What primarily causes a fuse link to melt or blow?

The primary cause of a fuse link melting or blowing is excessive current flowing through it, which directly relates to the resistance in the fuse. When current passes through the fuse, the inherent resistance generates heat due to electrical energy being converted to thermal energy. If the current exceeds the fuse's rated capacity, the heat produced can rise to a level where the material of the fuse link cannot withstand it, leading to the melting of the metal strip or element within the fuse. This is a critical safety mechanism to prevent further damage to the electrical system and to protect against potential hazards like overheating or electrical fires.

While other factors like excessive voltage might overload a circuit, it is the current, primarily influenced by the resistance, that ultimately causes the fuse to react and protect the circuit. External heat sources and incorrect installation may contribute to problems in an electrical system, but are not the primary reasons for a fuse link melting or blowing. Understanding the relationship between current, resistance, and the operation of fuses is essential for effectively designing and maintaining safe electrical systems.