Which metal is used for the guard component in relay assemblies to prevent sticking?

• A. Iron
• B. Aluminum
• C. Copper
• D. Brass

Answer: (D)

The important idea here is choosing a guard surface that stays smooth and separated from the moving parts so the mechanism doesn’t seize or stick as it cycles. Brass fits well because it provides a surface with low friction and good wear resistance, which helps prevent galling and welding to the moving contact surfaces. It’s also non-magnetic, so it won’t disturb the relay’s magnetic circuit, and it resists corrosion, helping maintain a consistent gap over many cycles. In contrast, iron would introduce magnetic attraction that could affect movement, aluminum can wear more quickly and form oxide layers, and copper, while conductive, is more prone to welding under arcing conditions. For these reasons, brass is used for the guard component to keep the relay operation reliable and free of sticking.