What is a common usage of OR logic?

• A. Two-hand start circuit
• B. An emergency stop pushbutton
• C. The input devices
• D. Remote-start pushbutton

Answer: (D)

OR logic means the output activates if any one of several inputs is true. In control circuits, this lets multiple start signals energize the same output. For starting a machine, having both a local pushbutton and a remote-start pushbutton wired so that either one, when pressed, completes the start circuit is a classic use of OR logic. If either button is pressed, the starter coil energizes and the machine starts.

Two-hand start uses AND logic: both hand switches must be pressed to start, so it’s not OR. An emergency stop pushbutton is designed to break the circuit and stop operation, not to provide an alternative start path, so it doesn’t illustrate OR logic. The input devices option is too general to capture the specific logic relationship. Therefore, a remote-start pushbutton best exemplifies OR logic.