Testing a fuse with an ohmmeter – What resistance reading indicates a good fuse in a high-current system?

Introduction / Context:Fuses protect circuits by opening when current exceeds a rated value. A quick continuity or resistance test confirms the fuse's condition. Understanding expected readings helps avoid unnecessary replacements and downtime.

Given Data / Assumptions:

• The fuse is removed from the circuit (best practice) or the circuit is unpowered.
• Ohmmeter/DMM is functioning and leads are zeroed if needed.
• Fuse is rated for high current (very low internal resistance when intact).

Concept / Approach:

A good fuse behaves like a short conductor and should measure very close to 0 Ω. Small readings such as 0.1–0.2 Ω can be due to lead resistance or contact resistance. Any reading in the multi-ohm range indicates excessive resistance or an open fuse.

Step-by-Step Solution:

Verification / Alternative check:

Continuity mode with audible beep can confirm low resistance. Visual inspection may reveal a broken element, but ohmic testing is more reliable for time-delay types.

Why Other Options Are Wrong:

0.2 Ω can be acceptable in some meters, but the best expected answer is essentially 0 Ω. Readings like 2 Ω or 5 Ω are far too high for a healthy, high-current fuse.

Common Pitfalls:

Testing in-circuit and reading parallel paths; not subtracting lead resistance; poor probe contact causing artificially high readings.

Final Answer:

0.0 Ω (essentially short, near zero).