It's irritating when a fuse blows, whether in the house or the car, but it actually prevents major electrical damage and even the system from burning down. Furthermore, fuses are cheap and easy to change. Just looking at the fuses should be safe if power is not being supplied; scan the inside of them and check for black marks or a broken filament. If nothing obvious is found, tests can be done with a polarity pen or multimeter to find out if the fuse is working or not.
Steps
Method 1 of 3: Checking a House's Circuit Board
Step 1. Find the distribution circuit board (QDC), a metal box with a door, which should be located in the basement
It is also known as a “fuse box”, as inside there will be several glass fuses screwed into sockets. They are often installed in basements and garages, but homes with more than one floor may have one picture per level.
- You can go to the power meter outside the house so you can find the fuse box if you are having difficulty. Follow the wire coming out of the meter; are switchgear and circuit breakers must be located near the point where power enters the room.
- In older homes, fuses can look like light bulbs, and when they blow, they need to be replaced. In the newer ones, there are circuit breakers, which disable the power during peaks and electricity problems; just pull the lever again to reactivate the power.
Step 2. Turn off the power and disconnect the appliances from the burnt circuit
Look for a large switch at the top of the panel, sliding it from “On” to “Off” position; in addition to turning off the central electricity supply, it is recommended to unplug all appliances that turned off after the fuse problem, so that the new fuse does not overload when turning the power back on.
If there is no main switch or lever, see if there is a large block at the top of the panel. Pull it out and see if there are “On” and “Off” buttons; if so, replace it with the “Off” side facing up. Otherwise, leave this part aside when replacing the fuse
Step 3. Check for burnt glass or broken filaments in the fuses
On the inside of the panel, look for a label or diagram that identifies the exact part where power has dropped so that you know which fuse should be replaced. Turn it counterclockwise to unscrew it, and look at the inside of it, looking for spots with signs of burning or burst filament.
If there is no identification on the switchboard, analyze each fuse individually, looking for signs that the filament has broken or it has blown. Once you find the defective one, identify it with a tag, for example; whenever there is a problem with the fuses, you can gradually create the complete diagram of the box
Step 4. The fuse must be replaced with one of the same amperage
See if there's a number on it and write it down, or take the fuse to a hardware store and have employees help you buy the right one. Then, just snap it into the socket and turn it clockwise to secure it.
Fuse amperage varies by country. In Brazil, the current value is between 10 to 30 amps
security notice: under no circumstances install a fuse with amperage greater than the defective one. There is a risk of damaging the entire electrical system and even causing a fire.
Step 5. Reactivate the electricity to test the newly installed fuse
After connecting, confirm that all electrical devices have been removed from the circuit in question, and when ready, pull the main lever to restore power to the home. Test the circuit by checking lights or connecting electronic devices.
- If they still don't work even after replacement, turn off the power again and confirm that the fuse is securely fastened.
- It is possible that you are using more electronic devices than the circuit supports, especially if the replacement breaks again. Try to use a smaller amount or disconnect non-essential appliances that are not in use.
- It is recommended to call an electrician if the problem persists. It is possible that there is a problem with the electrical wiring in the house.
Method 2 of 3: Troubleshooting Car Fuses
Step 1. Find the car's fuse box under the dashboard or hood
Nowadays, there are many cars with two or even more fuse boxes, but there is no universal standard regarding where they are installed. Usually, automakers put it near the battery or engine, under the steering wheel or even inside the glove compartment. Look for a black or gray compartment and see if there are any inscriptions, such as “Fuses”.
Consult your car manual if you are having difficulty finding the boxes. Those who do not have the document can do an online search: type “location fuse box” and then add the maker, model and year of your vehicle
Step 2. Find the fuse that controls the device that stopped working
Lift the latch on the side of the box so that the lid releases; inside, on it itself, there should be a diagram of the car devices that each fuse controls. The manual may also have the schematic, but if nothing goes well, go to a search engine and enter your car model to see if there is other information about the fuse box.
- In this diagram, the amperage of the fuse should also be written, which is important when changing it.
- Don't forget that the car must be turned off before handling these parts.
Step 3. Remove the blown fuse with tweezers or a tool for removing them
There are kits that can be purchased with this item, which facilitates the output of the installed fuse, but they are not so common in Brazil. A pair of pliers or tweezers will come in handy; in case of emergency, try to take it by hand.
Confirm that the car is turned off, even with the key out of contact, so as not to accidentally turn it and get a dangerous shock
Step 4. Check the fuse for discoloration or a broken filament
As they are small parts, it is a little more complicated to see if there was any problem; try holding them up to the light and see if the filament, which connects the two sides, has become disconnected. This indicates that there has been a break, while burned parts signal that the fuse has blown.
- When you see that the wire is intact and the fuse is not faulty, check the diagram once more to confirm that it is the same one that is defective. You may need to take the car to the mechanic to check the electrical parts for a problem, especially if you don't find blown fuses.
- In this case, you may need to check with a multimeter to see if the fuses are working.
Step 5. Install a new fuse, with the same amperage as the old one
Go to an automotive supply store with the defective part and talk to an employee to tell you which exact product you should buy. Then just insert it in the same place where the previous fuse was.
- Do not forget that the vehicle must be turned off before inserting the fuse. Apply a little pressure until it clicks.
- Automotive fuses are differentiated by color, so you can tell that one of them won't work if the color isn't the same. Also, see if the claw shape of the new part is the same as the previous one; if you are having difficulties, ask an employee at the store for help.
Tip: If the car does not work due to the problem with this fuse, you can change it to another one, as long as it is identical, that controls a non-essential feature of the car, such as the radio.
Method 3 of 3: Using Fuse Test Devices
Step 1. Perform a simple light test to check automotive fuses
Put the key in the ignition and turn it to “ACC”; open the fuse box and place the pen pole into the small slot in front of the fuse. If the pen light turns on, the part is working normally.
- This test is great for finding faulty fuses when no obvious signs are found, such as a broken filament or a burn mark.
- You can buy this equipment on the internet or in automotive supply stores. Some pens have one or two prongs that fit on the outside of all automotive fuses.
Tip:
there is no need to start the car engine, but always test the fuses by turning the key to “ACC”, or they will not be supplied with electrical current. Remember that it is necessary to switch off the car before removing the fuse.
Step 2. Use a multimeter to test fuses with no signs of blown
Set the device to measure resistance (with the Greek letter omega “Ω”) and turn off the box's main power switch. Remove the fuse to be tested and insert it with the glass side facing down on a non-conductive surface, such as a wooden or laminated bench, so that the metal connector is facing up.
- Glass fuses, most common in domestic switchboards, have screw-in terminals, similar to normal light bulbs. Test by touching one of the multimeter's poles at the very tip of the fuse terminal, while the other pole should touch the side of the terminal, near the end of the thread.
- If the resistance measured by the multimeter is from 0 to 5 Ω (ohms), it will be normal. The greater the resistance, the greater the wear (perhaps even signaling that it was burned), while the “OL” reading (“over limit” or over limit) means that it has definitely blown.
- As well as the automotive pen test, the use of the multimeter also works for checking house fuses, especially if no defects are found after observation.
Step 3. Use a multimeter to analyze cylindrical fuses in electronic devices
Instruments and electronic devices that are not working can also be tested; just remove the fuse according to the manufacturer's instructions. Generally, electronic devices have this piece in the form of a tube, with a “body” of glass and terminals at each end. Set up the multimeter to check resistance and place the fuse on a surface that does not conduct electricity.
- Touch one of the multimeter's poles to the two fuse terminals. Again, the reading should be from 0 to 5 Ω; higher values indicate that he has a problem.
- Look for broken filaments or burn marks on cylindrical fuses in homes and automobiles. Still, testing with the multimeter can help you confirm his status, especially if you can't see inside.
Tips
- There may be another fault with the car or with the wiring in the house if the new fuse also blows. Contact an electrician or mechanic for further investigation.
- Always have a few extra fuses stored both in the car and at home so that you can make the repairs quickly, when necessary.
