A fuse is a safety device that breaks an electrical circuit when too much current flows through it

When a fuse blows, it stops electricity from reaching whatever is plugged into that circuit — a light, an outlet, a appliance. The fuse itself is a small cylinder or cartridge with a metal filament inside. When current gets too high, that filament melts and the circuit breaks. A meter is a handheld tool that measures electrical properties: voltage (the push of electricity), current (the flow), and resistance (how much something blocks the flow).

To check whether a fuse is blown, you use a meter set to measure resistance. A good fuse shows low resistance — electricity can flow through it easily. A blown fuse shows infinite or very high resistance — the filament is broken and no electricity can pass. This takes about two minutes and requires only the meter itself.

Key Takeaways

  • A blown fuse has a broken filament inside and will show infinite resistance on a meter, while a good fuse shows very low resistance.
  • Set your meter to the ohms setting (Ω symbol) before testing, and choose the lowest ohms range available on your meter.
  • Touch one meter probe to each end of the fuse and read the number on the display — zero or near-zero means the fuse is good.
  • Always remove the fuse from the holder before testing it, and never test a fuse while it is still in the circuit.
  • If a fuse blows repeatedly, the problem is not the fuse itself but something drawing too much current on that circuit.

What you need before you start

You need a multimeter — the most common type of meter for home use. A multimeter measures voltage, current, and resistance all in one tool. You can buy one at any hardware store or online for between $15 and $50. A basic model works fine for checking fuses; you do not need an expensive one.

You also need to physically remove the fuse from its holder. Fuses sit in a fuse box or fuse panel, usually in a basement, garage, or utility closet. The fuse pulls straight out — no tools needed. If you are not sure which fuse controls the circuit you are testing, look for a label inside the fuse box door or on the panel itself. If there is no label, you may need to turn off each fuse one at a time until the circuit you are testing goes dead.

Setting your meter to measure resistance

Turn on your multimeter. Look for a dial or button labeled with the ohms symbol: Ω. This is the resistance setting. Turn the dial to the ohms position, or press the button if your meter has buttons instead of a dial.

Most meters have multiple ohms ranges — usually 200Ω, 2kΩ, 20kΩ, 200kΩ, and 2MΩ. Start with the lowest range, which is 200Ω. This gives you the most precise reading for a fuse, which has very low resistance when it is good. If your meter shows "1" or "OL" (overload) on the display, the resistance is too high for that range — switch to the next higher range and try again.

Testing the fuse

Hold the fuse in one hand. Take the two probes from your meter — one red, one black — and touch one probe to each end of the fuse. It does not matter which probe touches which end. Press firmly so the probe tips make good contact with the metal ends of the fuse.

Look at the display on your meter. A good fuse shows a reading very close to zero — usually between 0 and 5 ohms. The exact number depends on the fuse type and the meter, but anything in that range means the fuse is working. A blown fuse shows "1" or "OL" on the display, which means the resistance is too high to measure — the filament is broken and no current can flow.

If you see a reading between 5 and 50 ohms, the fuse is borderline. It may still work, but it is starting to degrade. If you see this reading and the circuit keeps having problems, replace the fuse anyway.

What to do if the fuse is blown

If the meter shows infinite resistance, the fuse is blown and needs to be replaced. Buy a replacement fuse with the same amperage rating — the number is printed on the fuse itself, usually 15A, 20A, or 30A. Never use a fuse with a higher amperage, because it will not blow when it should and you risk damaging wiring or starting a fire.

Screw or push the new fuse into the empty holder until it sits flush. The circuit should now work again. If the new fuse blows within a few days or weeks, the problem is not the fuse — something on that circuit is drawing too much current. This could be a faulty appliance, a short circuit in the wiring, or too many devices running at once. In this case, stop replacing fuses and call an electrician.

Why a fuse blows in the first place

A fuse is designed to blow when current exceeds its rating. A 15-amp fuse blows when more than 15 amps flow through it. This happens for three reasons: an appliance is faulty and drawing too much current, too many appliances are running on the same circuit at once, or there is a short circuit in the wiring.

A single blown fuse is usually not a problem — replace it and move on. But if the same fuse blows repeatedly, or if multiple fuses blow in a short time, the circuit itself has a problem. Do not keep replacing fuses. Unplug devices on that circuit one at a time and see if the fuse stops blowing. If it does, the last device you unplugged is faulty. If the fuse keeps blowing even with everything unplugged, the wiring has a short and you need an electrician.

Common mistakes when testing a fuse

The most common mistake is testing a fuse while it is still in the holder. The meter may give a false reading because it is measuring the resistance of the entire circuit, not just the fuse. Always remove the fuse first.

Another mistake is using the wrong meter setting. If you set the meter to voltage or current instead of resistance, you will get a meaningless reading or damage the meter. Always check that the dial is on the ohms (Ω) setting before you start.

A third mistake is replacing a blown fuse with one that has a higher amperage. This seems like a quick fix — a 20-amp fuse will not blow as easily as a 15-amp fuse — but it defeats the purpose of the fuse. The fuse is there to protect the wiring. If you use a fuse rated too high, the wiring can overheat and catch fire before the fuse blows.

Frequently Asked Questions

Can I test a fuse without removing it from the holder?

No. Testing a fuse while it is in the circuit gives an inaccurate reading because the meter measures the entire circuit, not just the fuse. Always remove the fuse from the holder first, then test it with the meter probes touching both ends of the fuse.

What does it mean if the meter shows a number between 0 and 5?

That means the fuse is good. A fuse with very low resistance — close to zero ohms — allows electricity to flow through it freely. Any reading between 0 and 5 ohms is normal for a working fuse. If the reading is higher than that, the fuse is degrading or blown.

Is it safe to replace a fuse with a higher amperage one?

No. Always use a fuse with the same amperage rating as the one you are replacing. A higher-rated fuse will not blow when it should, and the wiring can overheat and catch fire. The fuse rating is printed on the fuse itself — match it exactly.

What if my meter shows "OL" when I test the fuse?

"OL" means overload — the resistance is too high to measure on that range. This usually means the fuse is blown. Try switching to a higher ohms range on your meter to confirm. If the reading is still "OL" on the highest range, the fuse is definitely blown and needs to be replaced.

Why does the same fuse keep blowing?

A fuse that blows repeatedly means something on that circuit is drawing too much current. Unplug devices one at a time to find the faulty one. If the fuse keeps blowing even with everything unplugged, the wiring has a short circuit and you need an electrician to inspect it.