A blown fuse can be annoying, but it actually helps prevent electrical damage and fire. Fortunately, fuses are inexpensive and easy to replace. If you don't have power at home or in your car, you can check the fuses just by looking. You should inspect the inside of the fuse in question for black charred marks or a broken filament wire. If you can't detect any obvious signs, you can always use a test light or multimeter to determine if the fuse is working properly.
Steps
Method 1 of 3: Check the House Fuse Box
Step 1. Find the fuse box in your basement or garage
You should look for a metal box with a door, inside which you will find many glass fuses that screw into sockets. Fuse boxes are typically found in basements, garages, laundry rooms, and attics.
- If you are having trouble finding the fuse box, you can check the utility meter outside the home. Try to follow the wire coming out of the meter. Fuse boxes and circuit breakers are typically located close to where power enters the home.
- Older houses have glass fuses that look like light bulbs. You should replace the fuses if they blow. On the other hand, more modern homes have circuit breakers, which only need to be flipped over and reset.
Step 2. Turn off electricity and appliances at the blown circuit breaker
You should find a large switch at the top of the panel and toggle it between "on" and "off." In addition to disconnecting the main supply, you should unplug the appliances you turned off when the fuse blew. This way, they will not overload the replacement fuse when connecting the main supply.
If there is no main power switch, you should detect a large block at the top of the panel. Remove it and check the "on" and "off" labels. If you detect a label, you should re-insert it with the “off” side pointing up. If there is no tag, you should set the block aside while you replace the blown fuse
Step 3. Check the fuses for charred glass or broken filaments
Check for a diagram or labels on the inside of the panel door. If you're lucky, you can also search the room where the power was turned off and locate the corresponding fuse. Twist that fuse counterclockwise, pull it out of the socket, and look for black marks or a broken filament wire on the inside of the glass.
If the fuse box isn't labeled, you should check each fuse individually for charred marks or broken filaments. Once you've found the one that burned, you need to tag it. By labeling the fuses each time you replace one, you will eventually get a complete diagram of the box
Step 4. Replace the blown fuse with one with the same rating
Look for a number on the fuse, indicating its amperage rating. Write down the number or take the blown fuse to the hardware store to make sure you get an identical replacement. Next, plug in the replacement fuse and turn it clockwise to lock it in place.
The fuse rating may vary by country, but common amperages include 15, 20, and 30
Security warning:
Never use a fuse with a higher amperage than the one that blew. Installing the wrong fuse can cause electrical damage or fire.
Step 5. Reconnect the power to test the new fuse
Once you've plugged in the fuse, you should double-check to make sure you disconnect all electrical devices from the faulty circuit. When you're ready, flip the main fuse switch or reinsert the main block to restore power to the house. Then, check the lights or connect electronic devices to test the circuit.
- If the electronics are still not working after replacing the fuse, you should disconnect the main supply and make sure the fuse is properly connected.
- If the fuse blows again shortly after replacing it, you are probably using more electrical devices than the circuit can handle. Try to use fewer devices or unplug nonessential ones when they are out of use.
- If you are still unable to detect the problem, you should call an experienced electrician, as it could mean that the house wiring is faulty.
Method 2 of 3: Troubleshoot car fuses
Step 1. Find the vehicle's fuse box under the hood or dashboard
Many cars have 2 or more fuse boxes, but there is no universal standard for their location. Most manufacturers place them near the car's engine or battery, under the steering wheel, or inside the glove compartment. You should look for a gray or black box that is labeled "fuses."
Consult your car manual if you have trouble finding the fuse boxes. If you don't have a manual, you should look up "fuse box location" plus the year, make, and model of the car online
Step 2. Find the fuse that controls the device that stopped working
Lift the latch on the side of the fuse box to loosen the cover. Look inside the cover for a diagram of the devices that each fuse controls. The manual can also include a diagram, but if nothing else works, you can also look up information about a specific vehicle on the internet.
- The diagram also includes the fuse amperage, which you need to know to buy a replacement.
- Make sure to turn off the car before troubleshooting the fuse box.
Step 3. Use tweezers or extractors to remove the blown fuse from the box
Some car and fuse replacement kits include small plastic pullers, which you can use to pull the fuse out of the box. If you don't have fuse pullers on hand, you can use a pair of pliers. If you have no choice, you can also use your fingers to carefully pry the fuse out of the box.
Make sure the car is completely off before removing the blown fuse. Keep the keys out of the ignition to avoid accidentally putting it into “start” or “accessory” mode. Otherwise, you could receive a nasty electric shock
Step 4. Check the fuse for a broken filament or discolored areas
Car fuses are small, making it a bit more difficult to spot signs that one has blown. Hold it up to the light and look closely for a thin wire connecting both sides of the fuse. If the wire is broken, or you see charred marks, then the fuse has blown.
- If the wire is intact and the fuse appears to be good, you should check the diagram to make sure you have the correct fuse. If you've checked each fuse individually and none have blown, the car's electrical system likely needs a mechanic's attention.
- If you can't visually tell if the fuse has blown, you may need to check the fuses with a multimeter to determine if they are working.
Step 5. Install a new fuse with an amperage that matches the one that blew
Visit an auto store or major retailer's automotive department to get fuses for your car. You should bring the blown fuse with you to make sure you get the right replacement. Once you've purchased the correct replacement, simply insert it into the slot where you removed the blown fuse.
- Make sure the car is turned off before putting the fuse in the empty slot. Press down with a little pressure until it snaps into place.
- Car fuses are color-coded, so if they are a different color, then they don't match. Also, make sure the tooth shape of the new fuse matches the old one. If necessary, you can enlist the help of a store clerk to get the correct part.
Tip:
If the car is disabled due to a blown fuse, you can change the corresponding fuse that controls a non-essential device. For example, if the fuse that controls the ignition has blown, you can temporarily use the one for the radio, as long as both fuses are identical.
Method 3 of 3: Use Devices to Test Fuses
Step 1. Check automotive fuses with a simple test light
Put the key in the ignition and turn it to accessory mode. Open the fuse box and then insert the tester's sensor into the small port on the face of a fuse. If the tester turns on, then the fuse is working properly.
- Using a test light is a great way to detect a blown fuse if you can't identify visual cues (for example, a broken filament or black marks).
- You can find fuse test lights at auto stores, the automotive department of most major retailers, or online. This tester has 1 or 2 tips that fit into the small test ports on the outside of all automotive fuses.
Tip:
You don't need to start the car's engine, but be sure to test its fuses in accessory mode. Otherwise you will not have an electrical current flowing into the fuses. Just remember to turn off the car before removing a fuse.
Step 2. Test a plug-in fuse with a multimeter if you don't see any signs of a blown fuse
Set up your multimeter to test resistance, the setting of which looks like the Greek letter omega, or "Ω." Turn off the main supply switch in the fuse box. Next, remove the fuse you want to test. Place it glass side down on a non-conductive surface (for example, a wooden worktable or laminate counter), so that the end of the metal plug is pointing up.
- Plug-type fuses (commonly found in household fuse boxes) have screw terminals that look like the ends of standard light bulbs. To test it, you need to touch one of the multimeter's sensors to the tip of the fuse terminal. Touch the other sensor on the side of the terminal near where the threaded portion ends.
- If the multimeter shows a resistance between 0 and 5 Ω (ohms), then the fuse is good. A higher resistance means that it is a degraded or potentially blown fuse, and a reading above the limit means that the fuse is permanently blown.
- Like an automotive test light, using a multimeter to test a household plug-type fuse is considered a good solution if you suspect that a fuse has blown, but cannot detect clear visual clues.
Step 3. Use a multimeter to test cylindrical fuses in electronic devices
If the instrument or electronic device is broken, you must remove the fuse according to the manufacturer's instructions. Electronic devices generally use tube-shaped fuses with a glass body and terminals at each end. Set the multimeter to test resistance and place the fuse on a non-conductive surface.
- Touch one of the multimeter's sensors to each of the fuse's terminals. As with plug-in fuses, a resistance reading of 0 to 5 Ω means the fuse is good. A reading higher or above the limit means the fuse is bad.
- You can check cylindrical fuses for broken filaments or charred marks just like automotive and plug-in fuses. However, if you can't see clearly inside the fuse, using a multimeter can help you determine if it works or not.
Advice
- If the replacement fuse blows shortly after installation, the car or house is likely to have a more serious problem. Call a skilled mechanic or electrician for advice.
- Keep some extra fuses on hand in your car or at home so you can quickly repair them when needed.