How to troubleshoot a fuse

Testing of a fuse is one of the easiest diagnosis. It can be done by doing continuity test, by using a test lamp or by checking the voltage at both terminals of the fuse.

Troubleshooting a fuse is one of the easiest things that can be done on electrical and electronic systems.

There are different ways to test a fuse and the suitability of each method depends on the type of circuit that the fuse is used in.

 

What is a fuse?

It is an electrical safety device with thin conductor which is designed to melt and separate for the purpose of breaking the circuit for protection in the case of an excessive current flow through the fuse.

 

Different ways to test a fuse

Below are the different ways a fuse can be tested. They are all easy to understand and carry out.

1. Use of multimeter/continuity tester for fuse test

This entails the use of a multimeter set to continuity range. Fuses are not supposed to be resistive therefore, a good fuse will show no resistance during continuity test. Continuity test is simply a test for current flow (without resistance) from one end of a fuse to the other end of the same fuse. All that you need to do is to put one lead of the tester on one terminal of the fuse and the other lead of the tester on the second terminal of the fuse. Some testers have a buzzer sound that signifies that there is continuity. A good fuse will show zero resistance or a negligible resistance value.

2. Use of test light for fuse test

A test light is just a light bulb that illuminates if there is current in a circuit. One terminal of the test light is grounded (for DC voltage) or connected to neutral (for AC voltage). The other terminal of the test light is then used on the fuse itself. If the bulb lights up when each terminal of the fuse it touched, the fuse is working but if it lights up when one terminal is touched and does not light up when the other terminal of the fuse is touched, the fuse is definitely bad.

3. Determining a bad fuse through physical inspection

Many fuses (not all) have transparent casing that makes it possible to see the thin film of conductor that acts as the fuse. When the fuse is pulled out from the circuit, it can be inspected to see whether the thin film has blown or not. To see the thin conductor of some fuses, the case will need to be opened by loosening screws. Some fuses cannot be tested by using this method because one can neither see the thin film because the casing is opaque nor be able to open the casing as it is a completely sealed unit.

Caution!

All electrical safety precautions must be followed when working on circuits that have fuses to avoid electrical shock and/or damage to the circuit.