How to Test a Fuse with a Multimeter – UK Plug, Car & Appliance Fuse Guide
Knowing how to test a fuse with a multimeter is one of the simplest and most useful electrical troubleshooting skills. A fuse can look perfectly normal from the outside but still be electrically open, which is why checking it with a digital multimeter is more reliable than relying only on visual inspection.
This guide explains how to test UK 13A plug fuses, 3A plug fuses, automotive blade fuses, glass fuses, ceramic fuses and appliance fuses using continuity or resistance mode. It also explains what OL means on a multimeter, how to recognise a blown fuse, and what to do if a replacement fuse blows again.
Remove or electrically isolate the fuse, set the multimeter to continuity or resistance (Ω), and touch one probe to each end of the fuse. A good fuse normally gives a beep and a very low resistance reading. A blown fuse normally gives no beep and may display OL, indicating an open circuit.
What Does a Fuse Do?
A fuse is an over-current protection device. Inside the fuse is a metal element designed to melt when too much current passes through it. When the element melts, the electrical circuit opens and current stops flowing.
This helps prevent cables, appliances, electronic equipment and vehicle wiring from overheating when there is an overload or electrical fault.
| Fuse Type | Common Application | Where to Probe |
|---|---|---|
| BS 1362 UK Plug Fuse | UK 13A plugs, appliances and extension leads. | Touch one probe to each metal end cap. |
| Automotive Blade Fuse | Cars, vans, campervans, motorcycles and 12V accessories. | Touch one probe to each metal blade after removing the fuse. |
| Glass Tube Fuse | Older electronics, power supplies and equipment. | Touch the probes to the two metal end caps. |
| Ceramic Fuse | Appliances, multimeters and electrical equipment. | Touch one probe to each conductive end. |
How to Test a Fuse with a Multimeter: Step-by-Step
Never use resistance or continuity mode on an energised circuit. Disconnect the appliance from the mains, switch off the vehicle circuit where appropriate, and remove or safely isolate the fuse before performing this test.
Step 1: Remove or Isolate the Fuse
For a UK plug fuse, unplug the appliance from the wall socket before opening the plug. For an automotive blade fuse, switch off the ignition and remove the fuse from the fuse box for a simple continuity test.
Step 2: Connect the Multimeter Leads
- Black test lead → COM socket.
- Red test lead → V/Ω measurement socket.
Do not use the 10A or mA current socket for a continuity test.
Step 3: Select Continuity Mode
Set the digital multimeter to continuity mode. This is usually shown by a sound-wave or buzzer symbol. On some meters, continuity shares a dial position with resistance or diode test.
Step 4: Test the Multimeter First
Touch the two probe tips together. A working continuity function should normally beep and display a very low resistance reading. This confirms the meter and leads are responding before you test the fuse.
Step 5: Touch the Probes to the Fuse
Touch one probe to each metal end or terminal of the fuse. Probe polarity does not matter for a simple fuse continuity test.
Step 6: Read the Result
| Multimeter Result | Fuse Condition | Meaning |
|---|---|---|
| Beep + very low resistance | Usually good | There is an electrical path through the fuse. |
| No beep + OL | Likely blown | The fuse is electrically open or the probe contact is poor. |
| Unstable/high resistance | Check again | Clean the terminals and make sure both probes have good contact. |
What Does OL Mean When Testing a Fuse?
On many digital multimeters, OL indicates that the circuit is open or the resistance is outside the meter's measurable range. When you are testing a removed fuse in resistance or continuity mode, an OL reading usually means that the fuse element has broken and there is no electrical path between its two ends.
Before declaring the fuse blown, make sure the probes are making good contact and verify the meter by touching the probes together.
How to Test a UK 13A Plug Fuse
Modern UK appliances normally use a BS 1363 plug containing a BS 1362 cartridge fuse. Common fuse ratings are 3A and 13A, while 5A fuses may still be found in some older equipment.
- Unplug the appliance from the wall socket.
- Remove the plug fuse.
- Set the multimeter to continuity.
- Touch one probe to each metal cap.
- A beep/low resistance normally indicates a good fuse; OL/no continuity indicates a blown fuse.
Replace a blown plug fuse only with the correct type and rating recommended for the appliance. Never fit a higher-rated fuse simply because the correct fuse keeps blowing.
How to Test a Car Blade Fuse with a Multimeter
Blade fuses are widely used in cars, vans, campervans, motorcycles and other 12V electrical systems. A blown blade fuse can cause headlights, radios, USB sockets, sensors, fans or other vehicle equipment to stop working.
- Switch the ignition and affected circuit off.
- Identify the correct fuse using the vehicle fuse diagram.
- Remove the blade fuse.
- Set the multimeter to continuity.
- Touch one probe to each blade.
- Beep/low resistance normally means good continuity; OL/no beep normally means the fuse is blown.
If the replacement fuse blows again, do not keep fitting new fuses. A repeated blown fuse may indicate a short circuit, failed component, damaged wiring or excessive load that needs further diagnosis.
Can a Fuse Look Good but Still Be Blown?
Yes. Some glass and automotive fuses have a visible element that can be inspected, but visual inspection is not always conclusive. Ceramic plug fuses hide the internal element completely.
A continuity test provides a more reliable answer because it checks whether electricity can actually pass from one end of the fuse to the other.
Why Does the New Fuse Keep Blowing?
A fuse normally blows for a reason. If the new fuse fails again, look for the underlying fault rather than fitting a higher-rated fuse.
| Possible Cause | Example | Next Step |
|---|---|---|
| Short circuit | Damaged cable or component causes very high current. | Stop using the circuit and diagnose the fault. |
| Overload | Connected equipment draws more current than the fuse permits. | Check equipment rating and manufacturer's instructions. |
| Component failure | Failed motor, heater, power supply or vehicle accessory. | Test the load and wiring before replacing another fuse. |
| Incorrect fuse | Wrong current rating, fuse type or physical format. | Install only the specified replacement fuse. |
Continuity Mode vs Resistance Mode for Fuse Testing
Both modes can test a fuse.
- Continuity mode: fastest for everyday testing because the meter gives an audible beep when resistance is sufficiently low.
- Resistance mode: shows the actual resistance measured through the fuse. A good fuse should have very low resistance compared with an open fuse.
For most plug and automotive fuse checks, continuity mode is the easiest option.
Common Fuse Testing Mistakes
- Testing resistance or continuity on a live circuit.
- Leaving the red test lead in the current input socket.
- Assuming a fuse is good because it looks undamaged.
- Poor probe contact causing a false OL reading.
- Replacing a fuse with a higher current rating.
- Repeatedly replacing fuses without diagnosing why they are blowing.
Which Multimeter Is Suitable for Fuse Testing?
Almost any digital multimeter with a reliable continuity or resistance function can test a disconnected fuse. For general electrical, automotive, appliance and electronics troubleshooting, a meter with fast continuity, auto-ranging and clear display makes the process easier.
The ZOYI ZT-102A 6000-count True-RMS digital multimeter includes audible continuity and resistance measurement as part of its general electrical testing functions.
Browse ZOYI Digital Multimeters
Q&A – Common Fuse Testing Questions
How do you test if a fuse is blown with a multimeter?
Remove or isolate the fuse, set the meter to continuity mode, and touch one probe to each end. A good fuse normally beeps and shows very low resistance. A blown fuse normally gives no beep and may display OL.
Should a good fuse beep on a multimeter?
Usually yes when the meter is set to continuity mode. The exact continuity threshold varies between meters, so also look for a low resistance reading.
What does OL mean when testing a fuse?
In resistance or continuity testing, OL normally means the circuit is open or beyond the resistance range. On a removed fuse, this usually indicates a blown fuse if probe contact is good.
Can a fuse look good but still be blown?
Yes. Internal damage may not always be visible, particularly with ceramic fuses. A multimeter continuity check is more reliable than visual inspection alone.
Can I test a fuse without removing it?
There are powered diagnostic methods for testing some installed fuses, particularly in vehicles, but for a simple continuity or resistance test the fuse should be removed or properly isolated so other circuit paths cannot affect the reading.
How do I test a 13A plug fuse?
Unplug the appliance, remove the BS 1362 fuse from the plug, select continuity mode and touch one probe to each end cap. A beep and low resistance normally indicate a good fuse.
Can I replace a 3A fuse with a 13A fuse?
Do not increase the fuse rating simply to stop it blowing. Use the rating specified by the appliance manufacturer or appropriate for the equipment. The fuse is there to protect the cable and appliance from excessive current.
Why does my replacement fuse immediately blow?
The circuit may have a short, overloaded component, damaged wiring or another electrical fault. Stop replacing fuses until the cause has been identified.
How do I test a car blade fuse?
Switch the circuit off, remove the blade fuse and test across its two blades in continuity mode. Beep plus low resistance normally means good continuity; OL or no beep normally indicates an open fuse.
Can I test my multimeter's own internal fuse?
Yes, but the procedure depends on the meter design. Internal current-input fuses must always be replaced with the exact specified type, current rating, voltage rating and breaking capacity.
A blown fuse is often a symptom rather than the root cause. If a fuse repeatedly fails, investigate the circuit instead of fitting a larger fuse.
Final Verdict
Testing a fuse with a digital multimeter takes only a few seconds. Remove or isolate the fuse, select continuity mode, verify the meter, and test across the two fuse terminals. A beep and low resistance normally indicate a complete fuse element, while OL and no continuity usually indicate a blown fuse.
The same basic method works for UK plug fuses, automotive blade fuses, glass fuses, ceramic fuses and many appliance fuses. The most important rules are to test with the circuit de-energised and to replace a blown fuse only with the correct specified type and rating.