Which of the following is an example of an energy-isolating device?

A circuit breaker is an example of an energy-isolating device because it is specifically designed to interrupt the flow of electrical energy in a circuit. This function is crucial during maintenance or repair work, as it helps prevent accidental energization of equipment, thereby protecting workers from electrical hazards. Energy-isolating devices are essential in ensuring that machinery or electrical systems are completely powered down and cannot be accidentally turned on while personnel are working on them.

In contrast, pushbuttons, selector switches, and control panels do not serve the same purpose. While they control the operation of equipment or can change its settings, they do not isolate energy in the same definitive way. Control devices like pushbuttons and switches typically allow for the flow of energy when engaged, while the control panel manages various operations without necessarily providing the complete isolation required for safety during maintenance activities.