How to Fix a Blown Fuse

How to Fix a Blown Fuse

A blown fuse is one of the oldest and most reliable forms of electrical protection — and one of the most misunderstood. Unlike a circuit breaker, which you can simply reset, a blown fuse must be physically replaced. But the process is straightforward once you know what to look for.

This guide covers blown fuses in home fuse boxes, appliances, and electronics.

What Causes a Fuse to Blow?

A fuse blows when too much current flows through it — the thin metal wire inside melts, breaking the circuit and stopping the flow of electricity. This protects your wiring and appliances from damage. Common causes include:

• Overloaded circuit — too many devices drawing power at once
• Short circuit — a hot wire touching a neutral wire inside an appliance or outlet
• Ground fault — a hot wire contacting a grounded surface
• Faulty appliance — an appliance with damaged internal wiring drawing excessive current
• Power surge — a sudden spike in voltage from the utility or a lightning strike

What You'll Need

• AstroAI Digital Multimeter — test fuses for continuity to confirm which one has blown, and verify voltage after replacement.
• Klein Tools NCVT1P Non-Contact Voltage Tester — confirm power is off at the fuse box before touching anything.
• 300Pcs 5x20mm Glass Fuse Assortment (250V) — a comprehensive kit covering 15 common ratings (0.1A to 20A) for appliances and electronics. Always replace with the exact same amperage rating.
• Fuse puller or needle-nose pliers (for cartridge fuses in a fuse box)
• Flashlight

Part 1: How to Fix a Blown Fuse in a Home Fuse Box

Older homes (typically pre-1960s) may have a fuse box instead of a circuit breaker panel. Fuse boxes use either plug fuses (screw-in) or cartridge fuses (cylindrical, pull-out).

Step 1: Cut Power and Locate the Fuse Box

Your fuse box is usually in a utility room, basement, or hallway. Before opening it, use your non-contact voltage tester to check the area. Turn off or unplug devices in the affected area to reduce the load before replacing the fuse.

Step 2: Identify the Blown Fuse

Open the fuse box and inspect each fuse:

• Plug fuses (screw-in): Look through the small glass window. A blown fuse will show a broken or melted wire inside, or the window may be discolored/blackened.
• Cartridge fuses: You can't always see the damage visually. Use your multimeter set to continuity mode — a good fuse will beep; a blown fuse will show no continuity.

Step 3: Remove the Blown Fuse

• Plug fuse: Unscrew it counterclockwise. Do not touch the metal contacts — use the insulated rim only.
• Cartridge fuse: Use a fuse puller tool or needle-nose pliers to pull it straight out of the clips. Never use bare hands on a cartridge fuse that may still be energized.

Step 4: Match and Replace

This is the most important step: always replace a fuse with the exact same amperage rating. Installing a higher-rated fuse (e.g., replacing a 15A fuse with a 20A) defeats the protection and is a serious fire hazard.

Check the amperage printed on the old fuse, then select the matching replacement from your glass fuse assortment kit. Screw in or push in the new fuse firmly.

Step 5: Restore Power and Test

Close the fuse box. Restore power to the area and test outlets or lights. If the fuse blows again immediately, there's an underlying fault — a short circuit or faulty appliance — that needs to be diagnosed before replacing the fuse again.

Part 2: How to Fix a Blown Fuse in an Appliance

Many appliances — microwaves, TVs, power strips, coffee makers, and more — have internal fuses that protect their electronics. When an appliance suddenly stops working with no other obvious cause, a blown internal fuse is often the culprit.

Step 1: Unplug the Appliance

Always unplug the appliance completely before opening it. Even with the power switch off, internal components may retain charge.

Step 2: Locate the Fuse

Consult the appliance's manual or search online for the fuse location. Common locations include:

• Near the power cord entry point
• On the main circuit board
• In a dedicated fuse holder on the back panel

Step 3: Test the Fuse

Remove the fuse and test it with your multimeter set to continuity mode. Touch one probe to each end of the fuse — a good fuse beeps; a blown fuse shows no continuity (open circuit).

Step 4: Replace with Exact Match

Note the fuse's amperage, voltage rating, and physical size (most appliance fuses are 5x20mm). Select the matching fuse from your glass fuse assortment — the kit covers 15 values from 0.1A to 20A at 250V, which handles the vast majority of household appliance fuses.

Install the new fuse, reassemble the appliance, and test.

Never Do This With Fuses

• Never install a higher-amperage fuse than the original — this is the #1 fuse safety mistake and a leading cause of electrical fires.
• Never use a coin, foil, or wire to bypass a blown fuse — this removes all protection from the circuit.
• Never replace a fuse without reducing the load first — if the circuit was overloaded, the new fuse will blow immediately.
• Never ignore a fuse that blows repeatedly — it's a symptom of an underlying problem that needs to be fixed.

Fuse vs. Circuit Breaker: What's the Difference?

Frequently Asked Questions

How do I know if a fuse is blown without a multimeter?

For glass plug fuses in a fuse box, look through the glass window — a blown fuse will show a broken wire or blackened/cloudy glass. For cartridge fuses and appliance fuses, visual inspection is unreliable — a multimeter continuity test is the only reliable method.

Can I replace a 15A fuse with a 20A fuse?

No — never. The fuse rating must match the circuit's wiring capacity. Installing a higher-rated fuse allows more current to flow than the wiring can safely handle, which can overheat the wires and cause a fire.

Why does my fuse keep blowing?

A fuse that blows repeatedly indicates an underlying problem: an overloaded circuit, a short circuit in the wiring, or a faulty appliance. Identify and fix the root cause before replacing the fuse again. The same causes that make circuit breakers trip repeatedly also apply to fuses — check for overloaded circuits, short circuits, or faulty appliances.

Should I upgrade from a fuse box to a circuit breaker panel?

If your home still has a fuse box, upgrading to a modern breaker panel is worth considering — especially if the panel is old, the fuses blow frequently, or you're adding new circuits. This is a job for a licensed electrician and typically costs $1,500–$4,000.

Quick Recap

1. Cut power and locate the fuse box or appliance fuse
2. Identify the blown fuse visually or with a multimeter continuity test
3. Remove the blown fuse safely
4. Replace with the exact same amperage rating — never higher
5. Restore power and test — if it blows again, find the root cause

Keep a glass fuse assortment kit and a digital multimeter on hand — together they cover virtually every fuse replacement scenario in the home.

Disclosure: This post contains affiliate links. If you purchase through these links, we may earn a small commission at no extra cost to you. We only recommend products we trust.