Journeyman Electrician’s Exam Journeyman Electrician's Motors and Motor Controls 2

Question 1

According to NEC Article 430, the branch-circuit short-circuit and ground-fault protection for a motor must not exceed what percentage of the motor's full-load current for an inverse time breaker?

Accepted Answer

250%

Answer

NEC 430.52 allows inverse time breakers to be sized up to 250% of the motor's full-load current for branch-circuit protection.

Question 2

A motor nameplate reads 'SF 1.15'. What does this service factor indicate?

Accepted Answer

The motor can run at 115% of rated load continuously without damage

Answer

A service factor of 1.15 means the motor can operate at 115% of its nameplate horsepower rating continuously under rated conditions.

Question 3

When sizing conductors for a motor with a 1.15 service factor and 40°C ambient temperature rating, what percentage of full-load current is used?

Accepted Answer

125%

Answer

Per NEC 430.22, motor branch-circuit conductors must have an ampacity of not less than 125% of the motor full-load current.

Question 4

A NEMA MG 1 designation of 'Design B' motor is characterized by:

Accepted Answer

Normal starting torque, normal starting current, and low slip

Answer

NEMA Design B motors have normal starting torque, normal starting current, and low slip at full load — the most common general-purpose motor design.

Question 5

What is the purpose of a motor control center (MCC) compared to individual motor starters?

Accepted Answer

An MCC centralizes multiple motor starters in one enclosure for easier management and wiring

Answer

A motor control center consolidates starters, disconnects, and controls into one assembly, reducing wiring costs and improving maintenance access.

Journeyman Electrician’s Exam Practice Test

Journeyman Electrician’s Exam Practice Test

Journeyman Electrician’s Exam Journeyman Electrician's Motors and Motor Controls 2