Cars and older homes that did not use modern circuit breakers are usually equipped with fuses to prevent damage during electrical surges. Sometimes these fuses need to be tested to make sure they are still in good working order. Testing fuses can be done using a multimeter, which is both quick and easy to learn.
Method 1 of 2: Learning about fuses and multimeters
Step 1. Understand fuses
Fuses are really just wires that aren't built to last, but their purpose is to prevent damage to valuable electrical equipment or prevent fires (especially in homes) caused by power surges. If too much current flows through the fuse, it will literally burn and break the circuit. There are several types of fuses, but the differences are mainly in the appearance. Here's a description of the two most common:
- The fuse is a cylindrical fuse that was previously often and for a long time used for a wide variety of appliances, from homes to small electronic devices. They have metal contact points at both ends and consist of a tube with a wire.
- The flat blade fuse is a common type of fuse used in the automotive industry and especially during the last 20-30 years. They vaguely resemble the plug of a power cord, with two metal pins emerging from a plastic housing that contains the wire. In the past, most vehicles were also equipped with small glass fuses. The blade fuse is easy to insert into the battery, and requires relatively little space to plug in a large number of them together.
Step 2. Learn how a multimeter works
Multimeters measure AC and DC voltage, electrical resistance, and electrical current. To test a fuse, you can use it as an ohmmeter (a meter that tests resistance) or an ammeter (a meter that tests electrical current).
A multimeter has a positive and negative power line. When testing resistance or current in a circuit, the meter will send a small amount of electricity from its own battery which is then passed through the circuit or object
Step 3. Understand why you should test fuses
Testing fuses is the easiest way to find out what's going on in your car or home's electrical systems. That is why it is very important that you master this skill.
- It is easier to test fuses than other electrical equipment. Other car or house components have complex wiring systems of a certain length. Moreover, most car parts can only be tested in car workshops, and this quickly entails costs. Testing fuses with a multimeter is relatively simple and the equipment required is inexpensive and easy to operate.
- Many fuse types provide visual confirmation of the fuse's functionality. They are transparent, so you can see if the wire is still intact. If the translucent part is blackened, it's usually because the fuse has blown. However, some fuses will show a black spot after just a slight overheating, and it could even be the result of an undetected incident from weeks or months ago. If a device doesn't work, you should test the fuses first. If the fuses all still work, there is likely a more serious problem and it may be necessary to call a professional.
Method 2 of 2: Testing a fuse
Step 1. First turn off the device and unplug it
Step 2. Remove the fuse from the vehicle or device
Make sure it is turned off before removing the fuse.
Step 3. Activate and set up the meter
- You can turn the switch to Ω, or OHMS. This will measure the resistance. Before testing the fuse, put the positive and negative wires together and read the info. The number shown should be close to the number you see when you test the fuses.
- Alternatively, you can test the electrical current by placing the meter over the symbol, which looks like an arrow moving along a line.
Step 4. Place a wire at each end of the fuse and then check the display
Since the fuse is little more than a wire - and has no complex parts - it doesn't matter which side receives the positive or negative wire
Step 5. Test the fuse
- When using the multimeter to measure Ohms, what reads should match (or nearly match) the result you get when the two wires touch. If the fuse is blown, you will not be able to read anything at all, or the meter will read O. L., depending on the make and type of meter you are using.
- When using a digital multimeter set up to measure continuity, the meter should beep continuously when you hold the wires near the end of the fuse. That means the circuit is complete. If this doesn't happen, the fuse is blown.
- As for the car fuses, most cars use colored flat plug fuses, and if you look at the top of the fuse in the fuse box you will see that there is a metal strip running along the visible top of the fuse and it is either intact (fuse good) or broken (fuse blown).
- Household installations must not only be protected by ordinary fuses these days. The modern circuit breakers and the protective devices do not require fuses and are also much safer. Consider replacing an old fuse installation with one that meets modern standards.
- Never test a fuse on a machine that is still energized.
- Never replace a blown or suspect fuse with a higher rating. They are designed for the safety aspects and you should always replace them with a fuse with exactly (or sometimes lower) rating as the old one.