How does a fuse differ from a circuit breaker in LV installations?

• A. Fuses are resettable protective devices; circuit breakers are single-use devices.
• B. Fuses interrupt fault currents automatically; circuit breakers require manual operation only.
• C. Fuses interrupt fault currents through thermal heating and are not resettable; circuit breakers are resettable protective devices.
• D. Fuses and circuit breakers operate identically.

Answer: (C)

The key idea is how each protective device handles fault current and what happens after it trips. A fuse uses a metal element that heats up when current exceeds its rating; that heat causes the element to melt and the circuit opens. Because the element is consumed by the fault, a blown fuse can’t be reset—you replace the fuse. Circuit breakers, on the other hand, are resettable protective devices. They sense an overload or short circuit, trip to open the circuit automatically (through thermal and/or magnetic mechanisms), and after the fault is cleared, you can reset them to restore power. This resettable, reclose capability is a fundamental difference from a fuse.

In LV installations, this distinction matters for maintenance and system operation: fuses provide simple, fast protection but require replacement after any trip, while circuit breakers offer convenient re-energizing and the ability to coordinate protection with other devices.

The other descriptions don’t fit because they misstate these basics. Fuses are not resettable, and breakers do not require manual operation only—breakers can trip automatically and then be reset. They also do not operate identically.