True or False: A two-wire control for a motor will restart automatically when power is restored after a power failure.

True or False: A two-wire control for a motor will restart automatically when power is restored after a power failure.

• A. True
• B. False
• C. Not Specified
• D. Depends on the system

Answer: (A)

In a simple two-wire motor control, the control circuit is fed directly from the line and uses a normally closed stop contact, a normally open start pushbutton, and a holding contact to latch the coil. When power is restored after a outage, line voltage again reaches the control circuit. With the stop contact in its normally closed state and the latch path intact, the coil can energize again and pull in the contactor, which starts the motor automatically. The start button is only needed to initiate operation when power is already on; after a restart, the latch keeps the circuit energized. Of course, if someone has pressed the stop button to open the circuit or if the system is wired to prevent auto-restart, it wouldn’t restart automatically. But in the typical basic two-wire setup, automatic restart on power restoration is expected.

In a simple two-wire motor control, the control circuit is fed directly from the line and uses a normally closed stop contact, a normally open start pushbutton, and a holding contact to latch the coil. When power is restored after a outage, line voltage again reaches the control circuit. With the stop contact in its normally closed state and the latch path intact, the coil can energize again and pull in the contactor, which starts the motor automatically. The start button is only needed to initiate operation when power is already on; after a restart, the latch keeps the circuit energized.

Of course, if someone has pressed the stop button to open the circuit or if the system is wired to prevent auto-restart, it wouldn’t restart automatically. But in the typical basic two-wire setup, automatic restart on power restoration is expected.