Fuses are electronic components that serve as a failsafe in case that an electric circuit overloads. We can find fuses in almost every household appliance and in the breaker box, the main control point for electric energy, which every house has. Fuses can also be found in multimeters.
This article will provide you with information on how to test a fuse with a multimeter, regardless of the type of fuse.
But, before we begin, I will explain what fuse types exist, since they can differ by design a lot.
I will focus on fuses that are more common in everyday life since you are more likely to come in contact with them, but all fuses can be tested in the same way. Fuses can be divided by the type of current they are used with.
They are simply called AC and DC fuses. Some fuses can be used one time only, while other fuses can be reusable.
This fuse type is the type everyone thinks about when someone says the word ‘fuse.’ Cartridge fuses are almost always cylindrically shaped. They can be made out of glass or ceramics.
This fuse type can withstand a certain amount of current before breaking down. This is called the ‘breaking capacity,’ and it should always be higher than the amount of power that flows through the circuit.
The cylinder is fixed between two metal caps on each side, and their inside is made of mostly empty space. Once they overload, the wire inside them will melt, making it impossible for the currency to flow to the other side, thus breaking the circuit.
Cartridge fuses are divided into two types: general purpose fuse and time delay fuse. Both types of cartridge fuses can be bought in 250 V and 600 V variants.
If you are not sure which type of cartridge fuse according to voltage have you bought, you can check it on one of the caps on fuse ends. Cartridge fuses can be found in multimeters, stereos, TVs and almost every other household appliance.
Automotive fuses can be found, as the name says, inside the car. They can primarily be found underneath the driving wheel and near the stereo and window raising mechanisms. Automotive fuses are also called HRC fuses, or High Rupturing Capacity Fuses. That name is derived from their purpose.
HRC fuses are able to withstand high current for a set amount of time. In case that the problem with the current isn’t removed in time, the fuse will blow out and protect your car from damage. Automotive fuses can be made from metal and ceramics, or more commonly, from metal and glass.
It is very easy to spot and recognize automotive fuses since they are usually colored very brightly, and there is never just one on the circuit board. They work in the same way as other fuses do.
The currency comes in through one terminal, and when the power becomes too high, the fuse melts down and permits the current to continue to flow through. The maximum amount of power that one automotive fuse can handle is thirty-two volts of direct current.
Automotive fuses have a considerable advantage when it comes to other types of fuses since they do not deteriorate with age. Due to their low reaction time and affordability, HRC fuses are an excellent choice for many car manufacturers.
Power fuses can be found inside fuse boxes in the house. This type of fuse can handle very high currencies.
Power fuses can come in all sorts of shapes and sizes so I won’t attempt to describe their appearance here. They are made to be durable and to have high work expectancy.
A power fuse will become active in the case that the household grid overloads, for example, in case that thunder has hit the electric pole in front of the house and the current reaches the house. This fuse type is perhaps the most important one because it can protect your life and your home.
Testing the fuse using a multimeter
In case that you are new in DIY, any multimeter will do for this, and you should use standard multimeter probes.
You need to set the multimeter to continuity setting.
We test fuses using the continuity mode because the main concept when it comes to how fuses work is continuity. If a multimeter detects no continuity, you know that the fuse is broken.
This can happen because a fuse served its purpose and burned out, thus breaking the continuity, or it is possible that due to age or due to force (in case that the fuse fell or took a hit) the string or wire inside the fuse broke.
Locate the terminals
All fuses have two terminals, positive and negative one.
The terminals are either located on the sides or the ‘legs’ of a terminal ‘stick out.’ In either way, you need to locate the positive and negative sides of the terminal before we begin testing.
Test the fuse
Once you have located the poles, take the probes and place them on the negative and positive sides of the fuse. If you hear a beeping sound and see a sign on the screen of your multimeter, you know that the fuse is in working condition.
If nothing happens, make sure that you have placed the probes on the correct sides of the fuse, and that you are maintaining pressure constantly while measuring. If there is still no sound heard, the fuse is broken, and you need to replace it.
When it comes to transparent glass fuses, it is sometimes not even necessary to test them. All that you need to do in this case is to look inside. If you see that a part of the glass is burnt up, this means that the fuse did its job.
If you look through the glass and see that the string is broken, make sure that you got the right angle, and if the string still seems broken, the fuse is inoperable.
When it comes to the second case, I would still test them with the multimeter, though. The second case is more common when fuses break under the influence of some kind of force, while the first case is possible only in situations where the fuse had melted down.
How to test the fuse with a clamp meter
Prepare the clamp meter
If you want to test your fuse with a clamp meter, the process is the same.
- First of all, you need to make sure that your clamp meter has a continuity setting and that is able to use standard multimeter probes.
- After that, it is necessary to remove the fuse from where it is located and prepare it for testing.
- Check the back side of the fuse for current ratings.
- Test the probes by snapping them one or two times against one another.
Conduct the test
Take the probes, place the positive probe on the positive pole of the fuse, and take the negative probe on the negative pole of the fuse.
If your clamp meter shows you a visual or auditory indication of continuity, the fuse works fine. If you don’t hear anything, check the fuse and make sure that you placed the probes on correct places on the fuse.
- You should always wipe the end caps on the fuse with a piece of cloth.
- In case that the fuse is an older one and that was in use for a significant time, the dirt can seriously mess with your readings. This happened to me a lot until I realized what the problem was.
- It can be incredibly unpractical with some fuse types to hold them in your hand and use probes at the same time. Even if you managed to do that, you would need to make sure that your multimeter is facing you, so that you are able to see the reading in time. You can place the fuse on the desk, but who guarantees you that it won’t just roll off due to its small size and lightweight?
- If you are in DIY and you have a clamp designed for holding small objects, this is an excellent time to use it.
- Be extra careful while testing fuses that have burnt out. They shouldn’t break easily, but in cases where the damage was severe, they can break from the faintest touch. If they are made from glass or ceramics, you can cut yourself with ease.
Hopefully, you can now differentiate between several types of fuses and divide them according to their purpose.
If you are not in technical school, you probably won’t try to remember all these things, but I listed them because they can help you a lot while testing fuses.
I believe that you will be able to test fuses a bit faster now and that you will do it in a way that will give you accurate results.