Fuses – everything you need to know

What is a fuse?

A fuse is a simple but very important device that provides protection against current overload or short circuit. It breaks the continuity of a circuit when the current flowing in it exceeds a certain value. Some of the first fuses appeared as early as the end of the 19th century. They performed an important function in primary electrical installations, protecting them from lightning strikes and preventing fires.

The construction and principle of operation of a fuse is very simple. Its key element is a fusible conductor inside, usually a metal wire or tape with an appropriately selected cross-section. The current flowing through the wire causes it to heat up. If the current increases too much, the wire melts and the circuit is interrupted. The fuse can therefore be said to be a kind of “weak point” deliberately placed in the circuit to protect its remaining parts from the effects of surge or overload.

Depending on the application, there are different types, sizes and shapes of fuses to choose from. Often the housing is made of glass or clear plastic – it allows you to easily identify whether the fuse is operational or blown. One of the most common types are glass fuses – in the form of a tube ending in metal contacts on both sides, usually with dimensions of 5x20mm or 6.3x32mm. Other types include blade fuses or ceramic fuses. The latter were once commonly used in home electrical installations. Today, however, they have been mostly replaced by modern circuit breakers.

How to choose the right fuse for my device?

In order for a fuse to effectively protect a device, its parameters must be properly selected. The most important of them is rated current – it is the value of current, after exceeding which the fuse cuts off the current flow. In order to choose an appropriate fuse for your device, its maximum current draw should be within the range of fuse rated current with some margin.

Equally important is the delay characteristics of the fuse. It determines how fast the fuse will blow when the current rating is exceeded. There are time-delay (slow-blow), medium-delay, fast and super-fast blow fuses. The speed of reaction is also dependent on the magnitude of overcurrent – the more the rating is exceeded, the faster the fuse blows. In some cases, when the current rating is exceeded only slightly, the time to cut off may reach several minutes. More information about the fuse timing, such as the graph of fuse activation time on the current, can be found in the data sheet.

When a fusible link burns out, an electric arc is produced. The arc can continue to conduct the current, additionally increasing the cutoff delay. For this reason, the breaking capacity of a fuse must also be considered. It determines the maximum current that the fuse can safely disconnect, without the electric arc lasting too long or other unexpected events occurring – such as the destruction of the fuse. Breaking capacity is usually many times higher than the rated current, typically in the range of tens to thousands of amperes. Some types of fuses, especially those rated for higher voltages, are designed to dissipate the arc as quickly as possible. Examples of such fuses include the ones filled with powder (quartz sand) or liquid.

Don’t forget that fuses are single-use devices. Once the fuse has served its purpose, it must be replaced with a new one. For this reason, it is recommended to use fuse sockets, which allow the fuse to be securely fixed in the device, as well as quickly replaced. Our company, InterElcom, is proud to offer the highest quality fuse sockets, with PCB, wire or device housing mounting. You can find a large selection of them in our product catalogue. We also encourage you to check out our offer of glass fuses and polymer fuses, as well as to ask any questions via the contact form on our website.

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