Fuse

Figure 66 shows the schematic symbol for the fuse. Fuses are used to protect the circuit from over current conditions. The fuse is installed in the circuit so that all the current in the circuit passes through it. In most fuses, the strip of metal is made of an alloy of tin and bismuth, which will melt and open the circuit when the current exceeds the rated capacity of the fuse. For example, if a 5-amp fuse is placed into a circuit, the fuse will allow currents up to 5 amps to pass. Because the fuse is intended to protect the circuit, it is quite important that its capacity match the needs of the circuit in which it is used.

When replacing a fuse, consult the applicable manufacturer’s instructions to be sure a fuse of the correct type and capacity is installed. Fuses are installed in two types of fuse holders. “Plug-in holders” or inline holders are used for small and low capacity fuses. “Clip” type holders are used for heavy high capacity fuses and current limiters.