How to Tell if a Fuse Has Blown

A blown fuse can cause power loss in your home or electrical devices. Fuses are designed to protect electrical circuits by breaking the connection when too much current flows through them. But how can you tell if a fuse is blown?

This guide will walk you through the common causes of blown fuses, how to check for one, and what to do if you need to replace it.

6 reasons you might have a blown fuse

Fuses can blow for several reasons, and identifying the cause helps prevent future failures. Here are some of the most common:

1. Overloaded circuit

Plugging too many electrical devices into one circuit can exceed its capacity, causing the fuse to blow. If this happens frequently, you may need to redistribute your appliances or upgrade your electrical panel.

2. Short circuit

A short circuit occurs when live wires come into direct contact with each other or with the ground. This creates a surge of electricity that can instantly blow a fuse.

3. Power surges

Sudden voltage spikes, often caused by lightning or issues in the power grid, can overwhelm a fuse and cause it to blow.

4. Faulty appliances

A malfunctioning electrical device may draw more power than usual, triggering a blown fuse. If a particular circuit keeps blowing, check the devices plugged into it.

5. Faulty wiring

Loose, corroded, or damaged wiring can lead to irregular electrical currents that blow fuses. If you suspect faulty wiring, contact an electrician.

6. Incorrect fuse type

Using a fuse with the wrong amperage rating for a circuit can lead to repeated failures. Always replace fuses with the correct type and rating.

How to check if a fuse is blown

A blown fuse usually results in the loss of power to a specific area or device. To confirm, follow these steps:

1. Turn off the power – Before handling fuses, switch off the power supply at the electrical panel to avoid electric shocks.
2. Locate the fuse box – Most fuse boxes are found in basements, garages, or utility rooms.
3. Identify the affected fuse – Look for fuses labelled with the corresponding circuit.
4. Inspect the fuse visually – A blown fuse often has a darkened or broken metal wire inside its casing.

What does a blown fuse look like?

A blown fuse will typically show one or more of the following signs:

• A broken filament – The thin metal wire inside the fuse may appear broken or melted.
• Burn marks or discolouration – A black or cloudy residue inside the fuse indicates overheating.
• No continuity – If unsure, testing with a multimeter can confirm whether the fuse is still working.

Test with a multimeter

Using a multimeter is the most reliable way to check if a fuse is blown. A visual inspection can sometimes be misleading, so testing for continuity ensures an accurate result. Follow these steps to test a fuse properly:

1. Switch off the power – Before handling any electrical components, turn off the current at the mains or disconnect the appliance to prevent electric shock.
2. Remove the fuse – Carefully take the fuse out of the fuse box, electrical panel, or fuse holder cap using a fuse puller or needle-nose pliers.
3. Set the multimeter – Turn your multimeter to the continuity setting (⏸) or resistance mode (Ω).
4. Check the probes – Touch the positive and negative probes together to confirm the multimeter is working. You should hear a beep or see a reading on the display.
5. Test the fuse – Place one probe on each end of the fuse. It doesn’t matter which end connects to the positive or negative terminal.
6. Check the reading:
   • If the multimeter beeps and shows a low resistance value, the fuse is intact.
   • If there is no beep and the screen displays "OL" (overload) or infinite resistance, the fuse is blown.

Alternative resistance test

You can also test a blown fuse by using the resistance setting on the multimeter:

• A working fuse should have a resistance close to zero ohms.
• A blown-out fuse will display an infinite resistance reading or OL (open loop), meaning the circuit is broken.

Testing with a multimeter is a quick and foolproof method to determine if a fuse has blown. If you confirm the fuse is faulty, you’ll need to replace the blown fuse with a new fuse of the correct amperage rating to restore power.

What should you do if a fuse blows?

When a fuse blows, it’s usually a sign that the electrical circuit has experienced an overload, short circuit, or power surge. The first step is to identify what caused the fuse to blow before replacing it.

Check whether you've recently plugged in a faulty appliance, overloaded a particular circuit, or experienced a power surge. Once you’ve addressed the potential cause, you can replace the blown fuse safely.

Is a blown fuse easy to fix?

In most cases, replacing a blown fuse is simple. However, if fuses keep blowing, it suggests an electrical issue that needs investigation. If you experience repeated fuse failures, it’s best to call a professional to diagnose and fix the problem safely.

How to change a blown fuse in your home

1. Turn off the power supply
   • Before handling any electrical components, switch off the power at the mains to avoid the risk of electric shock.
   • If your home uses a circuit breaker instead of a fuse box, check if the breaker has tripped instead of replacing a fuse.
2. Identify the blown fuse
   • Open the fuse box cover and look for a blown fuse. It will usually appear burnt, with a broken filament inside.
   • If unsure, use a multimeter to test for continuity.
3. Remove the blown fuse
   • Use a fuse puller or needle-nose pliers to carefully extract the faulty fuse from the fuse holder cap.
   • Be gentle to avoid damaging the surrounding electrical wiring.
4. Insert a new fuse
   • Replace the blown fuse with a new fuse of the same amperage rating (e.g., 5A, 10A, or 13A).
   • Never use a fuse with a higher rating, as this could cause fire hazards or damage the electrical system.
5. Turn the power back on and test
   • Restore power by switching the mains back on.
   • Check if the affected electrical circuit or appliance is now working properly.
   • If the fuse blows again, there may be an underlying electrical fault that requires professional attention.

When to call in a JustFix professional

While replacing a single fuse is usually straightforward, repeated failures or complex electrical faults require expert help.

JustFix’s network of electricians can:

• Diagnose and fix persistent electrical faults.
• Upgrade your fuse box or circuit breakers for better protection.
• Identify and repair faulty wiring or overloaded circuits.

If your fuses keep blowing or you’re unsure how to fix an issue, book a trusted electrician through the JustFix app or website today to restore power safely and efficiently.

For more help with your electrics, read our handy guides on how to read your electric meter, PAT testing, and more.

FAQs

What's the difference between a fuse and a circuit breaker?

A fuse and a circuit breaker both protect electrical circuits from overloads and short circuits, but they work differently. A fuse contains a thin metal wire that melts when excessive current flows through it, permanently breaking the circuit. Once a fuse blows, it must be replaced.

A circuit breaker, on the other hand, is a reusable switch that automatically trips when it detects a fault. Instead of melting, it interrupts the current flow and can be manually reset after the issue is resolved.

While fuses react faster and are generally cheaper, circuit breakers offer convenience and can handle repeated faults without needing replacement.

How can you tell if a fuse is tripped?

You can tell if a fuse is tripped by checking your fuse box or circuit breaker panel. If a circuit breaker has tripped, its switch will be in the ‘off’ or middle position. For older fuse boxes, a blown fuse may have a broken filament or appear blackened.

To reset a tripped breaker, switch it fully off and then back on. If the fuse keeps tripping, it may indicate an electrical fault that requires professional inspection.