Control Devices & PLC Fundamentals is one of 9 topics in the Grade 11 Electrical Technology CAPS syllabus, covered across 3 lessons on Study Vault. Below are real practice questions from this topic with full worked answers.
Sample practice questions
Easy
1. What does overcurrent protection guard a motor against?
Sustained current above the motor's safe rated value, which would cause damaging overheating
Any current flow at all, however small
A supply voltage that is too high, never current
Physical vibration during normal motor operation
Answer: Sustained current above the motor's safe rated value, which would cause damaging overheating — Overcurrent protection guards against sustained current above a motor's safe rated value, which would otherwise cause damaging overheating in the motor windings.
Easy
2. What is the function of the no-volt (zero-volt) coil in a DOL starter?
To prevent the motor from automatically restarting unexpectedly once supply voltage is restored after an outage
To increase the motor's starting torque
To measure the motor's running current continuously
To provide overload protection against sustained excessive current
Answer: To prevent the motor from automatically restarting unexpectedly once supply voltage is restored after an outage — The no-volt coil de-energises if supply voltage drops or fails, dropping out the contactor and stopping the motor, so the start button must be deliberately pressed again once supply is restored, preventing an unattended automatic restart.
Medium
3. Name the DOL starter component that is an electromagnetically operated switch, making and breaking the main power connection to the motor.
Answer: contactor — The contactor is an electromagnetically operated switch that makes and breaks the main power connection to the motor.
