Traveler switch wiring

[Open Neutral]

I recall reading of a ?3/4?-way switch wiring scheme that was used in long tunnels.
When you got to the point between say segment 3&4, there was a switch.
Changing it would illuminate the #4 segment and extinguish the #3 lights; the same thing happens
at 4-5, etc.

What's it called and how is accomplished?

 

[retirede]

I would think of it as a set of several independent 3-way circuits. The switches at the intermediate points are essentially two separate 3-way switches with a common handle (DPDT).

There may be more elegant (complicated?) ways to accomplish.

 

[drcampbell]

One method is using an occupancy detector for each segment, with relays to also light up the segment ahead and the segment behind.

 

[Open Neutral]

To be clear, I don't need to implement this, rather I was seeking the solution I'd read about because it was clever.
It might have been a code exception.

 

[wwhitney]

I'm going to assume the lights are halfway between the switches, and power originates at one end of the tunnel (call it the right side).

For the case where when someone exits the tunnel at one end, the next person always enters from that end, then you can do it with 2.5 circuit conductors between switch locations.

Each light gets a leg from the light to the switch located to its left, that's the 0.5 conductors. Each switch is a 3-way switch. One circuit conductor is just the return (grounded conductor if one circuit conductor is grounded) and is connected to one side of each light and none of the switches, as usual. At each switch, the other conductor coming in from the right goes to the common of the 3-way switch; the light and the other conductor going to the left are on the other two terminals.

The initial state is for entering the tunnel from the right; all the switches are set to connect the right hand conductor to the light, rather than send power onwards to the left. The rightmost switch has no light, it's just on-off. You enter the tunnel and flip it on, the light in front of you turns on. Your reach the next switch, toggle it, and the light behind you turns off (no longer supplied from that switch), but the light in front of you turns on (power now reaches it, and it is set to power than light, rather than pass power onward). Etc. (This could use a diagram). The last switch is also just an on-off switch, as there's nowhere to the left to send power onward you.

Some more thought will be required to allow for entry from either end of the tunnel regardless of which end was last exited. I suspect it will require one more conductor the length of the tunnel.

Cheers, Wayne

 

[LarryFine]

I'm thinking of the old apartment-building stairwell lighting that had a switch on each floor that would turn on the next light up or down, depending on your direction.