knob and tube

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electricalist

electricalist

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dallas tx
what is the single wire in the attic that connect one light to the next? Hot or neutral. What is the other single wire that is going to the switch? Hot or neutral. All the single wires from light to light in the attic were tied to black on the fixture. Is this a switched neutral
 
From somewhere else in the attic thete is a single wirr it goes through a tube and splits into 2 wires . One goes around a knob then another knob and ties into the black one a light fixture . The white from that same fixture runs un interrupted down to a switch. Where the wire split into 2 the other wire ggoes through a tube splits into 2 and one goes through a knob then another then ties into the black on the light fixture. The white from that light fixture ties to another single wire going down to a switch . This is repeated through another light. The switches, 2 were 3 ways but made up a little weird. When I took them out I thought this is strange like they were fed backwards. But the wires were brittle and looked bad. I showed the home owner and put it back. It looks fairly easy to remove and replace it all but what was. Im really not sure. If I had a ground I think id figure out what was what but thats not why I was there.
 
Get a non-contact voltage tester for knob & tube. Make sure the lights are off, then you can at least see which one is hot. Obviously you'll want to use your regular meter or wiggie to make sure you've turned the circuit off before you work on it, but the preliminary test really helps.

And yes, very often they switched the neutral for k&t lighting circuits.
 
That allowed them to use shorter distance of hot wire to feed all of the lights and run the more complicated path to each switch using the neutral wire which did not need as careful handling. The idea of keeping supply and return together was not critical because no ferrous raceways were used. Maybe not even ferrous boxes for panels.
 
Thanks Jay and Gold I was using my non contact v tester when I first got in the attic and looked around. Ive learned they are only used for when I wonder how dead is something . I used it as I was trying to see whats going on. It was hot to the black when the switch was on but then hot to the white when it was off. Hell the 3 way might have been upside down and across the switch as single pole. . I may be crazy but it seemed like they used the 3 way as a way to open and close the neutral and still feed the other switch a neutral. I was really close to running my extension cord all the way to the panel outside and reference the neutral/ground at the panel.
 
If you have three ways that seem rather strange it may be something similar to the schematic shown here.

That is first schematic I found after searching for "California 3 way". Is not exactly what you have but same basic concept if you have what I suspect you may have.
 
It could not be most of the circuits in that thread since we know that a constant hot goes to all light sockets and I suspect that the lights are not all switched at once.
 
electricalist said:
. . I may be crazy but it seemed like they used the 3 way as a way to open and close the neutral and still feed the other switch a neutral. I was really close to running my extension cord all the way to the panel outside and reference the neutral/ground at the panel.
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This is a really good idea, when the K&T is new, and you are still learning about all the variations that were done back in the first half if the
1900s. Bringing a "known ground" to the wiring in question (one of the conductors in your extension cord) will do wonders. Leave the power on at the overcurrent protective device (OCPD), remove the light bulbs and turn the switches off (if they are single pole) and then test for the hot with a voltmeter, AND then, after knowing where the hot is, turn the power off at the OCPD and check for continuity of ground to find the neutral.

Bear in mind that the neutral was allowed to be switched and that wiring it that way was a choice of the installer, it was not a Code issue.

Bear in mind that one threeway wiring method from the K&T era actually changed the polarity of the wires at the lampholder, depending upon the position of the switching. To verify this one, you may find, with the threeway switches removed from the conductors, that there is an unswitched hot and a continuous neutral at each switch box (connected to the threeway travelers) and the switched leg is connected to the threeway common.

Be patient, draw it out, and it will make sense.
 
Having done a lot of work in existing dwellings with Knob and Tube, I'm partial to the Greenlee GT-95 . It has no switches, tests continuity and either contact or non-contact voltage, and does a GFCI test bleed of 6 milliamps. Nothing to forget to prevent a blow up of the tester when going from a continuity test to a live contact voltage test. This tool has greatly reduced the number of times I have to run a "known ground". It comes with two test leads.

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Thanks for all the replies. As crazy as it sounds I keep a 12"x24" dry erase board in my truck just because I ve learned some things for me I need to draw it out.
 
When I used my non contact testor. The single wire the went to lights black was showing hot. But the single wire from white on fixture was not with switch on yet when switch was off white showed hot.
I love figuring out things like this.. Very wide open attic . Single story. Should be easy rewire
 
electricalist said:
When I used my non contact testor. The single wire the went to lights black was showing hot. But the single wire from white on fixture was not with switch on yet when switch was off white showed hot.
I love figuring out things like this.. Very wide open attic . Single story. Should be easy rewire
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Tells me the grounded (neutral) is the conductor that is being switched.

With the switch on or "closed" the white is connected to the grounded conductor and is at ground potential (with only slight elevated voltage because of voltage drop).

With the switch off or "open" the white is not connected to the grounded conductor at all, it does have continuity to the ungrounded conductor through the lamp, but with no complete circuit and no current flow, there is no voltage drop across the lamp so it will read full 120 volts to ground until it gets connected to the grounded conductor again.
 
kwired said:
Tells me the grounded (neutral) is the conductor that is being switched.

With the switch on or "closed" the white is connected to the grounded conductor and is at ground potential (with only slight elevated voltage because of voltage drop).

With the switch off or "open" the white is not connected to the grounded conductor at all, it does have continuity to the ungrounded conductor through the lamp, but with no complete circuit and no current flow, there is no voltage drop across the lamp so it will read full 120 volts to ground until it gets connected to the grounded conductor again.
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It is what you are saying and know I understand how and why. Thank you Sir.
 
electricalist said:
Thanks for all the replies. As crazy as it sounds I keep a 12"x24" dry erase board in my truck just because I ve learned some things for me I need to draw it out.
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i have one in my office for the same reason. if it is not big enough I go to a conference room and use a larger one and take cell phone picture when I am done.

I even have one in my kitchen to use as a grocery list.
 
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