household 3-way switch wiring question for electrician?

[semlin]

is there a proper wiring sequence for two 3-way switches going to a light so that all 6 terminals will be cold on a circuit tester when the light is on?

that seems to be the case with my kitchen light. since there is mixed old and new wiring and switches, and the new switch with new wiring just randomly failed with a short in one position I want to be sure it is wired properly.

when light is off, the old switch has a hot common and one of the two switch (traveller?) lines is hot and the other cold. the new switch will have one of the two travellers hot and the common and other traveller cold.

when the light is on, every terminal on both switches tests cold.

it is a 1927 house i bought last year. the old switch and wire is original, the new switch, wire and box looks nearly brand new when we got it.

a little while ago the old switch started working intermittently and today the lights suddenly flickered then died and the lights would not work with either switch in any position.

i tried replacing the old switch with a brand new switch and the light did not work but in one position the new switch i had not replaced crackled. so I replaced that new switch with the brand new switch and reinstalled the old one and everything now apparently works fine. I just want to make sure the whole thing is not wired wrong.

 

[semlin]

additional information. the common connector for the old switch is the incoming "hot" for the circuit.

 

[EdsCruisin]

You need to test again - you can't have all cold wires in a closed circuit.
For the three wires on each switch you should have the following:
Switch A:
One hot wire from the fuse box
Two wires connected to the other switch
Switch B:
Two wires connected to the other switch
One wire connected to the light.

Therefore there are always two hot wires on each switch.

 

[semlin]

it did not seem right to me either, hence I am posting.

i have tested this several times. even the incoming hot power line to the old switch does not light up when the kitchen light is on. i have a screwdriver ac circuit tester that you put your thumb on the end to light up. it is rated 80-250 volts. If the kitchen light is turned off and I put the screw driver on the incoming hot, it lights up. when i switch the kitchen light on, the light goes out.

 

[EdsCruisin]

You must still be tesing the wrong wire. Only one wire is consistently hot regardless of switches. The best way to find it may be to disconnect the switches. Keep in mind that the other two wires on the switch alternate hot and cold when you flick either switch. Take the circuit apart and test incrementally from there.

 

[semlin]

You must still be tesing the wrong wire. Only one wire is consistently hot regardless of switches. The best way to find it may be to disconnect the switches. Keep in mind that the other two wires on the switch alternate hot and cold when you flick either switch. Take the circuit apart and test incrementally from there.

i have done this.

the wire leading to the common on the old switch is hot when i disconnect it from the switch. it is the only one on either switch.

when i reconnect it to the switch it is hot, and at that point one of the travellers on that switch becomes hot and one of the travellers on the other switch becomes hot.

so far, so good.

only, when i turn the kitchen light on suddenly nothing is hot including the incoming hot.

i have wondered if there is a short that is somehow letting the kitchen overhead light work but not my tester. i also wonder if it is the tester seeing a voltage that is not enough for the light to come on or too much ?

 

[Bogo]

*--~s < source
|
|
* <test point
[] 3 way switches and their wiring
* <test point
|
light
|
*--~n < neutral/return

Testing across the input legs to the 3 way switches will light your tester when they are all off and not light it when any is turned on. The potential across the switch changes when the switch is turned on.

 

[Bogo]

i have wondered if there is a short that is somehow letting the kitchen overhead light work but not my tester. i also wonder if it is the tester seeing a voltage that is not enough for the light to come on or too much ?

Yep there is a short, it is right there in the switch. Think about it. The switch is NOT WHERE THE ENERGY IS USED, the light is. There will only be a very tiny voltage drop across the switches (contact resistance) when on, and a large one across the light.

 

[semlin]

so i am good then?

 

[EdsCruisin]

so i am good then?

Not exactly. Instead of testing across the switch, create your own closed circuit by grounding your test lamp. When you ground one side of the lamp, and use the probe end to test each wire, you will see where the power is.

Testing across the switch only tells you what is connected when the switch is in one position or the other, much like a benchtop continuity test. Good, important information, but not solving your dilemma.

 

[semlin]

Not exactly. Instead of testing across the switch, create your own closed circuit by grounding your test lamp. When you ground one side of the lamp, and use the probe end to test each wire, you will see where the power is.

Testing across the switch only tells you what is connected when the switch is in one position or the other, much like a benchtop continuity test. Good, important information, but not solving your dilemma.

i am grounding the test lamp -- finger ground

 

[Pin_Head]

when the light is on, every terminal on both switches tests cold.

If the light is burning brightly, this is normal. You are just measuring a voltage drop across a resistor (the lamp bulb). Put a real AC volt meter on it and you will see that there is power on 4 of the terminals. (or just use your finger).

If the bulb is lit dimmly, then you may have a bad or loose connection upstream of the switch.