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BASIC NEC 2023

Motor Nameplate Data, Horsepower & Torque Basics Practice Test

Free online motor nameplate and horsepower/torque practice test. 25 basic electrical questions on reading motor nameplates, synchronous speed, slip, and torque calculations. Good for electrician exam prep.

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Nameplate Basics Synchronous Speed Motor Slip HP and Watts Torque Basics Torque and HP

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A motor's nameplate is packed with information every electrician needs to read correctly: horsepower, voltage, full-load amps (FLA), RPM, service factor, and more. Understanding synchronous speed (the theoretical maximum speed based on frequency and pole count) and slip (how much slower the motor actually runs) explains why induction motors never quite reach their synchronous speed. Connecting horsepower, torque, and RPM together lets you evaluate whether a motor can actually do the mechanical job required of it.

25

Questions

38 min

Time

75%

Pass

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Motor Nameplate Data, Horsepower & Torque Basics Practice Test — Question List

Question 1: Which of the following is typically printed on a standard motor nameplate?

Horsepower, voltage, full-load amps, and RPM
Only the manufacturer's logo, with no technical data
The installer's name and phone number
The building's street address

Question 2: "Full-load amps" (FLA) on a motor nameplate refers to:

The current the motor draws when delivering its full rated horsepower output
The maximum current the motor could ever draw under any fault condition
The current drawn with the motor completely disconnected
The voltage rating of the motor

Question 3: A motor with a service factor (SF) of 1.15 means:

The motor can handle up to 15% overload above its rated horsepower continuously without immediate damage
The motor will fail immediately if run at its rated horsepower
The motor requires 15% less voltage than rated
Service factor has nothing to do with load capacity

Question 4: The formula for calculating an AC induction motor's synchronous speed is:

RPM = 120 x f / poles
RPM = poles / f
RPM = f x poles
RPM = 60 / f

Question 5: What is the synchronous speed of a 4-pole motor operating on a 60 Hz supply?

900 RPM
1,800 RPM
3,600 RPM
7,200 RPM

Question 6: What is the synchronous speed of a 2-pole motor operating on a 60 Hz supply?

1,800 RPM
2,400 RPM
3,600 RPM
7,200 RPM

Question 7: What is the synchronous speed of a 6-pole motor operating on a 60 Hz supply?

900 RPM
1,200 RPM
1,800 RPM
3,600 RPM

Question 8: "Slip" in an induction motor refers to:

The difference between synchronous speed and the motor's actual running speed
The voltage drop across the motor's terminals
A defect found only in damaged motors
The motor's horsepower rating

Question 9: Why does a standard induction motor always run at a speed slightly SLOWER than its synchronous speed?

The rotor needs relative motion (slip) compared to the rotating magnetic field to have current induced into it, which is what produces torque
Induction motors are simply built incorrectly by design
There is no real reason, it is completely random
Synchronous speed is always lower than actual running speed

Question 10: One horsepower (HP) equals how many watts?

746 W
550 W
1,000 W
100 W

Question 11: A motor is rated at 5 HP. Approximately how many watts of mechanical power output is that?

746 W
2,500 W
3,730 W
5,000 W

Question 12: "Torque," in the context of a motor, is best described as:

A rotational (twisting) force, commonly measured in pound-feet (lb-ft) or newton-meters (N-m)
A unit of electrical resistance
The motor's voltage rating
The motor's physical weight

Question 13: The formula relating horsepower, torque, and RPM is:

HP = Torque x RPM / 5252
HP = Torque / RPM
HP = Torque + RPM
HP = 5252 / (Torque x RPM)

Question 14: A motor produces 10 lb-ft of torque at 1,750 RPM. Approximately how much horsepower is that?

1.75 HP
3.33 HP
10 HP
17.5 HP

Question 15: For a FIXED horsepower rating, if a motor's RPM is increased, what happens to its torque?

Torque decreases
Torque increases
Torque stays exactly the same
Torque becomes zero

Question 16: A NEMA frame number/designation on a motor nameplate primarily relates to:

The motor's standardized physical mounting dimensions (shaft height, bolt pattern, shaft diameter, etc.)
The motor's exact electrical horsepower rating
The motor's color scheme
The manufacturer's warranty period

Question 17: A motor marked for "continuous duty" versus one marked for "intermittent duty" differs in that:

A continuous-duty motor is rated to run indefinitely at its full load, while an intermittent-duty motor is only rated for short bursts followed by rest/cooling periods
They are exactly the same rating with a different name
Intermittent duty means the motor can never be turned off
Continuous duty means the motor runs only in reverse

Question 18: A motor's efficiency, expressed as a percentage, represents:

The ratio of useful mechanical power output to the total electrical power input
The motor's exact RPM rating
The motor's voltage rating only
The number of poles in the motor

Question 19: A 4-pole, 60 Hz motor has a synchronous speed of 1,800 RPM but its nameplate shows an actual full-load speed of 1,750 RPM. What is the slip, in RPM?

20 RPM
50 RPM
1,750 RPM
1,800 RPM

Question 20: Using the 50 RPM slip from the previous example (synchronous speed 1,800 RPM), what is the percent slip?

0.28%
2.8%
28%
50%

Question 21: "Locked rotor amps" (LRA), sometimes shown on a motor nameplate, refers to:

The very high current the motor draws for a brief moment at the instant of starting, before it begins to spin up
The current drawn only after the motor has been running for 24 hours straight
The motor's voltage rating
A rating that never applies to induction motors

Question 22: A motor outputs 2,238 watts of mechanical power. Approximately how many horsepower is that?

1 HP
2 HP
3 HP
6 HP

Question 23: Some motor nameplates list two voltages, such as "208-230/460 V." This dual voltage rating means:

The motor windings can be internally reconfigured (typically via connection changes) to operate correctly on either of the listed voltage systems
The motor runs both voltages simultaneously at all times
It is a typo and only one voltage is ever valid
The motor requires both voltages to be applied at once

Question 24: What is the synchronous speed of an 8-pole motor operating on a 60 Hz supply?

450 RPM
900 RPM
1,800 RPM
3,600 RPM

Question 25: For a fixed 60 Hz supply frequency, as a motor's number of poles INCREASES, its synchronous speed:

Decreases
Increases
Stays exactly the same
Becomes zero immediately

EXAM CARD BASIC

Questions25

Time limit38 min

Pass score75%

Code editionNEC 2023

DifficultyIntermediate

Last reviewedJun 2026

Timer starts immediately. Progress is auto-saved.

Source: NEC 2026 (NFPA 70)