Cars and older homes that do not use modern miniature circuit breakers use fuses to prevent damage to the electrical system. You can test the fuses using a multimeter. A multimeter is a tool that measures electrical current, voltage, and resistance.
Steps
Part 1 of 2: Knowing the Fuses and the Multimeter
Step 1. Learn what fuses are
These are electrical connectors whose purpose is not to last a long time but to prevent damage to the system and expensive devices or to avoid fires (especially in the home) caused by overvoltages. If too much electrical power hits the fuse, it literally "blows" and breaks the circuit. There are many types of fuses, but the differences are almost always in appearance. Here are the descriptions of the two most popular models:
- The cartridge fuse is cylindrical in shape and has been the most used model in many electrical devices for years, from homes to small appliances. This type of fuse has a metal contact or terminal points on the ends and is usually a main tube that contains an electrical wire.
- Blade fuses are the most common on cars manufactured in the last 20-30 years. They vaguely resemble an electrical plug with two metal tips protruding from a plastic housing, which itself contains a metal wire. Previously, cars were equipped with small glass cartridge fuses. Blade fuses fit in rows and take up relatively little space in the box despite being in large quantities.
Step 2. Understand how a multimeter works
This meter measures the voltage of the direct and alternating electric current, the resistance and the flow of current. To test a fuse you must use the multimeter as an ohmmeter (i.e. an instrument that measures resistance) or as an ammeter (the instrument that measures current flow).
A multimeter has a positive and a negative terminal. When you test the resistance or amperage, the meter transmits a small amount of electricity from its batteries and measures what is able to pass through the circuit or object under test
Step 3. Understand why you need to check the fuses
This is the simplest procedure for examining the condition of the electrical system of the car or house and for this reason it is important to know how to move.
- It is easy to check the fuses rather than the whole system or device. Both the house and the car have very complex systems with complicated and long wiring. In addition, most cars can only be fully inspected in workshops, which requires a lot of expense. In comparison, therefore, testing with a multimeter is much simpler and requires easy-to-use and inexpensive tools.
- Many types of fuses allow you to carry out a visual check that they are working properly. They are constructed of clear material, so you can check that the inner thread is still intact. If the transparent area is blackened, usually it means that the fuse has blown. However, some fuses only turn dark because they have overheated slightly due to an imperceptible anomaly that occurred weeks and months earlier. If the device doesn't work, you should check the fuses. If the fuse is in perfect condition then the damage is quite serious and you need to call a technician.
Part 2 of 2: Check the Fuse
Step 1. Turn off the device first and unplug the connections
Make sure the system is turned off before removing the fuse.
Step 2. Turn on and set up the multimeter to measure continuity
Rotate the selector dial so that it points to the symbol indicating continuity, represented by 5 curved vertical lines. Before testing the fuse, connect the positive and negative terminals together and listen for the multimeter's beep to indicate that it is working.
If you want to measure resistance, have the ring point to the Ω or "Ohm" symbol
Step 3. Connect a terminal to each end of the fuse and read the number that appears on the display
Since the fuse is little more than a metal wire, there is no need to worry about polarity and therefore it does not matter which end is connected to the positive or negative terminal.
Step 4. Test the fuse
Listen for the multimeter beep to indicate continuity while holding the probes on the fuse terminals. If the device makes no sound, the fuse is blown and should be replaced.
- If you are using a digital multimeter to check resistance, put the probes against each other to get an initial reading. Then, connect each to one fuse terminal; if the fuse is good, you should get a similar value. If you don't read anything or "OL" is displayed, the fuse is blown.
- If the multimeter reports "Open" or "Not complete", the fuse is broken.
Advice
- Most cars use a different colored 'blade' type fuse; looking at the top of those inserted in the box, it will be possible to see a metal strip that runs along the top of the fuses themselves. This is intact if the fuse is good or broken if the fuse is blown.
- Today's domestic systems should not be protected solely by fuses. Modern miniature circuit breakers and protection devices use less fuses and are much safer. Consider replacing an old fuse system with one of more modern standards.
Warnings
- Never test a fuse on equipment that is still on.
- Never replace blown fuses with those of higher amperage. They are rated for safety measures and should always be replaced with one of the same (sometimes even lower) amperage as the old one.
