When testing fuses, which measurement methods are acceptable?

• A. Resistance Measurement or Voltage Measurement
• B. Capacitance Measurement or Inductance Measurement
• C. Temperature Measurement or Friction Test
• D. Sound Level Measurement or Visual Inspection

Answer: (A)

Fuses are protective devices that either conduct normally or open the circuit when blown, so the test must reveal whether they still carry current. Checking continuity with a resistance measurement is direct: with the circuit de-energized and the fuse isolated, a good fuse shows very low resistance (almost a short), while a blown fuse shows very high resistance (open circuit). If you test under power, a voltage measurement across the fuse can also indicate status: a functioning fuse will have almost no voltage drop across it (input and output nearly equal), whereas a blown fuse will show a full supply on the side feeding the fuse and little or no voltage on the load side, indicating no current flow. The other methods—capacitance, inductance, temperature, friction, sound level, or visual inspection—do not reliably indicate whether the fuse is conducting or not and aren’t appropriate for confirming fuse condition.