In relay logic, what function does a seal-in circuit perform?

• A. It provides a time delay before de-energizing
• B. It translates control signals into binary data
• C. It provides memory to keep the relay energized after the control input is removed
• D. It isolates the control circuit from the load

Answer: (C)

A seal-in circuit creates memory in relay logic by using the relay’s own contact to hold the coil energized after the control input is released. When the control input is activated, the relay energizes and its normally open contact closes, forming a holding path that bypasses the control switch. This keeps the coil energized even after the control input goes away, until a stop command or power loss opens the circuit. This is why it’s described as a memory or self-holding function. It isn’t about delaying de-energization, translating signals into binary data, or isolating control from load—the seal-in’s purpose is to latch the relay on so it remains energized.