Which type of protective device provides a time delay and must be replaced when actuated?

Which type of protective device provides a time delay and must be replaced when actuated?

• A. Fuse
• B. Circuit Breaker
• C. Relay
• D. Pressure switch

Answer: (A)

Time-delay protection that is sacrificial is provided by a fuse. A fuse uses a filament or conductor that melts after overheating from excessive current, and there are time-delay (slow-blow) fuses that allow short surges or inrush currents before opening. Once it has operated and opened the circuit, it must be replaced to restore protection. Circuit breakers can trip and be reset, so they are not replaced after acting. Relays are control devices that trigger protection, not the protective device itself. Pressure switches monitor pressure and aren’t the protective current-interrupting device.

Time-delay protection that is sacrificial is provided by a fuse. A fuse uses a filament or conductor that melts after overheating from excessive current, and there are time-delay (slow-blow) fuses that allow short surges or inrush currents before opening. Once it has operated and opened the circuit, it must be replaced to restore protection.

Circuit breakers can trip and be reset, so they are not replaced after acting. Relays are control devices that trigger protection, not the protective device itself. Pressure switches monitor pressure and aren’t the protective current-interrupting device.