How To Identify a Fuse on a Circuit Board? (Types & Features)

How To Identify a Fuse on a Circuit Board? (Types & Features) |

Fuses are the safety barriers in any electric or electronic circuit, and they protect the circuits against any power surge or unexpected high currents. However, when the fuses are blown or tripped, they might need to be replaced, so how to identify a fuse on a circuit board?

How To Identify a Fuse on a Circuit Board?

You should look for the part number and the manufacturer’s name which are enough to identify the fuse, if you are replacing a fuse, you should be able to identify the fuse in the circuit correctly. Unfortunately, the fuse could be missing this information, so you would have to examine the fuse more to identify it.

 When you start examining the part, you should start with the metal cap, as it might have some marking stamped on it. These markings could be important information about the fuse model, type, or manufacturer.

What Are the Part Number & the Manufacturer of a Fuse?

Fuses can have many different manufacturers, and each fuse could belong to a certain brand manufacturer. The most important information on a fuse that would ease identifying it is the part number; however, you might not find a part number on the fuse.

 If you didn’t find the part number of the fuse, you would need to use other identifications methods. The part number of the fuse would usually have the ampere rating of the fuse. So, you can use the part number to know the fuse’s ampere rating without measuring them.

What Does Ampere Rating Mean?

It’s the amount the fuse could carry in normal conditions, the fuse ampere rating is shown in the part number of the fuse, and usually in amperes, for example, 0.5A or 10A, but it can also be shown in milliamperes 50 mA. This is because some people confuse the fuse ampere rating and the fuse interrupting rating.

Interrupting Rating

It’s the maximum amount of current the fuse will be able to interrupt safely at rated voltage. Interrupting rating can also be called a short circuit or breaking circuit rating. When the fuse receives an expected high current, this only happens when the circuit is experiencing short circuits.

The fuse should stay intact for safety purposes, where there are no ruptures in the body or explosions, and the circuit is clear.

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What Is the Voltage Rating of a Fuse?

The voltage rating of a fuse is usually expressed on the fuse in volts; the fuses can be either used for alternating current voltages “ACV” such as 250 ACV or be used for direct current “DCV” such as 32 DCV. Fuses should only be used in circuits that meet their voltage specifications.

DC fuses should be installed only in DC circuits; meanwhile, AC fuses should be installed only in AC circuits. On the contrary, you might find some fuses used for both AC and DC circuits, but they are designed to do so, for example, 450DC/600AC. In addition, fuses can have symbols on them to identify whether they are DC or AC.

The AC symbol has the shape of a wave, which represents the alternating current because it changes its direction with time during regular intervals. The DC symbol has the shape of two lines above each other, one of the lines is solid, and the other is dashed.

What Does Fuse’s Element Speed Mean?

The fuse must open at any short circuit or unexpected high current; the speed that takes the fuse to be opened is the element speed. Three main factors control the Fuse’s element speed:

  1. Overload Current
  2. Material of The Fuse Element
  3. Operating Temperature

The markings found on the fuse differ according to the fuse’s size; for example, large fuses use the markings gM or gL; meanwhile, the small fuses use the markings M or L. In addition, the fuses can be described in many descriptions such as fast-acting, slow-acting, motor rated, etc. If your fuse doesn’t have markings for element speed.

Then, you would need to have a datasheet and the manufacturer’s part number to determine the fuse’s speed.


What Are The Fuse’s Dimensions?

When identifying a fuse, you have to be very accurate when measuring the dimensions because many fuses are similar in dimensions. For example:

  • The Cartridge Fuses
    Measure the caps’ diameter and the overall fuse’s length.
  • The Bottle Fuses
    The caps’ size usually differs, so you should measure their fuse’s diameter and the fuse length.
  • The Blade Fuses
    They have multiple measurements:
    • The overall fuse’s length “D.”
    • The fuse’s body length and diameter “A&B.”
    • The fixing center “G.”
    • The size of the fixing hole “H.”
    • The blade/tag thickness and width “E&F.”

What Are The Features of Each Fuse?

The features of a fuse are the points used to separate it from other fuses and make it easier to distinguish it from others; for example, the material of the fuse body can be made of ceramic, glass, or plastic. In addition, the fuse trip indication type can either be a trip or a blown fuse, and The fuse could also have a microswitch fitter.

The last feature to distinguish a fuse is the fuse’s body style, for example:

  • SMD “surface mount device” or PCB “printed circuit board” device.
  • Cartridge Fuse or Bottle Fuse.
  • Metal/Blade Fuse.

What Are The Types of Fuses?

The main two types of fuses are the DC and the AC fuses; they differ according to the current type, whether it’s alternating current or direct current. The fuse used for DC can’t be used for AC, and vice versa; however, some fuses are used for both types.

The DC Fuse

The DC fuses generate a harder arc than the arc produced in the AC circuits because the DC has no zero flows. To reduce the size of the arc effect, the fuse sizer should be increased. Therefore, the electrodes are located far from the fuse, so the fuse size is larger.

The AC Fuse

The AC circuits’ arc is easier to extinguish because the alternating current moves in the form of waves changing its amplitude during regular intervals. Therefore, the AC can go from 60 to 0 and vice versa; the AC fuses are divided into two types which are high voltages and low voltage fuses.


What Are The Applications of Fuses?

Fuses have many types, whether electrical or electronic, and they can be used in many applications and devices, electrical and electronic, for example:

  • The main protection barrier for many applications and devices such as motors, transformers, and power systems. The fuse is used to protect them from any unexpected high currents.
  • Used in solar circuits, power transformers, and feeders.
  • For domestic purposes related to distribution boards in houses and electrical appliances.
  • Fuses can be found in many other devices such as hard disk drivers, laptops, scanners/printers, and electronic devices.
  • Fuses also have an essential role in smartphones and gaming systems.


To sum up, the part number and manufacturer’s name are the first step in identifying a fuse. When replacing a fuse, you should be very precise when identifying the fuse type because there are many types of fuses. The metal cap of the fuse is the first place to start looking at as it usually has the markings of the fuse.

Each fuse has markings stamped on it, and they could contain the part number, the manufacturer’s name, the ampere ratings, and the voltage ratings. The ampere rating could also be found in the part number, either amperes or milliamperes. The voltage markings can differ due to the size of the fuse.

There are many other features that you can use to distinguish the fuse; for example, the material of the fuse body can be made of ceramic, glass, or plastic. The fuse trip indication type can either be a trip or a blown fuse, and the fuse could also have a microswitch fitter. In addition to its body style:

  • SMD “surface mount device” or PCB “printed circuit board” device.
  • Cartridge Fuse or Bottle Fuse.
  • Metal/Blade Fuse.

Fuses are very important and are used in many applications such as laptops, hard disk drivers, scanners/printers, smartphones, and electronic devices.

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