s 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 switching is done only in the ungrounded circuit conductor ... (B) Grounded Conductors. Switches or circuit breakers shall not disconnect the grounded conductor of a circuit. Switching a neutral is generally forbidden by the NEC unless the hot conductor is opened simultaneously
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