The material used for making fuse wire must have properties such as low melting point, low ohmic loss, and high conductivity. Fuse wire is generally made of materials like tin, lead, or zinc with low melting points.
A metal with high specific resistance and low melting point is shown in the table below.
| Metal | Melting Point in Celsius | Specific Resistance | Value of Fuse constant k for d in mm |
|---|---|---|---|
| Silver | 980 | 16 | – |
| Tin | 240 | 112 | 12.8 |
| Zinc | 419 | 60 | – |
| Lead | 328 | 210 | 10.8 |
| Copper | 1090 | 17 | 80 |
| Aluminium | 665 | 28 | 59 |
Fuse elements are typically made of materials such as tin, lead, silver, copper, zinc, aluminum, and an alloy of lead and tin. However, for small current rating fuses, an alloy of lead and tin is preferred. However, this alloy is not suitable for currents exceeding 15A as the wire diameter will be larger, and the amount of metal released after fusing will be excessive.
When circuits exceed a 15A rating, copper wire fuses are used. However, using copper wire as a fuse material has some drawbacks. For instance, if a low fusing factor is desired, the wire operates at a high temperature. This can cause overheating, leading to a reduction in the wire’s cross-sectional area and fusing current. In extreme cases, the wire may melt prematurely.
Silver is utilized as a fuse material due to its numerous advantages, which include:
- It does not oxidize.
- The conductivity does not deteriorate with oxidation.
- Owing to its high conductivity, the amount of molten metal handled is minimized, making the operating speed fast.
However, silver is an expensive metal, so usually materials such as copper or an alloy of lead and tin are used as fuse wires instead. Zinc in the form of a strip is also used as a fuse element because it can handle a small overload without melting quickly.