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Discussion Starter #1
I'm trying to replace a couple 3 way switches. They're old switches and the wrong color. When I wire the new switch the same as the old the breaker trips. The wiring appears to be 1940s original and doesn't match 3way switch diagrams Ive looked at. I've tried wiring new switch various ways with same result. What's the deal?

Photo and my attempt at a diagram attached. I labeled the wires that are always hot and ones that control the lights

 

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Daniel,
A few things to know about a 3-way circuit. There is no off position. There is a common screw on each switch. There are 2 travelers on each switch. The simplest configuration is power into one switch, travelers to the next switch and a light out of the second switch. And current has no idea of the color wire it is traveling across.


You need to determine what wire is the line coming in. It may be at either device. That wire should not go any further past that one switch. You need to determine what wires are the load. They may be in either box. One screw on each switch will be(should be) black. That screw will be the common. The other two are travelers.



There will be many different configurations depending on where the line comes in to the circuit, and where the load is connected to the circuit. Without knowing those two variables, it will be difficult to tell you how to wire the circuit without being there to take the voltage and ohm readings.


Andrew
Handy Andy In Mt Airy NC
 

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Discussion Starter #3
Thanks for the general explanation. To clarify a few things:

(1) three way switches are already hooked up. I'm just replacing a couple in the downstairs box.

(2) I have two sets of 3way switches.

(3) here's a better diagram. I took a voltage tester and identified the wires that are always hot regardless of switch position and those that vary depending on switch position.

How can I identify the line/load?
 

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Your diagram can not work as drawn in the upper diagram. There is no way there should be any connections between light1 and light2 except the always hot at the bottom which would be the common screw connection.

Same with the upstairs light. There should be NO connections between the two switches.
 

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Upon further review I think what you have there is a carter or California three way.
I have marked on the diagram the common connections in red.

Untitled.png

Please note that with this system there is ALWAYS power at the fixture.
 

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Carter three way. Hot and neutral are attached to the travellers at both ends. When the light is off you have either two hots or two neutrals connected to the light.
When the light is on the hot connection switches between the shell and center point depending on the switch position.

300px-Carter-system.svg.png
 

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retired framer
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Carter three way. Hot and neutral are attached to the travellers at both ends. When the light is off you have either two hots or two neutrals connected to the light.
When the light is on the hot connection switches between the shell and center point depending on the switch position.

View attachment 541341
Does that mean he is just working with 2 wire?
 

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Discussion Starter #10
Progress! Great work. What does this mean for replacing my switches? Electrical system overall? Burning down my house?

Another bit of info, the two wires on the left of the downstairs box are labeled "ground", even though it's clearly not a ground and the common wire is labeled "button". Not everything in my house is wired like this. I think other circuits have been replaced overtime.
 

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retired framer
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Progress! Great work. What does this mean for replacing my switches? Electrical system overall? Burning down my house?

Another bit of info, the two wires on the left of the downstairs box are labeled "ground", even though it's clearly not a ground and the common wire is labeled "button". Not everything in my house is wired like this. I think other circuits have been replaced overtime.
I would take ground to mean neutral. Joe will know the rules of replacing switches.
 

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Discussion Starter #12
Here's a photo inside the box. I haven't encountered anything like this doing other minor electrical work, so guessing most of this stuff has been updated at some point. I have grounded outlets throughout and there's a new circuit box. House was built in 1940.

 

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retired framer
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Here's a photo inside the box. I haven't encountered anything like this doing other minor electrical work, so guessing most of this stuff has been updated at some point. I have grounded outlets throughout and there's a new circuit box. House was built in 1940.
It gets better, is that aluminum and copper on the same brass screw.:surprise:
 

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Discussion Starter #14
More pics. Last 4 of the old switch. It was wired as shown in diagram.

Thanks for the help. I guess I have two questions now: 1) Can a standard modern switch work? Any thoughts on how to wire? 2) considering the mess, should I just call a pro?

Guessing this was left due to the difficulty of replacing three way switches across two floors. Would rather not bare that expense now if replaceable.

 

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Discussion Starter #17
I got it thanks to Joe's insight. Will probably rewire it when I replace the fixtures. I think it's the last of the knob and tube in the house
 

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retired framer
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Those run right over the box and back into the wall. Guess I should figure out what they're doing.

So what are my risks with leaving this? Shock when changing light bulbs?
They may be phone cables, maybe just tape over the screws that are close to them.
 
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