How to Test Screw-in Plug Fuses

The plug fuse is one of the most common and simplest electrical components found in homes and businesses.

It’s a device that, when overloaded or short-circuited, will break the circuit to avoid damage to your equipment.

But how do you know if it needs replacing? And how do you test it? Let’s take a look.

What are plug fuses?

Plug fuses, also known as cartridge fuses, Screw-in Fuses (SIF), or plug-in fuses, are inserted into a socket to protect an electrical circuit. They are commonly used in household appliances and electronics. Plug fuses come in various ratings, depending on the amount of current that they can safely handle.

Types of plug fuses:

There are two types of plug fuses- the Edison base (screw-in) fuse and the bayonet mount (twist-and-pull) fuse. The Edison base fuse has a threaded metal cap that screws into a socket, while the bayonet mount fuse has a plastic cap that twists into place.

Both types of fuses are designed to protect electrical circuits from overloads. The size of the fuse determines the amount of current that can flow through it before it blows. In general, larger fuses can handle more current than smaller ones.

For example, a 15-amp fuse will allow up to 15 amps of current to flow through it before blowing, while a 20-amp fuse will allow up to 20 amps of current to flow through it. Fuses are available in various sizes, so it is important to choose the right size for the circuit you are trying to protect.

It’s important to test it regularly to ensure that your plug fuse is working properly. Here’s how: 

1. Look at the fuse to see if it has blown:

If you think you may have blown a fuse, you should first check the fuse box. Most homes have a main fuse box containing all the house’s fuses. Once you find the fuse box, look at the fuse to see if it has blown. A blown fuse will have a broken or blackened wire inside it. If the fuse looks damaged, replace it with a new one. It’s important to note that not all fuses are the same, so be sure to replace the fuse with one with the same amperage. Once you’ve replaced the fuse, flip the switch to see if power is restored. If not, you may have a more serious electrical problem and should call an emergency electrician.

2. Check the continuity of the fuse with a multimeter:

When a circuit isn’t working, it could be because of several different issues. However, one common problem is a blown a fuse. Fuses are designed to “blow” or break when too much current flows through them. It protects the wiring in your home from overheating and catching fire. To test if a fuse is blown, you can use a multimeter.

First, set your multimeter to the “continuity” setting. Then touch the meter’s probes to the two metal terminals on the fuse. If the meter beeps or lights up, the fuse is good. If not, then the fuse is blown and needs to be replaced. Testing fuses with a multimeter is a quick and easy way to narrow down why a circuit isn’t working.

3. Test the fuse by using it to protect a circuit:

When testing a fuse, it’s important to Hook It Up to an electrical circuit and turn on the power to the circuit before anything else. If the fuse blows, then that means it’s working properly. However, if the fuse doesn’t blow, there might be a problem with the fuse itself or the circuit. If you’re unsure which one it is, you can try testing the fuse again with a different circuit. That way, you can narrow down where the problem might be. Once you’ve found the problem, you can figure out how to fix it. And that’s how you test a fuse!

Tips for preventing screw-in plug fuses from blowing

Use the correct size and type of fuse:

As any electrician knows, fuses are essential for protecting circuits from overloads. If too much current flows through a circuit, it can cause serious damage to the wiring and components. Fuses are designed to break the circuit if the current exceeds a certain level, preventing the damage from occurring. However, it’s important to use the correct size and type of fuse for the circuit you’re trying to protect. Using a fuse with too high of a rating can damage the circuit due to over current, while using a fuse with too low of a rating can allow an over current condition to occur without interrupting the flow of current. As a result, it’s essential to select the correct fuse for the job at hand.

Don’t use a higher-rated fuse:

Using a fuse with a higher rating than specified for the circuit can be dangerous. If the fuse is rated for a higher current than the circuit, it may not trip when there is an overload, potentially leading to a fire. 

Regularly check the wiring in the circuit:

One of the most common causes of screw-in plug fuses blowing is damaged or frayed wiring. Over time, exposure to heat, humidity, and other elements can cause the insulation on wires, making them more susceptible to damage. If you live in an older home, it’s especially important to regularly check the wiring in your circuits. Even if the wires look in good condition, it’s good to have an electrician check them to be safe.

Upgrade the electrical system:

If you’re the proud owner of an older home, there’s no doubt that you’ve put a lot of effort into maintaining its original character. However, it’s important to remember that your home’s electrical system may not be able to keep up with the increased demand for power that comes with today’s appliances. In particular, screw-in plug fuses are notorious for blowing out when overloaded. To prevent this from happening, it’s a good idea to have your electrical system upgraded by a qualified emergency electrician. This way, you can rest assured that your home is safe and compatible with your modern conveniences.

Keeping your plug fuses in good working order is important for maintaining a safe and functional electrical system in your home. With regular maintenance, you can help prevent blown fuses and keep your home’s electrical system running smoothly.

Final lines:

Screw-in plug fuses are an important part of any electrical system, and it is important to test them regularly by emergency electricians to ensure that they are working properly. Testing your screw-in plug fuses regularly is a good way to ensure that they are working properly. By doing so, you can help prevent electrical accidents in your home or office.


How often should I check my screw-in plug fuses?

It is generally recommended that you check your screw-in plug fuses every three months. However, if you live in an older home or office, it is good to check them more frequently.

What are some signs that a fuse is blown?

Some signs that a fuse is blown include a burning smell, a visible break in the metal wire, or a discolored fuse. If you notice any of these signs, it is important to replace the fuse as soon as possible.

Can I use a higher-rated fuse than what is specified for the circuit?

You should never use a higher-rated fuse than what is specified for the circuit. Using a fuse with a higher rating than specified for the circuit can be dangerous.

How can I prevent my screw-in plug fuses from blowing?

Some tips to prevent your screw-in plug fuses from blowing include using the correct size and rating for the circuit, regularly checking the wiring, and upgrading the electrical system if you live in an older home.

Are all plug fuses the same?

No, all plug fuses are not the same. There are different plug fuses, including screw-in, cartridge, and push-button. Choosing the right type of fuse for your electrical system is important.


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