of electrical shock when changing the bulb. This method is therefore prohibited in modern building wiring.
More than two locations
For more than two locations, two of the interconnecting wires must be passed through an intermediate switch, wired to swap or transpose the pair. Any number of intermediate switches can be inserted, allowing for any number of locations. This requires two wires along the sequence of switches.
Using three switches, there are eight possible combinations of switch positions: four with the light on and four with the light off. Note that these diagrams also use the American electrical wiring names.
As mentioned above, the above circuit can be extended by using multiple 4-way switches between the 3-way switches to extend switching ability to any number of locations.
Switches built to North American standards identify the terminals by color-coding. The common is often colored black and the pair of traveler connections often colored gold. There is no standard for indicating the terminals on 4-way switches, so they may need to be checked with a meter or a continuity tester to deduce the internal contacts.
Most electricians know these simple guidelines when wiring multiway switching.
- The lightbox always needs a neutral.
- Either one switchbox or the lightbox has hot and neutral from the mains.
- The common terminal of one 3-way switch goes to a hot from the mains, and the common terminal from the other 3-way switch goes to the light.
- The traveler terminals connect to each other at each switchbox.
- Usually a 3-conductor cable is connected between the multiway switches. A pair of conductors for travelers, and the remaining conductor for either neutral or hot conductor. This is dependent on which box the mains are in.
- Only a 2-conductor cable is needed between the light and one of the switches if the switches are connected directly.
- 3-conductor cables are needed between the light and each switch if the switches are not connected directly via another path.
Low voltage relay switching
Systems based on relays with low-voltage control circuits permit switching the power to lighting loads from an arbitrary number of locations. For each load, a latching relay is used that mechanically maintains its on- or off-state, even if power to the building is interrupted. Mains power is wired through the relay to the load.
Instead of running mains voltage to the switches, a low voltage—typically 24 V AC—is connected to remote momentary toggle or rocker switches. The momentary switches usually have SPDT contacts in an (ON)-OFF-(ON) configuration. Pushing the switch actuator in one direction causes the relay contacts to close; pushing it in the opposite direction causes the relay contacts to open. Any number of additional rocker switches can be wired in parallel, as needed in multiple locations. An optional master control can be added that turns all lights in the facility on or off simultaneously under the control of a timer or computer.
After an initial burst of popularity in the 1960s, residential use of such relay-based low voltage systems has become rare. Equipment for new installations is not commonly carried by electrical suppliers, although it is still possible to find parts for maintaining existing installations.
Electronic remote switching
As of 2012, multiway switching in residential and commercial applications is increasingly being implemented with power line signalling and wireless signalling techniques. These include the X10 system, available since the 1970s, and newer hybrid wired/wireless systems, such as Insteon and Z-Wave. This is particularly useful when retrofitting multi-way circuits into existing wiring, often avoiding the need to put holes in walls to run new wires. See home automation for more details.
Remote-control systems are increasingly used in commercial buildings as part of lighting systems under semi-automatic control, for better safety, security, and energy conservation.
- NEC Article 404.2 Switch Connections: (A) ... Three-way and four-way switches shall be wired so that all switchin