Motors and Transformers Practice Test

The maximum rating of overcurrent protection for transformers rated 1000 volts, nominal, or less is typically determined using:

• ATable 450.3(B)
• BTable 310.16
• CTable 430.52
• DTable 240.6

In NEC motor terminology, a 'controller' is MOST closely associated with:

• AStarting and stopping the motor and regulating its operation
• BProviding the grounding electrode connection
• CSizing the branch-circuit conductor ampacity
• DDetermining conduit fill percentage

A motor branch-circuit conductor sizing question asks for the minimum conductor ampacity. The FIRST step is to determine:

• AThe motor full-load current (FLC) per Article 430 (table or nameplate as required)
• BThe box fill volume
• CThe conduit fill percentage
• DThe grounding electrode system resistance

A NEMA code letter on a motor nameplate MOST closely relates to:

• ALocked-rotor current/starting kVA characteristics
• BMotor insulation temperature rating
• CConduit fill allowance
• DEquipment grounding conductor size

Transformer secondary conductors not over 25 ft long may be installed without secondary overcurrent protection at the transformer if they comply with:

• A240.21(C)(6)
• B450.3
• C430.52
• D310.16

A motor's controller disconnect is 30 ft from the motor and is visible from both the motor and the driven machinery. Is a separate motor disconnect required?

• ANo; the controller disconnect can also serve as the motor disconnect because it is within sight from the motor and driven machinery
• BYes; a separate motor disconnect is always required
• CYes, unless the controller disconnect is lockable
• DNo, because the motor has overload protection

A motor branch circuit is being designed. Which statement BEST describes the NEC roles of the key protection/sizing items (typical exam concept)?

• AConductors are sized by motor rules (often 125% FLC); the branch-circuit OCPD is sized for short-circuit/ground-fault protection and motor starting; overload protection protects the motor from overheating
• BThe branch-circuit breaker is the overload protection for the motor, so separate overloads are not needed
• CThe equipment grounding conductor carries normal return current, so it protects the motor from overload
• DBonding the neutral and ground in the controller prevents nuisance tripping and is required

A motor has a Table FLC of 28A. What is 125% of this current (common motor calculation step)?

• A35 A
• B32 A
• C28 A
• D42 A

For a single grounded separately derived system, the grounding electrode conductor is sized in accordance with:

• A250.66
• B450.3
• C310.16
• D430.52

Which NEC article is the primary location for motor controllers and disconnecting means requirements?

• AArticle 430
• BArticle 240
• CArticle 250
• DArticle 110

A single hermetic refrigerant motor-compressor has a rated-load current of 20A (larger than its branch-circuit selection current). What is the minimum ampacity of its branch-circuit conductors?

• A20A
• B25A
• C35A
• D45A

A motor nameplate is marked 10 HP, 208-230/460 Volts, and 30.8-28/14 Amps. Connected to a 460-volt circuit, what nameplate current is the starting point for sizing separate overload protection?

• A30.8 A
• B28 A
• C14 A
• D10 A

Transformer overcurrent protection requirements are primarily found in:

• A450.3
• B430.52
• C240.6
• D310.16

Class 2 thermostat conductors are to be pulled into the same raceway as 120-volt branch-circuit power conductors, with no barrier. This is generally:

• APermitted if the Class 2 conductors are 18 AWG
• BNot permitted; Class 2 conductors must be separated from power conductors
• CPermitted if the raceway is metal
• DPermitted if the power circuit is 15A

A single continuous-duty motor has a table FLC of 28 amps. What is the calculated minimum branch-circuit conductor ampacity?

• A35 A
• B28 A
• C56 A
• D30 A