CEA Motor Controls and Control Circuits Questions and Answers Flashcards

In a wye-delta reduced-voltage starter, what is the motor connection at startup?

Answer: Wye (star)

During startup the motor is connected in wye, which applies approximately 58% of line voltage to each winding, reducing inrush current to about one-third.

What NEC article primarily covers the installation of motor circuits and controllers?

Answer: Article 430

NEC Article 430 covers motors, motor circuits, and controllers, including conductor sizing, overcurrent protection, and disconnecting means requirements.

According to the NEC, the branch-circuit short-circuit and ground-fault protective device for a motor is permitted to be sized larger than the conductor ampacity. What is the maximum percentage of full-load current allowed for an inverse-time breaker protecting a Design B motor?

Answer: 250%

NEC Table 430.52 allows an inverse-time circuit breaker for a Design B squirrel-cage motor to be sized up to 250% of the motor's full-load current.

What is the minimum disconnect switch ampere rating required for a motor branch circuit?

Answer: 125% of the motor full-load current

Per NEC 430.110, the motor disconnecting means must have an ampere rating of at least 115% of the motor's full-load current.

Which type of motor control device uses a bimetallic strip or melting alloy (solder pot) to sense motor overload?

Answer: Thermal overload relay

Thermal overload relays use a bimetallic strip or melting alloy element that responds to heat generated by excess current flowing through it.

When sizing overload relay heaters for a motor with a service factor of 1.15, the overload device must not exceed what percentage of the motor's full-load current?

Answer: 125%

Per NEC 430.32(A)(1), for motors with a marked service factor of 1.15 or greater, the overload device must not exceed 125% of the motor's full-load current.