What measurement methods are valid for testing fuses?

The validity of using resistance measurement and voltage measurement for testing fuses is rooted in the fundamental principles of how fuses operate and the characteristics that indicate their functionality.

Resistance measurement is effective because a properly functioning fuse will exhibit a very low resistance when tested, typically near zero. This indicates that there is a complete circuit and that the fuse element is intact. If a fuse is blown, the resistance would be infinite, signaling that the circuit is open and the fuse must be replaced.

Voltage measurement is also essential for assessing fuses, particularly under load conditions. By measuring the voltage across a fuse while the circuit is energized, you can determine if it is allowing current to pass through effectively. A significant voltage drop across the fuse indicates a potential failure or that the fuse is blown.

These two methods provide a comprehensive approach to fuse testing, ensuring that both the operational status (through voltage measurement) and the integrity (through resistance measurement) can be verified. This combined method aligns with the safety practices outlined in NFPA 70E, which emphasize comprehensive testing to ensure electrical safety in the workplace.