At the heart of relays, a small component—the electrical contact—plays a crucial role in determining the overall performance and lifespan of the device. Faced with a dazzling array of metals, alloys, sizes, and styles, selecting the most appropriate contact for a specific application has become a science engineers must master. A precise choice ensures long-term, stable system operation Today, we’ll delve deeper into the secrets of electrical contacts used in relays. Selecting relay’s electrical contacts isn’t a simple selection; it’s a systematic decision-making process that requires comprehensive consideration of three key factors:

Rating: It must be perfectly matched to the load characteristics, including switching voltage, current (especially inrush current), and load type (resistive, inductive, lamp load, or motor load).

Style: The shape, size, and construction (e.g., solid contact rivets, bimetal contact rivets tri-metal rivets, powder contact tips, electrical contact assembly) of the contact directly impact its heat dissipation, arc quenching effectiveness, and current-carrying capacity. Neglecting any of these factors can lead to potential failures in demanding applications.

Material: The “gene” of the contact, determining its electrical conductivity, thermal conductivity, hardness, arc resistance, and corrosion resistance. Among numerous electrical contact materials, silver alloys contacts dominate due to their excellent overall performance, making them widely used in general-purpose and power relays for medium- to high-current switching.

AgCdO silver alloy material once dominated the industry for its near-perfect balance of properties. It boasts excellent electrical and thermal conductivity, nearing that of pure silver. Furthermore, its cadmium oxide content imparts unparalleled resistance to arc erosion and welding (sticking), making it an ideal choice for medium- to high voltage connector.

However, its allure harbours hidden dangers: AgCdO contacts is a toxic substance, and its use in contactors and batteries is strictly restricted in many regions of the world. Furthermore, AgCdO contacts processing properties deteriorate as the cadmium oxide content (typically 10-15%) increases. The manufacturing process (pre-oxidation vs. post-oxidation) also directly impacts the uniformity and reliability of material properties.