of the home, you are required to update everything to current code. In this case it would mean the K&T had to go, all of it. As well as any plumbing that wasn't up to par.

TrevJo · 06-08-2005, 03:14 AM

Thanks everyone. The conclusion I reached from talking to an EE friend of mine was that it wasn't necessary to find out which was hot and which was neutral for a simple lamp fixture. So, I hooked it up and it is working.

As far as updating to code goes, that is good to know. Since I am renting, I'll make sure not to get to that number.

I just have two identical fixtures I want to update. My girlfriend owns a house though and also has K&T and is considering similar work so I'll make sure she knows.