Here’s How to Tell if a Fuse Is Blown

If a system or appliance in your home suddenly stops working, there's a chance that you've blown a fuse or tripped a circuit. Knowing how to tell if a fuse is blown can save you from many potential headaches down the line. 

To make it easier for you to diagnose the problem, we're sharing everything you need to know about how to tell if a fuse is blown, what caused it, and what to do about it. 

What Does a Blown Fuse Look Like?

Blown fuses give some fairly obvious visual indicators, which help homeowners get to the bottom of things. Start by finding your fuse box, which is usually in the garage or basement, and opening it up. Look for the glass containers that hold the fuses.

If the inside of the fuse matches any of these descriptions, it’s likely blown:

• Visible gap in the wire

• Dark or metallic-colored smear

• Cloudy or blackened appearance

• Visible signs of damage

• Broken or cracked

7 Signs You Have a Blown Fuse

Beyond performing a visual inspection, blown fuses make their presence known all throughout your home’s electrical grid. Here are some tell-tale signs that some of your fuses have reached the point of no return.

1. There's a Short Circuit

A short circuit is a kind of electrical fault. Typically, electrical faults occur when an electrical current moves outside of the path it's intended to follow (aka the circuit) because it doesn't have enough resistance from things like insulation or the circuit breaker itself. When this current veers from its path, it can overload nearby wires, creating a short circuit. 

Often, a short circuit causes sparks or even smoke or flames. You may also hear a crackling sound. This process can damage or even destroy the devices the circuit is connected to. When it happens, you should immediately unplug the faulty device and inspect the outlet for damage. If you see damage, you should contact an electrician to come in and fix it.

2. There's a Ground Fault

Ground faults are a type of short circuit. They occur when the current-carrying wire touches a grounded system, like a grounded metal wall box or a grounded part of an appliance. In this case, "grounded" simply means a part of the system is touching the earth. 

During a ground fault, too much current flows through unintended pathways, which can damage the systems the current is connected to. Unlike the standard short circuit described above, you're not likely to hear cracking sounds or see sparks or flames, but you might see strobing lines on a computer or television. 

A ground fault can shock you when you touch surrounding outlets and devices, so you should stay clear from the affected area and call a local emergency electrician. 

3. Your Electrical Outlets Are Damaged 

Like many other systems in the home, electrical outlets have a certain lifespan. They may stop working due to damage or simply because they're outdated. Faulty electrical outlets can lead to a power surge, aka a power fault, which can blow a fuse or, more commonly, trip a circuit. 

Signs of a damaged outlet include burn marks, melting, chips, and cracks. A damaged outlet may also feel warm to the touch. If you suspect your outlet is damaged, then your best bet is to have a professional come in and inspect it. And if one outlet is giving you trouble, then other outlets may be faulty as well, so it's a great idea to ask the professional to inspect all of your outlets for potential problems just to be on the safe side.

4. Your Wiring Is Damaged

Similarly to damaged electrical outlets, damaged wiring can cause power surges and trip your circuits. However, it's much tougher to spot damaged wiring since it's usually hidden behind your walls. 

If you think you may have damaged wiring, then you can listen for buzzing noises, look for dimming lights, and search for any discoloration or smoke. Your wall outlets may also feel warm or vibrate to the touch. Damaged wiring can be tricky to find and fix, so you probably want to call in a professional to safely repair it. 

5. Your Circuit Is Overloaded

If you plug too many devices into a power strip or you heavily use a certain appliance, like your microwave, then the circuits they're connected to can become overloaded and trip. In this case, you should unplug the devices from the power strip or your appliance, depending on the issue, then head to your circuit breaker and flip the associated circuit switch back on. 

To prevent it from happening again, you'll want to move some of the plugs in your power strip to another outlet. But if it's a single appliance causing the problem, then unplugging that appliance whenever it's not in use can help. 

6. You Have the Wrong Fuse Type 

Fuses may look similar, but there are plenty of designs, amperages, and sizes. In other words, it is all too easy to accidentally insert an incorrect fuse, which leads to all kinds of problems with your electrical system down the line. At best? The fuse blows, requiring replacement. At worst, that fuse damages the circuit, requiring costly repairs, or leads to a fire. Open the fusebox and take a look at the fuses. Do any look out of place? If so, call a professional, as you shouldn’t attempt to remove incorrectly-sized fuses on your own. 

7. Your Electrical System Is Outdated

Modern technology means that many of us are using more electricity than ever before. This influx in use can overload electrical systems that just weren't designed for how much electricity many households use today. 

A telltale sign of this problem is that your circuits trip regularly, but you don't observe any of the issues mentioned above, like damaged outlets or wiring. If this is the case in your home, you'll either need to reduce the amount of electricity your household uses daily or call a pro to come update your system. 

How to Test for a Blown Fuse

Many blown fuses look the part, with obvious cracks and grey metallic ash inside. However, some blown fuses look perfectly fine. Additionally, many fuses are not transparent so you can’t even see inside. How do you test them in that case? It’s time to break out the multimeter. These handy tools measure AC and DC voltage, electrical resistance, and current flow. Here is an easy way to use a multimeter to test any suspicious fuses.

1. Turn off any power leading to the circuit box from the main breaker. As an added safety precaution, wear rubber gloves and stand on a rubber mat before removing the fuses.

2. Remove any fuses you want to check. To remove a fuse, just pull it out of the slot (this is why the gloves come in handy, as does shutting off the power). 

3. Turn the dial on the multimeter so it is set to “continuity.” You can use the Ohm setting here but this is the quicker option. 

4. Before testing the fuses, put the positive and negative leads together and listen for a beep. This indicates that the multimeter is functioning properly. 

5. Put each lead on either side of the fuse. Fuses are simple, containing just a single wire, so it does not matter which lead goes where. Positive, negative, it’s all the same to a fuse. 

6. Hold the leads against the fuse and listen for continuous beeping, as this indicates a fuse is in good working order. If you don’t hear anything at all, or only sporadic beeping, the fuse is blown.

7. If you are using a digital multimeter, receiving a reading of “OL”, “Open, or “Not Complete,” or getting no reading at all indicates a blown fuse. 

8. Rinse and repeat, as a standard fuse box contains anywhere from six to 12 fuses, or more in some cases.

How to Fix a Blown Fuse

You can’t fix a blown fuse. Once it’s blown, it’s dead. However, it is simple to replace the blown fuse with a shiny new one. Here’s how to replace a blown fuse, step-by-step.

1. Perform visual inspections and a multimeter test to find which fuses require replacement. Follow the steps above. 

2. Unplug appliances associated with the fuses-in-question before moving on. In other words, if the fuse provides power to part of the kitchen, for instance, unplug those fixtures. 

3. Turn the main power off to the fuse box to prevent any dangers of electric shock. 

4. Don a pair of protective rubber gloves, to be extra safe, and manually remove the blown fuses. They pop right out. 

5. Do not lose the fuses. Instead, bring them with you to the hardware store to ensure you get the correct replacements. If you are shopping online, make sure the size and voltage are correct. Feel free to buy a few spares for later on. Packs containing three fuses cost around $5 to $10. 

6. Screw the new fuse in by hand. It should go right in with no resistance. 

7. Turn on the power to the fuse box and, if you have one, use a voltage tester on any power outlets receiving current from the newly-replaced fuses. Just insert the tester leads into an outlet slot and look for a light, thus indicating power is running to the outlet. 

8. Plug your appliances, lights, and gadgets back in and power them on. Go slowly here to avoid overwhelming the fuse. Turn on one or two things, wait a few minutes, and go for one or two more. 

9. If the fuse immediately blows again, it is time to call up a local electrician to figure out what is really going on.