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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, 230-volt single-phase motor (Table 430.248) is wired with THWN copper to terminals rated 60 °C. What is the minimum conductor size?

12 AWG
10 AWG
8 AWG
6 AWG

NEC Reference: NEC 430.22 / Table 310.16

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 a 10 HP and a 15 HP motor, both 230-volt three-phase, each protected by inverse-time breakers at 250%. What is the maximum feeder overcurrent device rating?

100 A
125 A
150 A
175 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: A 3 HP, 115-volt single-phase motor is wired with copper conductors to terminals rated 60 °C. What is the minimum branch-circuit conductor size?

10 AWG
8 AWG
6 AWG
4 AWG

NEC Reference: NEC 430.22 / 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: What does a motor branch-circuit short-circuit and ground-fault device sized from Table 430.52 normally NOT provide?

Protection of the branch-circuit conductors against faults
Protection against ground faults
Protection against short circuits
Running overload protection

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: Several motors, each 1 HP or less and drawing 6 A or less, are grouped on a nominal 120-volt branch circuit. What is the maximum branch-circuit protection rating?

20 amperes
15 amperes
30 amperes
40 amperes

NEC Reference: NEC 430.53(A)

Question 15: Motors of any rating may share one branch circuit under 430.53(B) if what condition is met?

The circuit is rated 20 A or less
All motors are the same horsepower
Every motor has a separate disconnect in sight
Each motor has its own overload protection and the branch device suits the smallest motor

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: A 75 HP, 460-volt three-phase motor is supplied by a single branch circuit. What is the minimum conductor ampacity?

125 A
120 A
110 A
96 A

NEC Reference: NEC 430.22

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: A power-factor capacitor is connected on the load side of a motor controller. Is a separate disconnecting means required for the capacitor?

No, it is disconnected with the motor
Yes, always, within sight of the capacitor
Only if the motor is over 50 HP
Yes, unless the capacitor is under 10 kVAR

NEC Reference: NEC 460.8(C)

Question 23: A 30 HP, 230-volt three-phase motor (Table 430.250 FLC 80 A) is protected by time-delay fuses. What is the maximum standard fuse size permitted without the starting exception?

125 A
140 A
150 A
175 A

NEC Reference: NEC 430.52(C)(1)

Question 24: What must a motor terminal housing provide for the field connections?

Sufficient space and enclosure for the conductor connections
Space for a spare motor overload
A window for viewing the windings
A separate disconnect switch

NEC Reference: NEC 430.12

Question 25: How are the conductors between an adjustable-speed drive and its motor sized?

At 100% of the motor nameplate current
At the drive's rated output current
At 125% of the drive rated input current
At least 125% of the motor full-load current

NEC Reference: NEC 430.122(B)

Question 26: A 1 HP, 230-volt three-phase motor is on its own branch circuit. What is the minimum conductor ampacity?

4.2 A
5.25 A
6.0 A
7.2 A

NEC Reference: NEC 430.22

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: A 30 HP, 460-volt three-phase motor (Table 430.250 FLC 40 A) needs a disconnecting means. What is its minimum ampere rating?

40 A
46 A
50 A
60 A

NEC Reference: NEC 430.110(A)

Question 29: Which current is used to size separate motor overload devices (such as starter heater elements)?

The branch-circuit breaker rating
The Table 430.250 full-load current
The conductor ampacity
The motor nameplate current

NEC Reference: NEC 430.6(A)(2)

Question 30: Motor branch-circuit conductors may be protected by a breaker larger than their ampacity. Which rule allows this?

240.4(G), which sends motor circuits to Article 430
240.4(D), the small conductor rule
210.20(A), the continuous-load rule
110.14(C), the termination rule

NEC Reference: NEC 240.4(G)

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 — Question List

Question 1: A 5 HP, 230-volt single-phase motor (Table 430.248) is wired with THWN copper to terminals rated 60 °C. What is the minimum conductor size?

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 a 10 HP and a 15 HP motor, both 230-volt three-phase, each protected by inverse-time breakers at 250%. What is the maximum feeder overcurrent device rating?

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: A 3 HP, 115-volt single-phase motor is wired with copper conductors to terminals rated 60 °C. What is the minimum branch-circuit conductor size?

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: What does a motor branch-circuit short-circuit and ground-fault device sized from Table 430.52 normally NOT provide?

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: Several motors, each 1 HP or less and drawing 6 A or less, are grouped on a nominal 120-volt branch circuit. What is the maximum branch-circuit protection rating?

Question 15: Motors of any rating may share one branch circuit under 430.53(B) if what condition is met?

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: A 75 HP, 460-volt three-phase motor is supplied by a single branch circuit. What is the minimum conductor ampacity?

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: A power-factor capacitor is connected on the load side of a motor controller. Is a separate disconnecting means required for the capacitor?

Question 23: A 30 HP, 230-volt three-phase motor (Table 430.250 FLC 80 A) is protected by time-delay fuses. What is the maximum standard fuse size permitted without the starting exception?

Question 24: What must a motor terminal housing provide for the field connections?

Question 25: How are the conductors between an adjustable-speed drive and its motor sized?

Question 26: A 1 HP, 230-volt three-phase motor is on its own branch circuit. What is the minimum conductor ampacity?

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: A 30 HP, 460-volt three-phase motor (Table 430.250 FLC 40 A) needs a disconnecting means. What is its minimum ampere rating?

Question 29: Which current is used to size separate motor overload devices (such as starter heater elements)?

Question 30: Motor branch-circuit conductors may be protected by a breaker larger than their ampacity. Which rule allows this?

Key NEC References for This Test

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