Here are some must-know practical tips about fuses

What is a fuse ? It's a cool little device that self-destructs when there's a power surge or other overcurrent condition. Why would anyone create such a device? Well, the reason is simple: to protect the rest of the circuit the fuse is in. Replacing a fuse is a fraction of the cost of replacing the entire circuit, which could be destroyed.

Since fuses are such a common component that needs to be replaced, we thought it would be helpful to go a little deeper into their purpose, how to test and diagnose them, and show the various fuse types and their different shapes and sizes.

Common sense 1 : How to determine whether a fuse is blown?

If the fuse can be removed from the circuit, the easiest way to determine if it has blown is to do a continuity test. Grab a multimeter and select the continuity or resistance setting. Next do a quick test on the multimeter to determine if it is working properly by touching the leads together until you hear a beep or see a 0 ohm reading.

Now, after verifying that the circuit is de-energized, place the leads on both sides of the fuse, if you hear the same beeping sound, and the multimeter reads a very low resistance, then the fuse is not blown. If you do not hear the beeping sound, and / or the multimeter reads OL , then the fuse is blown.

Another way to test a fuse is to use a digital multimeter to measure the voltage across the fuse. This method is useful if the fuse is not easily removed from the circuit. To do this, first power up the circuit and then switch the multimeter to voltage measurement mode. Make sure DC is selected for a direct current circuit and AC is selected for an alternating current circuit .

Take the appropriate precautions to keep yourself away from dangerous voltages. Place the multimeter leads on both sides of the fuse. If little or no voltage is indicated, the fuse is intact. However, if there is a voltage difference (usually the full supply voltage), the fuse is blown.

Common sense 2 : How to replace the fuse correctly?

The best practice is to replace a bad fuse with a fuse of the same specification. One thing to note is whether the fuse type is fast-blow or slow-blow. In most cases, a slow-blow fuse can be replaced with a fast-blow or slow-blow fuse, but never the other way around. Slow-blow fuses are used in inductive circuits. An example is motor starting. Although the motor is rated for a low current, it draws very high current when starting. When using a slow-blow fuse, the higher current can be allowed for a short period of time, but not for a long time. In this case, if a fast-blow fuse is used, it will blow as soon as the rated current is exceeded. It is best to continue using a device with the same specifications as the original device.

Still have questions or need help with fuses? Watch the video below and check out our Tech Forums post about fuses .