In a three wire control circuit, when a power failure occurs, which statement is true?

In a three wire control circuit, when a power failure occurs, which statement is true?

• A. The interlock contact will close the circuit.
• B. The operator can restart the meter automatically.
• C. The motor can restart unexpectedly.
• D. The operator must restart the meter manually

Answer: (D)

In a three-wire control circuit, there is a start/stop arrangement with a holding contact that keeps the coil energized after you release the start button. When power fails, the entire control circuit loses voltage, the coil de-energizes, and the holding contact opens, so the load (like a meter or motor) stops. After power is restored, there’s no automatic re-energizing of the control because the latch is broken; the operator must press the start control again to energize the circuit and restart. This is why the correct statement is that the operator must restart the meter manually. The other options aren’t right because there isn’t an automatic closing of an interlock on power return, nor automatic auto-restart of the load, nor an automatic restart without operator action.

In a three-wire control circuit, there is a start/stop arrangement with a holding contact that keeps the coil energized after you release the start button. When power fails, the entire control circuit loses voltage, the coil de-energizes, and the holding contact opens, so the load (like a meter or motor) stops. After power is restored, there’s no automatic re-energizing of the control because the latch is broken; the operator must press the start control again to energize the circuit and restart. This is why the correct statement is that the operator must restart the meter manually. The other options aren’t right because there isn’t an automatic closing of an interlock on power return, nor automatic auto-restart of the load, nor an automatic restart without operator action.