This requires a cable and a circuit.

They require a protective circuit to limit peak voltage.

This requires an electrical circuit with an 'igniter' and a Electrical ballast.

Mercury arc valves require an external circuit to force the current to zero and thus turn off the valve.

Magnetic fields require a continuous circuit, thus more than one pole.

This operation requires a suitable circuit, which has to:

With the old two-wire loop technology, this would require an engineered circuit with increased costs.

The current also requires an external circuit to generate, using a system known as a charge pump.

Larger units may require 230-volt service and a dedicated circuit.

The "strike" requires an electrical circuit with an igniter and a ballast.