The controlled load is often a lamp, but multiway switching is used to control other electrical loads, such as an electrical outlet, fans, pumps, heaters or other appliances.
In the Carter system, the incoming live energized and neutral wires were connected to the traveler screws of both 3-way switches, and the lamp was connected between the common screws of the two switches.
Common practice in wiring a multiswitch circuit is to use two-conductor black and white cable from panel to the first switch, and then three-conductor black, red, white cable between pairs of switches.
If you haven't already taken a photo of the original wiring, now's the time.
When the left switch is toggled, it connects to the upper circuit and now the circuit is open at the right switch which turns off the light.
Questions or Comments?
Controlling a light with three or more switches For more than two switches, one or more 4-way switches are added between the 3-way switches.
An intermediate switch can, however, be implemented by adding appropriate external wiring to an ordinary six terminal DPDT switch, or by using a separate DPDT relay.
Switching a neutral is generally forbidden by the NEC unless the hot conductor is opened simultaneously.
Multiple Switch Wiring.
This wiring system may still be encountered in older "grandfathered" electrical installations.