When working with relays, understanding relay contact layouts is essential for designing reliable electrical circuits. The three primary relay contact types are normally open (NO), normally closed (NC), and SPDT, each serving a distinct role. Picking the correct contact depends on the desired behavior when activated.

A normally open (NO) contact is in an open state when the relay is de-energized, meaning current cannot pass. When the relay activates, the contact closes, allowing current to flow. This setup is well-suited for use cases where a device should turn on only when triggered, such as energizing a solenoid via an external trigger.

A NC contact operates in the opposite manner. It is closed by default when the relay is de-energized, permitting continuous current flow. When power is applied to the coil, the contact opens, interrupting the circuit. This configuration is ideal for fail-safe applications, where operation continues until triggered to stop, such as an emergency stop button.

Changeover contacts merge two contact states into one switching unit. They feature a switching point that alternates between two fixed contacts. When not powered, the common terminal is connected to the closed path. When on, it switches to the NO contact. This makes changeover relays perfect for applications requiring alternating between two circuits, such as redirecting energy to a generator.

Assessing your circuit requirements—whether you need to engage a load, turn it off, or change circuit routing—will help you choose the right relay. Always verify the relay’s manufacturer documentation to confirm the contact configuration and verify load capacity, guaranteeing proper functionality. Choosing the right relay configuration not only ensures proper functionality but also reduces failure risk.