In which locations must switch legs be used?

Switch legs are essential in electrical wiring to control lights or lighting fixtures from a switch. When a switch is used to turn a fixture on and off, a switch leg connects the switch to the fixture. This allows the flow of electricity to be interrupted by the switch, enabling control over the lighting. When the switch is turned on, electricity flows through the switch leg to the light fixture, illuminating it.

The other options, while related to electrical work, do not correctly define the use of switch legs. Connecting multiple outlets in a circuit involves creating branch circuits without the need for a switch leg, as it deals more with the distribution of power rather than control. Increasing the power of an electrical appliance is generally managed through load management and circuit design, not through the use of a switch leg. Grounding electrical connections is a separate aspect of electrical safety and system design that ensures safety from faults; it does not involve the switch leg concept.