What is the maximum rating for fuses and inverse time circuit breakers?

• A. 1000 amps
• B. 1200 amps
• C. 1600 amps
• D. 6000 amps

Answer: (D)

The main idea is the size limit for the overcurrent protective device that serves the service conductors or the main feeder. For large installations, fuses and inverse-time circuit breakers are manufactured and permitted up to a 6,000-ampere rating, which matches the needs of big service equipment and feeders. This upper limit ensures the protective device can interrupt the expected fault currents without being undersized, while still protecting the conductors and gear. Smaller ratings, like 1,000–1,600 A, are common for typical residential or smaller commercial setups, but the maximum available and permitted rating for such devices in service equipment is 6,000 A.