Blown fuses can be a common household problem, but they are easy to fix. A blown fuse can cause a loss of power to a single appliance or to an entire circuit. If you are experiencing a loss of power, the first step is to check the fuses. Fuses are small, cylindrical devices that protect electrical circuits from overloads. When too much current flows through a circuit, the fuse will blow, breaking the circuit and preventing damage to the appliances or wiring. Fuses are typically located in a fuse box or panel, which is usually found in the basement, garage, or utility room.
There are two ways to test a fuse: visually and with a multimeter. To test a fuse visually, look for a break in the wire inside the fuse. If the wire is broken, the fuse is blown and needs to be replaced. To test a fuse with a multimeter, set the multimeter to the ohms setting and touch the probes to the two metal terminals on the fuse. If the multimeter reads infinity, the fuse is blown and needs to be replaced. If the multimeter reads a low resistance, the fuse is good.
Once you have identified the blown fuse, you will need to replace it with a new fuse of the same amperage. Fuses are available in a variety of amperages, so it is important to choose the correct one for your circuit. If you are not sure what amperage fuse to use, consult the owner’s manual for your appliance or the electrical code for your area. Once you have replaced the blown fuse, the power should be restored to your circuit.
Identifying the Fuse Box
Locating the fuse box is the initial step in testing a fuse. Unlike circuit breakers that flip when a circuit overloads, fuses require replacement once blown. To begin, review your vehicle’s owner’s manual for the fuse box’s precise location. It’s commonly found:
Under the Hood: Lift the hood and search near the battery or firewall for a rectangular, black plastic box marked “Fuse Box” or “Fuses.” Locate the primary fuse box, as there may be additional smaller ones elsewhere.
Inside the Vehicle: Check under the dashboard on the driver’s side. Look for a panel or cover that says “Fuses” or has a symbol resembling a lightning bolt. Remove the panel to access the fuse box.
Glove Box: Open the glove box and inspect its back panel. Some vehicles have fuse boxes conveniently located there.
Trunk: Lift the trunk lid and search for a small panel on one side. It may be marked “Fuses” or have a fuse symbol.
Additional Considerations:
- Fuse boxes often contain a diagram or chart identifying the fuse’s purpose (e.g., “Headlights,” “Radio”).
- Vehicles may have multiple fuse boxes, so be sure to check all potential locations.
- In rare cases, a fuse box may be located in an unconventional place. Consult your vehicle’s manual if you encounter difficulties finding it.
Visual Inspection of the Fuse
Before using a multimeter to test a fuse, a visual inspection can often reveal whether the fuse is blown. Here’s how to perform a visual inspection:
1. Check for Physical Damage
Examine the fuse for any physical damage, such as cracks, bulges, or discoloration. These signs may indicate that the fuse has blown or is damaged.
2. Inspect the Fuse Element
Look at the fuse element, which is the thin wire or metal strip that runs through the center of the fuse. If the element is broken or melted, it indicates that the fuse has blown.
3. Check for Discoloration
Examine the fuse body for any discoloration. If the fuse is blown, it may have a blackened or scorched appearance.
Fuse Coloration Guide
| Color | Indication |
|---|---|
| Blackened or scorched | Blown fuse |
| Intact | Good fuse |
Using a Multimeter to Test Continuity
To test a fuse using a multimeter, set the multimeter to the ohms (Ω) setting. This setting measures resistance. A working fuse should have very low resistance, close to zero ohms. If the multimeter reads an infinite resistance (indicated as “OL” on some multimeters), then the fuse is blown and must be replaced.
To test a fuse, follow these steps:
1.
Set the multimeter to the ohms (Ω) setting.
2.
Touch the probes to the two terminals of the fuse.
3.
Read the display on the multimeter. If the multimeter reads zero ohms, then the fuse is good. If the multimeter reads infinity (OL), then the fuse is blown and should be replaced.
In addition to the above steps, here are some additional tips for using a multimeter to test a fuse:
| Tip | Description |
|---|---|
| Use a good quality multimeter. | A cheap multimeter may not be able to accurately measure resistance. |
| Make sure the fuse is not connected to any power source. | Testing a fuse that is connected to power could damage the multimeter. |
| Be careful not to short the probes together. | Shorting the probes together will damage the multimeter. |
Checking the Fuse Resistance
A multimeter is a versatile tool that can be used to measure the resistance of a fuse. To do this, set the multimeter to the ohms setting and touch the probes to the ends of the fuse. If the fuse is blown, the multimeter will read “OL” (open line). If the fuse is good, the multimeter will read a low resistance, typically in the range of 0 to 1 ohms.
Using a Test Light
A test light is a simple tool that can be used to quickly and easily test a fuse. To do this, connect one end of the test light to the negative terminal of a battery and the other end to one end of the fuse. If the fuse is blown, the test light will not light up. If the fuse is good, the test light will light up.
Using a Continuity Tester
A continuity tester is a specialized tool that can be used to test the continuity of a circuit. To do this, connect one end of the continuity tester to one end of the fuse and the other end to the other end of the fuse. If the fuse is blown, the continuity tester will not sound. If the fuse is good, the continuity tester will sound, indicating that there is a complete circuit.
| Fuse Type | Resistance Range (Ohms) |
|---|---|
| Automotive fuse | 0.05 – 5 |
| Household fuse | 0.1 – 10 |
| Glass fuse | 0.2 – 50 |
Testing with a Fuse Tester
Fuse testers are inexpensive, handheld devices designed specifically for testing fuses. They are easy to use and provide quick results, making them a convenient option for testing fuses in various applications. Fuse testers typically feature a light or LED indicator to indicate whether the fuse is blown or intact.
To test a fuse with a fuse tester, follow these steps:
- Set the fuse tester to the correct voltage range for the fuse you are testing.
- Insert the fuse into the designated slot or terminals on the fuse tester.
- Press the test button or trigger on the fuse tester.
- Observe the indicator light or LED. If the fuse is blown, the indicator will not light up. If the fuse is intact, the indicator will light up.
- Remove the fuse from the fuse tester and inspect it visually for any signs of damage, such as melted or broken filaments.
Fuse testers can be used to test different types of fuses, including glass fuses, ceramic fuses, and automotive fuses. Some fuse testers also feature a built-in continuity tester, which can be useful for troubleshooting electrical circuits.
| Advantages of Using a Fuse Tester | |||||
|---|---|---|---|---|---|
| -Quick and easy to use | -Provides precise results | -Compact and portable | -Affordable | -Can test different types of fuses | -Some models feature a built-in continuity tester |
Swapping with a Known Good Fuse
If you have access to a known good fuse that has the same specifications as the potentially blown fuse, you can perform a quick and reliable test.
Materials Required:
| Known good fuse |
Steps:
-
Disconnect Power: Ensure the circuit is de-energized before handling any electrical components.
-
Identify the Fuse: Locate the fuse box or panel where the blown fuse is believed to be situated.
-
Remove the Fuse: Carefully remove the blown fuse using a fuse puller or needle-nose pliers.
-
Inspect the Fuse: Examine the fuse for any visible signs of damage, such as blown wire or discoloration.
-
Insert the Known Good Fuse: Install the known good fuse into the fuse socket in place of the blown fuse.
-
Test the Circuit: Re-energize the circuit and check if the problem has been resolved. If the new fuse blows immediately or within a short time, it indicates a potential fault in the circuit or appliance.
-
Replace the Fuse (if necessary): If the known good fuse remains intact after testing, it is likely that the original fuse was blown. Replace the new fuse with a permanent fuse of the same specifications.
Inspecting the Fuse Terminal Contacts
The terminal contacts of a fuse are essential for ensuring a secure connection and proper electrical flow. To inspect them thoroughly:
- Remove the fuse: Carefully remove the fuse from the fuse holder using fuse pullers or needle-nose pliers.
- Check for corrosion: Look for any signs of corrosion or discoloration on the contacts. If there is excessive oxidation or buildup, it may impair conductivity.
- Clean the contacts (if necessary): If corrosion is present, use a fine-grit sandpaper or emery cloth to gently clean the contacts. Avoid using steel wool or sharp objects that could damage the metal.
- Inspect for damage: Examine the contacts for any signs of damage, such as cracks, dents, or burns. If severe damage is observed, replace the fuse.
- Check for looseness: Gently wiggle the fuse up and down in the fuse holder. If it moves excessively, the contacts may be loose and need to be tightened.
- Tighten the contacts (if necessary): Using a small screwdriver or a specialized fuse terminal tool, carefully tighten the screws that secure the fuse contacts. Avoid overtightening as this can strip the threads.
- Reinstall the fuse: Once the contacts are inspected and cleaned, insert the fuse back into the fuse holder and ensure it is securely fastened.
Inspecting Fuse Contacts Table
| Observation | Action |
|---|---|
| Excessive corrosion or discoloration | Clean the contacts with sandpaper or emery cloth |
| Cracks, dents, or burns | Replace the fuse |
| Loose contacts | Tighten the screws securing the fuse contacts |
Troubleshooting Faulty Fuses
Identifying Fuse Failure
If a device or circuit is not functioning properly, the first step is to check the fuses. Failed fuses can be identified by their melted or broken filaments.
Testing Fuses with a Multimeter
Use a multimeter set to the continuity setting. Touch the probes to the two terminals of the fuse. If the multimeter beeps, the fuse is good. If there is no sound, the fuse is blown.
Visual Inspection
Fuses can also be tested by visually inspecting them. Look for signs of melting or damage to the filament.
Using a Fuse Tester
Fuse testers are specialized tools designed to test fuses quickly and easily. They use a light to indicate whether the fuse is blown or not.
Fuse Specifications
It’s important to replace a blown fuse with one of the same amperage rating. Using a fuse with a higher amperage can lead to overheating and potential hazards.
Resettable Fuses
Some fuses, known as resettable fuses, can be reset after tripping. Look for a small button on the fuse to reset it.
Table of Fuse Amperage Ratings
| Fuse Color | Amperage Rating |
|---|---|
| Brown | 6 |
| Red | 10 |
| Blue | 15 |
| Yellow | 20 |
| Green | 25 |
| Purple | 30 |
| Orange | 35 |
| White | 40 |
Additional Tips
* Always turn off power before testing or replacing fuses.
* Wear safety glasses and use insulated tools.
* If you are not comfortable testing or replacing fuses, contact a qualified electrician.
* Keep a spare assortment of fuses on hand for replacement purposes.
Safety Precautions When Testing Fuses
When testing fuses, it is important to take the following safety precautions to avoid electrical shock or other injuries:
- Turn off the power to the circuit before testing the fuse.
- Use a non-conductive tool, such as a plastic screwdriver, to remove and replace the fuse.
- Do not touch the metal parts of the fuse or fuse holder with your bare hands.
- If the fuse is blown, do not attempt to repair it.
- Replace the blown fuse with a fuse of the same amperage and type.
- Do not use a fuse with a higher amperage than the one specified for the circuit.
- Never bypass a fuse.
- If you are not comfortable testing fuses yourself, consult a qualified electrician.
Visual Inspection
The first step in testing a fuse is to visually inspect it. Look for any signs of damage, such as a broken filament, scorch marks, or melted plastic. If the fuse is damaged, it should be replaced.
Continuity Test
If the fuse appears to be undamaged, you can perform a continuity test to check for electrical continuity. To do this, you will need a multimeter set to the ohms setting. Touch one probe of the multimeter to each end of the fuse. If the fuse is good, the multimeter will display a reading of 0 ohms. If the fuse is blown, the multimeter will display a reading of infinity.
Fuse Tester
You can also use a fuse tester to test fuses. Fuse testers are available at most hardware stores. To use a fuse tester, simply insert the fuse into the tester and press the button. If the fuse is good, the tester will light up. If the fuse is blown, the tester will not light up.
| Fuse Type | Amperage Range |
|---|---|
| Standard Fuse | 1-30 amps |
| Mini Fuse | 2-30 amps |
| Micro Fuse | 1-15 amps |
Follow-Up Actions after Replacing a Fuse
1. **Inspect the Circuitry:** Once the fuse is replaced, carefully examine the circuitry connected to it. Look for any signs of damage, loose connections, or potential hazards that could have caused the fuse to blow in the first place. If any issues are detected, address them promptly to prevent further problems.
2. **Test the Fuse:** After replacing the fuse, use a multimeter to verify its integrity. Connect the multimeter to the fuse terminals and check for continuity. If the multimeter shows an open circuit, the fuse is still blown and needs to be replaced again.
3. **Check for Short Circuits:** If the fuse continues to blow after replacement, there may be a short circuit in the circuit. Disconnect all devices and appliances connected to the circuit and test the fuse again. If the fuse still blows, the short circuit is likely located in the wiring or the outlet.
4. **Determine Fuse Cause:** Investigate the cause of the blown fuse. Consider factors such as power surges, excessive load on the circuit, faulty appliances, or wiring issues. Identifying the root cause will help prevent future fuse burnouts.
5. **Check Other Fuses:** If one fuse blows, it’s a good idea to check other fuses in the same circuit or panel. Blown fuses can be an indication of an underlying electrical problem that may affect multiple circuits.
6. **Tighten Connections:** Fuses can blow due to loose connections. After replacing a fuse, tighten any screw terminals or wire connections in the circuit to ensure good contact and prevent arcing.
7. **Inspect Wires:** Look for any signs of damage, frayed insulation, or discoloration on the wires connected to the fuse. Damaged wires can cause short circuits or other electrical hazards.
8. **Check Receptacles:** Inspect electrical outlets and switches connected to the circuit for any loose connections, burns, or other anomalies. Faulty receptacles can cause fuse blowouts and other electrical issues.
9. **Limit Circuit Load:** Avoid overloading circuits by plugging too many appliances or devices into a single outlet. A high power demand can cause a fuse to blow to protect the circuit from overheating.
10. **Consider Using Circuit Breakers:** As an alternative to fuses, consider installing circuit breakers in your electrical system. Circuit breakers automatically trip when an overload occurs, providing greater safety and convenience than fuses that need to be manually replaced.
| Fuse Type | Capacity |
|---|---|
| Standard Buss Fuse | 15A, 20A, 30A |
| Slow-Blow Fuse | 5A, 10A, 15A |
| Fast-Acting Fuse | 3A, 5A, 10A |
How to Test a Fuse
Using a multimeter:
1. Set the multimeter to the ohms setting.
2. Touch one probe to each end of the fuse.
3. If the multimeter reads 0 ohms, the fuse is good.
4. If the multimeter reads infinity, the fuse is blown.
Using a continuity tester:
1. Turn on the continuity tester.
2. Touch one probe to each end of the fuse.
3. If the continuity tester lights up or beeps, the fuse is good.
4. If the continuity tester does not light up or beep, the fuse is blown.
Using a visual inspection:
1. Look at the fuse for any signs of damage, such as cracks, breaks, or discoloration.
2. If you see any damage, the fuse is blown.
3. If you do not see any damage, the fuse may still be blown. You can test it using a multimeter or continuity tester to be sure.
People Also Ask
How do you know if a fuse is blown?
You can know if a fuse is blown by testing it with a multimeter or continuity tester. You can also look for signs of damage, such as cracks, breaks, or discoloration.
What happens if you replace a blown fuse with a fuse that is too big?
If you replace a blown fuse with a fuse that is too big, it can cause the circuit to overheat and start a fire. It is important to only replace a blown fuse with a fuse of the correct amperage.
How can I prevent fuses from blowing?
There are a few things you can do to prevent fuses from blowing, such as:
– Avoiding overloading circuits
– Using the correct amperage fuse for each circuit
– Inspecting fuses regularly for signs of damage
– Unplugging appliances and electronics when not in use
