Fuse Selection: Don't Confuse These Two Important Concepts

This paper introduces two important concepts of fuse: hot melting value and breaking capacity, as well as their differences and connections.

Does the fuse melting value matter? In short, it's important.

This melting value is to ensure that the heat generated through the fuse during the surge does not have enough time to conduct heat from the fuse to the external circuit. Once the current I and time t are measured, the hot melting value I2t can be easily calculated. When fusing is completed, the fuse produces arc before it is disconnected.

For a fuse, it can have the same rated voltage and current, and the same rated interrupting capacity in the same response time category (slow, medium and fast). However, there are many choices for hot melting value.

Basically, the higher the hot melting value, the longer the fuse will melt, or the more surges the fuse will handle before fusing. This is different from the fuse's breaking capacity, which refers to the maximum current that the fuse can withstand under the specified voltage before breaking the circuit or generating arc. If the glass tube of fuse breaks, the current has exceeded the fuse's breaking capacity. Sometimes things get worse. If the fuse's breaking capacity is not properly selected, the fuse will break or explode. This may cause hazards to the surrounding environment, especially in the presence of combustible gases.

Like most electronic components, temperature and other derating factors should also be taken into account.