Knob and Tube three way switching

[Mr 3phase]

I have seen a lot, but never this...I was at a house on Friday and the customer told me that one of the stair way lights (there are two) on a three way switch was not working. The light fixture at the top of the stairs had been removed. I looked at the light switch and this is where the 'mystery' begins. The 'switches' are push buttons, two of them on one yoke, both of them are three way in design. One is locate at the bottom of the stairs, the other at the top. The one at the top of the stairs has a single wire going from the 'point' on the three way on the 'top' of the yoke, to the light fixture that is removed. Just a single wire. The other two wires go some where (did not get too deep into it as I was short on time). The 'bottom' three way (bottom of yoke ), has a knob and tube three wire attached to the three screws. The switch at the bottom of the steps works the light at the bottom of the stairs but not the top. The switch at the top of the stairs works the light at the bottom of the stairs but not the top. I have to go back there on Monday. What the heck is this and how does it work?

 

[tryinghard]

Just install new correct cable, don't try to figure it out it may have never been correct.

 

[Dennis Alwon]

Assuming this worked properly at one time I would guess that you lost a neutral or switch leg at one light. Remember k&T will pick up neutrals anywhere on the circuit for the lights. It is possible someone cut the neutral thinking they were cleaning up so K&T wiring.

I would guess that one 3 way has a switch leg to the light that works and somewhere in the wall is a splice to the second light. I also suspect the other 2 are travelers to the other switch. Thus fed at one 3 way and switch leg from the other.

Good luck finding it. Are you sure both lights worked together???

 

[kwired]

Do you have hot and neutral at the switch(es) or just hot and travelers at the first, and travelers and load at the second switch?

running hot and neutral to both switches and then connecting the common terminal of each switch to the lamp was a fairly common practice. If it were not for the fact that it reverses polarity in the lampholder it would still be allowed to do it that way today. (I guess you could still do it for something that is not required to have a certain polarity)

 

[tryinghard]

These old places usually did all their make up in the ceiling or wall light outlets rather than switches. If this is the case the hot is comming from the light as well as the switchleg - but they could be comming from differant lights. The two travelers really should be running uniterupted between the 3-ways.

 

[kwired]

These old places usually did all their make up in the ceiling or wall light outlets rather than switches. If this is the case the hot is comming from the light as well as the switchleg - but they could be comming from differant lights. The two travelers really should be running uniterupted between the 3-ways.

In knob and tube wiring make up was done wherever it was convenient and not in switches or outlets.

What some call "California" or "Chicago" three ways is basically what I described in my previous post and that was common in knob and tube wiring - especially when done across separate floors, It generally used less conductor to do it that way is probably the main reason for it.

 

[Dennis Alwon]

In knob and tube wiring make up was done wherever it was convenient and not in switches or outlets.

What some call "California" or "Chicago" three ways is basically what I described in my previous post and that was common in knob and tube wiring - especially when done across separate floors, It generally used less conductor to do it that way is probably the main reason for it.

I have never seen the neutral and hot used in a 3 way with k&T. I have seen switched neutrals but not both as described in what you call the calif. 3 way. It could also be a travelling bus 2 wire system.

 

[tryinghard]

Again don't assume it's ever been correct, I would just replace with new and most often this is actually a savings to the customer. If your adamant to trouble shoot then test the two 3-way switches first then locate the switch leg, locate the hot, locate the travelers and make em right.

 

[Dennis Alwon]

Replacing 3 way switching on 2 different floor levels is not that easy or desirable.

 

[al hildenbrand]

The one at the top of the stairs has a single wire going from the 'point' on the three way on the 'top' of the yoke, to the light fixture that is removed. Just a single wire.

This sounds like what some have called "a Carter threeway" which is distinguished by the polarity reversing in the lampholder of the fixtures, depending upon the position of the switches.

At each of the two threeway switch locations, a hot and neutral are connected to the switch traveler terminals. The threeway common terminal has the conductor that goes to the light fixture.

In your case, since the homeowner reports that both the light fixtures worked in unison and were controlled by the pair of threeways, the one wire that goes to the second floor light is probably spliced somewhere inside the walls and is continuous between two light fixtures. This one wire will end at the first floor light.

I suspect you will find that the wire connected to the first floor threeway switch common terminal will go up to the first floor light, and continue on to the second floor light, ending there.

This was a legal threeway in it's day, which was early in the 1900s. Once Code changes required the screw shell to always be connected to the grounded conductor this type of hookup was no longer done. Unless there is local ordinance to the contrary, this type of hookup is usually grandfathered.

I agree with Dennis that rewiring this with modern materials is generally not desirable. Because of the framing in and around the stairwell, the labor of installation and repair can be large.

 

[tryinghard]

Upgrading with current wiring as always is situational - of course

 

[kwired]

The first step to troubleshooting this is to figure out what three way setup was used on the original install. So far this thread has mentioned two of what we call unconventional setups today but were common at the time K&T wiring was being installed. Plus there is what we would call normal today with hot hitting one common travelers between switches and the other common hitting the load.

Take some readings to find what conductors you have at switches and at light(s). Removal of lamp so there is no connection between L1 and L2 will make this easier to figure out. Another lead to a known hot or known ground can also be helpful.

I don't recall ever seeing failed K & T, outside of physical damage somehow. Usually someone has replaced or added something and did it wrong, or a device fails.

 

[LarryFine]

Time to break out the wiggy and extension cord, and figure out which wires are what with all switches and loads disconnected.