PC Motors and Motor Controls

Question 1

Which NEC article covers motors, motor circuits, and controllers?

Accepted Answer

Article 430

Answer

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

Question 2

What is the minimum ampacity required for branch circuit conductors supplying a single continuous-duty motor?

Accepted Answer

125% of motor FLA

Answer

Per NEC 430.22, branch circuit conductors for a single motor must be sized at no less than 125% of the motor's full-load current.

Question 3

Which device provides both overload protection and short-circuit protection for a motor in a single assembly?

Accepted Answer

Combination motor controller

Answer

A combination motor controller integrates a disconnect means, overcurrent protection, and overload protection in one unit.

Question 4

Per NEC Table 430.52, what is the maximum inverse time circuit breaker rating for a Design B motor with an FLA of 40A?

Accepted Answer

100A

Answer

For Design B motors, NEC Table 430.52 permits up to 250% of FLA for inverse time breakers: 40A × 2.5 = 100A.

Question 5

What is the primary purpose of a motor overload relay?

Accepted Answer

To protect motor windings from damage due to overheating

Answer

Motor overload relays monitor current over time and trip to prevent motor windings from overheating under sustained overload conditions.

(PC) Professional Electrical Contractor Practice Test