Journeyman Electrician's Motors and Motor Controls Flashcards
7 cards from real Journeyman Electrician’s Exam practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Journeyman Electrician's Motors and Motor Controls flashcards as text
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?
Answer: 250%
NEC 430.52 allows inverse time breakers to be sized up to 250% of the motor's full-load current for branch-circuit protection.
A motor nameplate reads 'SF 1.15'. What does this service factor indicate?
Answer: The motor can run at 115% of rated load continuously without damage
A service factor of 1.15 means the motor can operate at 115% of its nameplate horsepower rating continuously under rated conditions.
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?
Answer: 125%
Per NEC 430.22, motor branch-circuit conductors must have an ampacity of not less than 125% of the motor full-load current.
A NEMA MG 1 designation of 'Design B' motor is characterized by:
Answer: Normal starting torque, normal starting current, and low slip
NEMA Design B motors have normal starting torque, normal starting current, and low slip at full load — the most common general-purpose motor design.
What is the purpose of a motor control center (MCC) compared to individual motor starters?
Answer: An MCC centralizes multiple motor starters in one enclosure for easier management and wiring
A motor control center consolidates starters, disconnects, and controls into one assembly, reducing wiring costs and improving maintenance access.
A 3-phase motor is connected in a wye (Y) configuration. If the line voltage is 480V, what is the voltage across each motor winding?
Answer: 277V
In a wye connection, phase voltage equals line voltage divided by √3, so 480V ÷ 1.732 ≈ 277V per winding.
Under NEC 430.109, which device is NOT acceptable as a motor disconnecting means?
Answer: A standard lighting switch rated 15A
A standard lighting switch is not rated for motor loads and is not listed as an acceptable disconnecting means under NEC 430.109.