What term describes a method of maintaining current flow after a momentary switch has been pressed and released?

• A. Seal-in circuit
• B. Interlox
• C. Latch
• D. Transducer

Answer: (A)

This item tests how to keep power to a circuit after a momentary pushbutton is released. The method used is a seal-in circuit.

When you press the momentary switch, the control coil energizes. A contact that belongs to the same coil is wired in parallel with that pushbutton, so once the coil pulls in, this holding contact closes and provides a path to keep the coil energized even after the pushbutton is released. That self-holding path is what creates the seal-in, or holding, circuit.

Interlox isn’t about maintaining power in a control circuit, and a transducer is a device that converts energy from one form to another. A latch can describe a memory/holding behavior, but in PLC practice the specific mechanism described here is called a seal-in circuit.