Which device is used to energize or de-energize transformers and voltage regulators?

• A. Circuit Breakers
• B. Disconnects
• C. Fuses
• D. Relays

Answer: (A)

Energizing or de-energizing a transformer or voltage regulator is done by a circuit breaker. A breaker can close to supply power to the equipment, or open to remove power, all under control. It also protects the circuit by interrupting fault currents if something goes wrong, which is essential when bringing equipment online or taking it offline safely.

Disconnects mainly serve to isolate equipment for maintenance after it’s de-energized; they aren’t designed to carry or interrupt current during normal operation. Fuses are protective devices that interrupt current if a fault occurs but must be replaced after they blow, so they don’t provide a controllable on/off energize/de-energize function. Relays are sensing/control devices that trigger other equipment actions, not the devices that physically connect or disconnect power themselves.