Why are bus bars in indoor switchgear typically plated with silver or tin?

The correct choice emphasizes the role of plating materials like silver or tin in preventing galvanic corrosion when different metals are in contact within the switchgear environment.

In electrical systems, certain metals can undergo galvanic corrosion when they are in contact with dissimilar metals and exposed to an electrolyte, which may happen in humid environments or due to condensation. This corrosion can lead to increased resistance, overheating, and ultimately failure of electrical connections. By applying a layer of silver or tin to bus bars, which often come into contact with other metals, it acts as a protective barrier. This barrier mitigates the potential for corrosion and ensures a more reliable and efficient electrical connection over time.

The other options do not align with the primary goal of using silver or tin plating. While improving the appearance or increasing current capacity may be beneficial in other contexts, the principal reason for such plating in switchgear is to combat the risk of corrosion, ensuring long-term performance and reliability of electrical connections.