A technician is installing a control circuit for a 3-phase compressor motor. The circuit requires a start/stop station and an emergency stop button. The emergency stop (E-stop) button must de-energize the motor starter regardless of the state of the start/stop buttons. Where should the E-stop button typically be wired in a conventional 3-wire control circuit?

Question: A technician is installing a control circuit for a 3-phase compressor motor. The circuit requires a start/stop station and an emergency stop button. The emergency stop (E-stop) button must de-energize the motor starter regardless of the state of the start/stop buttons. Where should the E-stop button typically be wired in a conventional 3-wire control circuit?

Answer options:

• In parallel with the start button
• In series with the motor starter coil, after the overload contacts ✅ In series with the stop button, before the start button and seal-in branch
• Across the main power supply to the motor

Correct answer: In series with the stop button, before the start button and seal-in branch

Explanation: For an E-stop to provide an absolute stop function, it must interrupt the control circuit power to the motor starter coil by being wired in series with the stop button, thus breaking the circuit regardless of the start button being pressed or the seal-in contact being closed. Wiring it otherwise would not guarantee a complete and immediate shutdown of the control circuit to the coil.