CEA Motor Controls and Control Circuits Questions and Answers Flashcards

In a forward/reverse motor control circuit, what must be used to prevent both forward and reverse contactors from energizing simultaneously?

Answer: Mechanical and/or electrical interlocking

Interlocking (both mechanical between the contactor frames and electrical using normally closed auxiliary contacts) prevents both contactors from closing at the same time, which would cause a short circuit.

What does a time-delay relay (TDR) set for 'on-delay' do?

Answer: It waits a preset time after being energized before changing contact states

An on-delay TDR energizes its coil immediately but waits the set time interval before its timed contacts change state.

Which device in a motor control circuit is used to stop the motor automatically when a conveyor reaches a certain position?

Answer: Limit switch

A limit switch is a mechanical position sensor wired into the control circuit that automatically opens or closes contacts based on physical position.

What is the typical control circuit voltage supplied by a control transformer in a magnetic starter panel?

Answer: 120V

Most industrial motor control circuits use a control transformer to step the line voltage down to 120V for safer and more standardized control wiring.

A two-wire control circuit uses which type of pilot device?

Answer: Maintained-contact device such as a toggle switch or thermostat

Two-wire control uses a maintained-contact device that holds the circuit open or closed without operator presence, providing low-voltage release and automatic restart.

What is the purpose of a phase monitor relay in a three-phase motor installation?

Answer: To protect the motor by tripping if a phase is lost or severely unbalanced

A phase monitor relay detects phase loss, phase reversal, or severe voltage imbalance and opens the control circuit to prevent motor damage.