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NEC CODE NEC 2020

Motor Circuit Calculations 2 (NEC 430) — NEC 2020 Edition

Free NEC 2020 practice test on motor circuit calculations. Covers branch-circuit and feeder conductor sizing, overload fuse selection, inverse-time breaker sizing, and feeder protection for grouped motors. Simple English, full explanations.

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The National Electrical Code (NFPA 70) is the benchmark standard for safe electrical installation in the US. It is updated every 3 years by the NFPA.

Study the edition adopted by your state. As of 2025, most states use the 2020 or 2023 NEC. These tests are written to the 2023 edition.

The most tested articles are 100 (Definitions), 200–250 (Wiring & Grounding), 300–314 (Wiring Methods), 400–411 (Conductors), 430 (Motors), and 700–701 (Emergency Systems).

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This Motor Circuit Calculations 2 (NEC 430) — NEC 2020 Edition has 30 questions with detailed answers and NEC references. Take the full test, review every wrong answer, and look up the NEC article it references before moving on.

Tip: Use the NEC index (back of the book) — find answers by keyword, not by article number.

Topics covered: NEC articles 100, 210, 220, 240, 250, 300, 310, 430, and special occupancies.
Passing score: Aim for 80%+ on NEC code tests before exam day.
Questions: 30 multiple-choice, one correct answer each

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Motor Circuit Calculations 2 (NEC 430) — NEC 2020 Edition — Question List

Question 1: A 5 HP single-phase motor is connected to a 240-volt supply. What is the minimum size branch-circuit conductor required?

No. 8 THWN
No. 6 THWN
No. 4 THWN
No. 10 THWN

NEC Reference: NEC Table 430.248 / 430.22(A)

Question 2: A 4 HP, 230V single-phase motor has a marked service factor of 1.15 and a nameplate current of 25 A. What standard dual-element fuse size can be used to protect the motor from overload, short circuit, and ground faults?

25 A
30 A
28 A
35 A

NEC Reference: NEC 430.32(A)(1)

Question 3: What size branch-circuit conductor can be used for a 5 HP, 230-volt three-phase motor, with terminals rated at 75 C?

14 AWG
12 AWG
10 AWG
8 AWG

NEC Reference: NEC Table 430.250 / Table 310.16

Question 4: What size inverse-time circuit breaker is required for a 10 HP, 230-volt three-phase motor?

70 A
56 A
40 A
30 A

NEC Reference: NEC Table 430.52 / Table 430.250

Question 5: A feeder supplies two three-phase motors: a 10 HP and a 15 HP, both 230 volts. What is the maximum feeder protection rating allowed?

175 A
105 A
125 A
200 A

NEC Reference: NEC 430.62(A)

Question 6: A feeder supplies a 15 HP and a 10 HP three-phase motor, both 460 volts, with terminals rated at 75 C. What minimum size feeder conductor is required?

8 AWG
6 AWG
10 AWG
12 AWG

NEC Reference: NEC 430.24 / Table 310.16

Question 7: Which of the following motors has the highest full-load current (FLC)?

3 HP, 208 volts three-phase
10 HP, 230 volts three-phase
10 HP, 460 volts three-phase
3 HP, 115 volts single-phase

NEC Reference: NEC Table 430.248 / Table 430.250

Question 8: What size branch-circuit conductor can supply a 3 HP, 115-volt single-phase motor with terminals rated at 60 C?

8 AWG
10 AWG
12 AWG
14 AWG

NEC Reference: NEC Table 430.248 / Table 310.16

Question 9: A 5 HP three-phase motor with a nameplate FLA of 25 A is used for intermittent, 5-minute-rated duty. What size branch-circuit conductor can be used, with terminals rated 75 C?

12 AWG
8 AWG
10 AWG
14 AWG

NEC Reference: NEC Table 430.22(E) / Table 310.16

Question 10: Can the motor branch-circuit short-circuit and ground-fault protective device also fully protect the motor against overload?

True
False -- a separate overload device is needed
Only for single-phase motors
Only for motors under 1 HP

NEC Reference: NEC 430.51

Question 11: Per NEC Table 430.250, what is the full-load current of a 20 HP, 230-volt three-phase motor?

54 amperes
68 amperes
28 amperes
96 amperes

NEC Reference: NEC Table 430.250

Question 12: Per NEC Table 430.52, what is the maximum rating, as a percent of motor FLC, for a non-time-delay fuse (most common motor types)?

300%
175%
250%
125%

NEC Reference: NEC Table 430.52

Question 13: For a feeder supplying a single motor plus other loads (not just motors), how is the feeder protection generally determined?

Motor branch protection plus rating for other loads
Only the motor rating, ignoring other loads
Only the other loads, ignoring the motor
A flat 100 amperes regardless of load

NEC Reference: NEC 430.63

Question 14: Two or more motors, each rated 1 HP or less and drawing not more than 6 amperes, can be grouped on a single branch circuit protected at what maximum standard rating?

20 amperes
15 amperes
30 amperes
40 amperes

NEC Reference: NEC 430.53(A)

Question 15: Per NEC 430.53(B), several motors of any rating can be grouped on one branch circuit if each motor has its own what?

Its own overload protective device
A separate building
A dedicated generator
Nothing extra is required

NEC Reference: NEC 430.53(B)

Question 16: Per NEC Table 430.250, what is the full-load current of a 5 HP, 460-volt three-phase motor?

7.6 amperes
15.2 amperes
28 amperes
3.8 amperes

NEC Reference: NEC Table 430.250

Question 17: When the calculated motor branch-circuit protective device rating does not match a standard size, and the next size down is insufficient, what does NEC 430.52(C)(1) allow?

Using the next higher standard rating
Leaving the motor unprotected
Using a rating with no standard basis
Doubling the calculated value automatically

NEC Reference: NEC 430.52(C)(1)

Question 18: When sizing a feeder that supplies several motors, which single motor's FLC gets the 125% multiplier?

The highest-rated motor
The lowest-rated motor
All motors equally
None of the motors

NEC Reference: NEC 430.24

Question 19: Per NEC Table 430.250, what is the full-load current of a 75 HP, 460-volt three-phase motor?

96 amperes
124 amperes
80 amperes
156 amperes

NEC Reference: NEC Table 430.250

Question 20: When selecting a conductor ampacity from NEC Table 310.16, which temperature column should be used?

The lowest-rated termination temperature
Always the 90 C column
Always the 60 C column
Whichever column gives the smallest wire

NEC Reference: NEC 110.14(C)

Question 21: A motor has a marked service factor of exactly 1.15. Per NEC 430.32(A)(1), what overload percentage applies?

125%
115%
100%
150%

NEC Reference: NEC 430.32(A)(1)

Question 22: When a capacitor is connected on the load side of a motor overload device, what must the motor disconnecting means do?

Disconnect the motor and capacitor together
Disconnect only the capacitor
Disconnect only the motor
Nothing special is required

NEC Reference: NEC 430.113

Question 23: Per NEC Table 430.250, what is the full-load current of a 30 HP, 230-volt three-phase motor?

80 amperes
68 amperes
104 amperes
54 amperes

NEC Reference: NEC Table 430.250

Question 24: Where a motor has a wiring space or terminal housing, what must the space provide for the conductors entering it?

Sufficient space for connections and bending
No space is required
Space only for a padlock
Space only for paint

NEC Reference: NEC 430.12

Question 25: For a motor supplied through an adjustable-speed drive (power conversion equipment), what current value is used for conductor sizing between the drive and the motor?

The drive's rated output current
Only the motor nameplate current
A random estimate
The building service size

NEC Reference: NEC 430.122(A)

Question 26: Per NEC Table 430.250, what is the full-load current of a 1 HP, 230-volt three-phase motor?

3.6 amperes
7.2 amperes
1.8 amperes
14 amperes

NEC Reference: NEC Table 430.250

Question 27: Where must the motor branch-circuit short-circuit and ground-fault protective device generally be located relative to the motor controller?

Ahead of (supply side of) the controller
After the motor windings
Anywhere at all
Inside the motor frame only

NEC Reference: NEC 430.52

Question 28: Per NEC Table 430.250, what is the full-load current of a 30 HP, 460-volt three-phase motor?

40 amperes
80 amperes
20 amperes
65 amperes

NEC Reference: NEC Table 430.250

Question 29: When selecting a thermal overload relay heater element for a motor starter, which current value should generally guide the selection?

The motor nameplate current
The NEC table value only
A random guess
The panel bus rating

NEC Reference: NEC 430.6(A)(2)

Question 30: When Article 430's motor-specific sizing rules conflict with the general conductor and overcurrent rules elsewhere in the NEC, which rules apply?

The specific motor rules in Article 430
The general rules always win
Neither rule applies
Whichever the installer prefers

NEC Reference: NEC 90.3 / Article 430

Key NEC References for This Test

Article	What It Covers
Ch. 1–4	General rules — apply to all installations
Ch. 5–7	Special rules — override Ch. 1–4 where they conflict
Ch. 8	Communications — completely independent of Ch. 1–7
Ch. 9	Tables — referenced by articles, not standalone enforceable rules
Art. 210.12	AFCI — major expansion in NEC 2026
Art. 230.67	Surge protection at service equipment — new NEC 2026

Study Tip: Learn the NEC index — use keywords, not article numbers. Practice finding 5 different topics in under 2 minutes each.

Motor Circuit Calculations 2 (NEC 430) — NEC 2020 Edition

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Motor Circuit Calculations 2 (NEC 430) — NEC 2020 Edition

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Motor Circuit Calculations 2 (NEC 430) — NEC 2020 Edition — Question List

Question 1: A 5 HP single-phase motor is connected to a 240-volt supply. What is the minimum size branch-circuit conductor required?

Question 2: A 4 HP, 230V single-phase motor has a marked service factor of 1.15 and a nameplate current of 25 A. What standard dual-element fuse size can be used to protect the motor from overload, short circuit, and ground faults?

Question 3: What size branch-circuit conductor can be used for a 5 HP, 230-volt three-phase motor, with terminals rated at 75 C?

Question 4: What size inverse-time circuit breaker is required for a 10 HP, 230-volt three-phase motor?

Question 5: A feeder supplies two three-phase motors: a 10 HP and a 15 HP, both 230 volts. What is the maximum feeder protection rating allowed?

Question 6: A feeder supplies a 15 HP and a 10 HP three-phase motor, both 460 volts, with terminals rated at 75 C. What minimum size feeder conductor is required?

Question 7: Which of the following motors has the highest full-load current (FLC)?

Question 8: What size branch-circuit conductor can supply a 3 HP, 115-volt single-phase motor with terminals rated at 60 C?

Question 9: A 5 HP three-phase motor with a nameplate FLA of 25 A is used for intermittent, 5-minute-rated duty. What size branch-circuit conductor can be used, with terminals rated 75 C?

Question 10: Can the motor branch-circuit short-circuit and ground-fault protective device also fully protect the motor against overload?

Question 11: Per NEC Table 430.250, what is the full-load current of a 20 HP, 230-volt three-phase motor?

Question 12: Per NEC Table 430.52, what is the maximum rating, as a percent of motor FLC, for a non-time-delay fuse (most common motor types)?

Question 13: For a feeder supplying a single motor plus other loads (not just motors), how is the feeder protection generally determined?

Question 14: Two or more motors, each rated 1 HP or less and drawing not more than 6 amperes, can be grouped on a single branch circuit protected at what maximum standard rating?

Question 15: Per NEC 430.53(B), several motors of any rating can be grouped on one branch circuit if each motor has its own what?

Question 16: Per NEC Table 430.250, what is the full-load current of a 5 HP, 460-volt three-phase motor?

Question 17: When the calculated motor branch-circuit protective device rating does not match a standard size, and the next size down is insufficient, what does NEC 430.52(C)(1) allow?

Question 18: When sizing a feeder that supplies several motors, which single motor's FLC gets the 125% multiplier?

Question 19: Per NEC Table 430.250, what is the full-load current of a 75 HP, 460-volt three-phase motor?

Question 20: When selecting a conductor ampacity from NEC Table 310.16, which temperature column should be used?

Question 21: A motor has a marked service factor of exactly 1.15. Per NEC 430.32(A)(1), what overload percentage applies?

Question 22: When a capacitor is connected on the load side of a motor overload device, what must the motor disconnecting means do?

Question 23: Per NEC Table 430.250, what is the full-load current of a 30 HP, 230-volt three-phase motor?

Question 24: Where a motor has a wiring space or terminal housing, what must the space provide for the conductors entering it?

Question 25: For a motor supplied through an adjustable-speed drive (power conversion equipment), what current value is used for conductor sizing between the drive and the motor?

Question 26: Per NEC Table 430.250, what is the full-load current of a 1 HP, 230-volt three-phase motor?

Question 27: Where must the motor branch-circuit short-circuit and ground-fault protective device generally be located relative to the motor controller?

Question 28: Per NEC Table 430.250, what is the full-load current of a 30 HP, 460-volt three-phase motor?

Question 29: When selecting a thermal overload relay heater element for a motor starter, which current value should generally guide the selection?

Question 30: When Article 430's motor-specific sizing rules conflict with the general conductor and overcurrent rules elsewhere in the NEC, which rules apply?

Key NEC References for This Test

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