How To Test a Fuse With a Multimeter?


Several cars and old homes that do not use advanced circuit breakers prevent electrical surge damage with the help of a fuse. These fuses sometimes need to be tested to ensure their functionality and working condition. In case you suspect that your fuse is blown, it is recommended that you test it before replacing it.

Most of the fuses used in homes cannot be inspected with the naked eyes. However, we can test the fuse with the help of a multimeter. This article will tell you everything about fuses, their types, basic working, and how a multimeter can be used to test it in simple and easy ways.

What is a Fuse?

fusefuseFuse, an electrical component, protects equipment and people from the destructive consequences of power surges. It is basically a safety device and offers protection against overcurrent due to overloaded circuits, faults, loose screws, damaged wiring, etc. In case of such an occurrence, the wire within the fuse melts and breaks the circuit, which turns off the power supply to the device.

Types of Fuses

There are multiple types of fuses out there. However, only those with visible terminals can be tested using a multimeter. A few types of such fuses are given below.

1. Plug Type Fuse

Such a fuse is generally used in low-current and low-voltage circuits. The operating range of a plug-type fuse ranges from 0.5A to 30A and up to 150V. Plug-type fuse is most common in circuit protection devices. They are currently being replaced by circuit breakers everywhere.

2. Knife Blade Fuse

Knife blades or NF fuses are mainly used for power distribution applications. They also protect large-sized electrical devices, including drives, motors, etc. You can find them in seven different sizes and the range of 2A to 1600A. The two ends of these fuses, mounted on the fuse base, have knife blades.

3. Automotive Fuse

These fuses are specifically designed to protect the electrical equipment in vehicles. They are rated for electrical circuits that are up to 32V DC. However, a few types of automotive fuses are rated for electrical systems that are 42V as well. They are seldom used in electrical products not used in automotive applications.

4. Cartridge Fuse

These fuses are used for protection against overload in electrical appliances and circuits. They have a cylindrical shape with contact points on both ends. They are generally constructed from glass, ceramic, or porcelain.

Working of a Fuse

A fuse has a wire piece inside it made of an alloy or a metal with a specific melting point. A few commonly used materials inside a fuse include copper, aluminum, iron, lead, etc. When the current flowing through the electrical circuit is larger than the specified value, the fuse wire’s temperature increases. This will eventually melt the fuse wire and lead to the circuit breaking.

The traditional fuse works on the power dissipation principle, which is equated as follows.

P = I²R

When there is an increase in the current flowing through the fuse, there is an increase in power dissipation, which causes the wire inside the fuse to heat up. As the temperature of the wire increases, so does the resistance, which further increases power dissipation. This goes on until the melting point temperature of the wire is reached. The fuse wire melts, and the fuse blows.

What is a Multimeter?

multimetermultimeterMultimeter is a type of tool using which electrical values like voltage, resistance, and current are measured. Basically, the functionalities of a voltmeter, ohmmeter, and ammeter are combined into one single electrical equipment called the multimeter.

How To Test a Fuse With a Multimeter?

Here are the steps to test a fuse with a multimeter.

  • You need first to get a multimeter that can check Ohms. With such a multimeter you can tell whether a fuse is blown or not.
  • Change the settings for Ohm on the multimeter to 20K to measure the electrical resistance.
  • Plug in the testing probes to measure the Ohms.
  • Lightly touch the testing leads to each other to start the test. If the multimeter reading shows ‘0’, it means there is no electrical resistance. When you take the tips away from each other, the reading should be ‘1’, implying maximum resistance.
  • The surface used should be non-metal for accurate testing.
  • Now take out the fuse from your vehicle to avoid electrical overload.
  • Check the fuse visually if it is blown or not.
  • Use the testing leads to check the fuse. When the testing probes touch both fuse ends, the multimeter reading should be close to ‘0’. If the reading shows ‘1’, the fuse has blown and needs to be replaced.

Common Fuses That Needed Testing

A few common fuses that need testing occasionally to avoid any safety risks are listed below.

  • Glass fuse
  • Car fuse
  • Fuses in old houses
  • Thermal fuse
  • Home circuit breaker

How Can You Test Fuses Without Physically Taking Them Out?

You can test the fuses without physically taking them out by using a test light in the following way.

  • Locate the fuse box cover and remove it.
  • Clip the test light’s end to the ‘-’ terminal on the battery and touch the tip to the ‘+’ terminal on the battery. Now touch the test light’s end to the terminal and check whether the light appears. This way, you can check whether the test light is functioning properly
  • Now touch the ends of the test light to both the fuse terminals.
  • If the light is coming on, the fuse is working just fine. If not, the fuse has blown and needs replacement.

Fuse With a Multimeter – FAQs

1. Can a fuse give a false reading on a multimeter?

Ans: Multimeters are generally reliable. However, in rare cases, the multimeter may show a false reading when the fuse is partially blown. In such cases, replacing the fuse to inspect its working is always best.

2. Can a multimeter test all types of fuses?

Ans: As long as you can make contact between the probes of the multimeter and fuse ends, Multimeters can test various fuses, including blade fuses, glass tube fuses, ceramic fuses, and others.

3. Is it safe to test a high-current fuse with a multimeter?

Ans: Yes, it is absolutely safe to test a high-current fuse with a multimeter. However, you need to ensure that the amperage rating of the multimeter is more than the fuse you are testing to avoid any damage to the multimeter.

4. Is it necessary to disconnect power before testing a fuse with a multimeter?

Ans: Yes, you need to disconnect power before testing a fuse with a multimeter to avoid electrical damage and shocks to the multimeter.

5. Can a blown fuse cause sparks or smoke?

Ans: In several cases, a blown fuse will result in smoke and sparks. This happens due to a short circuit or electrical overload. If you notice any sparks or smoke from a blown fuse, immediately disconnect the device from the power source and inspect the situation.

Conclusion

Fuses are crucial safety devices that need to be present in an electrical system. They are mainly used to keep the electrical wires from overheating due to electrical overload or short circuits. This is why it is important to ensure that the fuse in your electrical system is not blown and is working just fine. This article will help you in testing fuses with the help of a multimeter.



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