Which piece of distribution equipment is primarily used to switch circuits on and off?

The piece of distribution equipment primarily used to switch circuits on and off is the circuit breaker. Circuit breakers are designed to interrupt the flow of electricity in a circuit when a fault condition, such as an overload or short circuit, occurs. This action not only helps to protect the electrical system from possible damage but also allows for the safe and convenient operation of switching circuits on and off as needed for maintenance or power management.

In contrast, transformers are used to change the voltage levels in an electrical system but do not function as switches. Feeders are conductors that deliver electrical power from one location to another but also do not serve the role of switching electricity. Distribution panels, while they house multiple circuit breakers, provide the mechanism for circuit distribution and protection rather than directly functioning as a switch themselves. Hence, circuit breakers uniquely fulfill the specific role of switching circuits on and off within the electrical distribution system.