Thankfully, I have never seen any knob and tube wiring.
I did read that knob and tube does not always use standard switching
so caution is advised.
This site says...
There are a few things you need to consider when dealing with knob &
tube wiring. The first thing is they can be very brittle and the
insulation can start falling off exposing bare conductors. The second
thing to consider is how 3-way switches were once wired. At one time
when houses were wired with knob & tube, they would feed the 3-way
switches with a hot and neutral. They would then send a single
conductor from the point screw of the switches to the light(s). The
switched would either send up a neutral signal or a hot signal
depending on the position of the switch. This is often called lazy
susan switching. If the lazy susan wiring gets changed around on the
3-way switches you end up with a short circuit (hot to neutral short).
Since it does not sound like you have this issue you probably don't
have lazy susan wiring.
Since I have never messed with any knob and tube I really can't tell
you what would happen. I would not want to risk putting a direct
short on brittle insulation.
One way you could tell if you do have a hot and a neutral at the
3-ways would be to turn the power off and disconnect both switches.
Then with the power on, check between each wires of each switch. You
should NOT have 120V between any of the wires. If you do, then you
might have one of the above switching arrangements. (Stop here and
If you don't have 120V between the wires, you could then go one step
farther to make sure you do have travelers. Turn the power back off,
and with a helper do a continuity check. The two wires that were not
hot should go directly to the other switch. If this is the case then
it is a safe bet that you do have a standard switching arrangement.
On Sat, 26 Jan 2008 16:00:22 -0500, "BETA-32"
There weren't many codes when knob and tube wiring was installed. Generally
if it hasn't been messed with it is probably safe since it's been in use for
many years, but you do need to be aware and not overload things.
As for 'standard switching' the one thing I've seen when I've dealt with it
is that they didn't always keep the hot and neutral together. That is, the
hot might run thru the switch box and on to the light or whatever is
controlled, whereas the neutral might come into the light from another
I've never heard of "lazy Susan" but it goes by many names, typically
"Carter system, or lazy neutral", and although pretty much outlawed by the
NEC in 1920, it was used for decades longer and not exclusive to K&T wiring.
From my experience K&T wiring has held up better than anything in the
industry until thermoplastic came on the market. It's demise came when
circuits were required to be grounded. In switch boxes, it tends to be in
excellent condition, but in ceiling outlets where light fixtures were in
close proximity to it, it would bake the insulation causing it to crumble
when moved. The rubber covered cloth conductors used in the forties and
fifties were even worse in this situation
Well, no luck for me. I must have a bigger problem than I realized. I did
the steps below, but with the power ON, none of the wires are hot -- not hot
when I put the tester from each wire to each other wire, and not hot when I
put the tester from each wire to the metal switch boxes.
It hasn't worked since I bought the house a long time ago, so something else
must be wrong somewhere. I have knob and tube wiring.
Because knob and tube is not grounded, the wires might be hot and your
don't have a tester that will sense it.
Try one of these. Test it by putting in in a known hot outlet before
On Mon, 28 Jan 2008 18:14:45 -0500, "BETA-32"
Thanks again. I tried that and it didn't work. I connected the wire to a
metal cold water pipe near each of the switches and tried using that as the
second wire for the test. So, something else is apparently goofed up
somewhere. I'm going to buy one of those voltage testers today and see if I
have any luck with that. I doubt it, but it's worth a try.
use a 25 watt light bulb never a digital VOM it will give you unusable
readings by capitance coupling.
The type of device I am going to buy is like the one in this link, I think:
I'm guessing it's not really a volt meter. Instead, I think it is a device
that you touch to one wire (not two) to see if it is "hot". I'm not sure
that type of device could work by touching a wire that no current is flowing
through, but I saw a heater guy using one (he was in love with it) and he
claimed that even with no current flowing, it can tell of the wire is a hot
wire or a ground. Beats me, but for around 15 bucks I'll have a new toy, so
I'm going to try it.
You are correct, it detects voltage and will detect a "hot" wire. You
don't need current flow in the wire - there will be voltage with or
without current. ("Indicates live current" in the description is
technical illiteracy.) Real handy for K&T. It is non-contact - you just
touch the outside of the wire insulation. Neon test lights can also be
used but require contact.
Well, I bought the toy and it works great. But, in my case, none of the
wires that go to either 3-way switch are "hot". Same for the wires to the
actual hallway light. So, there must be a broken wire or bad connection
somewhere else in the circuit.
That sounds right. If you can see the wiring from the attic or
basement would be the next place to go for clues.
Trying to re feed the switch from another circuit sounds like the only
way to continue.
Do each 3-ways have only 3 wires? Does it look like wiring has been
removed from any of the boxes?
I will be heading for the attic in a day or two, especially now that I have
Both 3-ways have only 3 wires and it doesn't look like any wiring was
removed from either one. It all looks like the dusty old original wiring,
and the switches I took out and replaced look like they were the original
switches -- ancient.
Attic and basement are real good ideas. Your new toy should be a big help.
If you get stuck, another method of attack is check continuity between
possible ends of wires to see what the actual wiring is. Include the
light sockets. (I would also verify the socket screwshell connects to
the neutral.) When measuring continuity you have to watch there is not
voltage between the wires. If you don't have a good understanding of
3-way and 4-way switches (one of the switches was 4-way?) this method
may not help. If you work out what the wiring is you can determine which
wire should be the hot feed and trace it. K&T wiring problems can be a
Thanks. A long time ago, I did use a continuity checker and tagged each of
the 3 wires for each 3-way switch and the two wires for the light fixture.
I have them numbered so that #1 on one end is directly connected to #1 on
the other end, etc. Of course, after I did that, I had no idea what to do
with the information.
And, no, there are no 4-way switches -- just two 3-way switches.
There are 2 ways a 3-way might be connected with K&T. In both, 2 wires
go between the 3-way switches. And at one end the 3rd wire goes to the
light socket connection to the end of the light bulbs.
=================In one way of wiring, the 3rd wire at the other switch goes to the other
(screwshell) terminal at the light sockets. This is not a good way to
wire a light.
=================The other (more likely and preferred) way of wiring a 3-way, the other
wire at the 2nd switch does not connect to the light socket. **This will
be the hot feed to trace.
(With both wiring methods the 2 wires between the switches connect to
the same-colored terminals on the 3-way switches.)
=====================Don't know if you noticed - Terry started a 2nd thread on this 2-1.
Thanks. I'll have to check this out a little more on Tuesday. Between now
and then I won't be home while it's daylight outside when I can see
everything with and without the power on.
I went into the attic this morning, and part of the floor is already up from
when I was working on it before. But I have to take another board up to
access above the light, and I didn't have time to do that today.
I didn't see the other thread that Terry started on this, but I'll go there
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