Journeyman Electrician Exam (NEC)General Electrical Knowledge and Plan ReadingMedium
A technician is troubleshooting a specific type of AC motor that has brushes and a commutator. This motor is known for its high starting torque and speed control capabilities. Which type of motor is the technician likely working on?
- AUniversal motor
- BSynchronous motor
- CShaded-pole motor
- DSquirrel cage induction motor
Show answer & explanationAnswer & explanation
Correct answer: A. Universal motor
A universal motor is a type of electric motor that can operate on either AC or DC power. It has an armature with windings connected to a commutator and brushes, similar to a DC series motor, giving it high starting torque and variable speed.
Why the other options are wrong
- B. Synchronous motors typically use slip rings for the rotor field, not commutators and brushes for power delivery to the armature.
- C. Shaded-pole motors are a type of single-phase induction motor, known for low starting torque and no brushes/commutator.
- D. Squirrel cage induction motors do not have brushes or commutators; they use electromagnetic induction in the rotor.
Universal Motor Characteristics
A universal motor is a series-wound motor that can operate on both AC and DC power, featuring brushes and a commutator, high starting torque, and variable speed.
- Operates on AC or DC.
- Contains brushes and a commutator.
- High starting torque.
- Speed decreases with increasing load.
Memory trick: Universal motors use brushes and a commutator, so they can power tools and vacuum cleaners with great fervor.