CEA CEA Motor Controls and Control Circuits Questions and Answers 2

Question 1

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

Accepted Answer

Mechanical and/or electrical interlocking

Answer

A time-delay relay

Answer

A phase monitor relay

Answer

A selector switch only

Question 2

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

Accepted Answer

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

Answer

It closes its contacts instantly when energized, then opens them after a set time

Answer

It opens its contacts instantly when de-energized

Answer

It delays turning off the coil

Question 3

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

Accepted Answer

Limit switch

Answer

Overload relay

Answer

Phase failure relay

Answer

Control transformer

Question 4

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

Accepted Answer

120V

Answer

480V

Answer

208V

Answer

24V DC

Question 5

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

Accepted Answer

Maintained-contact device such as a toggle switch or thermostat

Answer

Momentary-contact pushbutton

Answer

Selector switch with spring return

Answer

Emergency stop button only

Question 6

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

Accepted Answer

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

Answer

To balance loads across circuits

Answer

To convert three-phase power to single-phase

Answer

To reduce starting current