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NEC CODE NEC 2020

Motor Circuit Calculations 3 (NEC 430/440) — NEC 2020 Edition

Free NEC 2020 practice test on motor and motor-compressor circuit calculations. Covers hermetic refrigerant motor-compressor branch-circuit and short-circuit protection (Article 440), controllers, and disconnecting means (Article 430). 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 3 (NEC 430/440) — 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 3 (NEC 430/440) — NEC 2020 Edition — Question List

Question 1: Before any exception is used, what is the maximum rating of the short-circuit and ground-fault protective device for a single hermetic motor-compressor?

125% of rated-load current
150% of rated-load current
175% of rated-load current
225% of rated-load current

NEC Reference: NEC 440.22(A)

Question 2: Per the exception in NEC 440.22(A), what is the minimum ampere rating allowed for a motor-compressor short-circuit and ground-fault protective device, even if the calculated value is lower?

10 A
15 A
20 A
25 A

NEC Reference: NEC 440.22(A) Exception

Question 3: What size branch-circuit conductor is required for an 18-ampere motor-compressor connected to a 240-volt circuit, with terminals rated at 75 C?

12 AWG
10 AWG
14 AWG
8 AWG

NEC Reference: NEC 440.32 / Table 310.16

Question 4: What size branch-circuit protection is required for a 20-ampere motor-compressor connected to a 240-volt circuit?

35 A
40 A
45 A
50 A

NEC Reference: NEC 440.22(A)

Question 5: What size branch-circuit conductor is suitable for a 5 HP, 208-volt three-phase motor, with terminals rated 75 C?

12 AWG
10 AWG
8 AWG
14 AWG

NEC Reference: NEC Table 430.250 / Table 310.16

Question 6: An AC general-use snap switch may serve as the controller for a stationary motor rated up to what size (300 V or less)?

2 HP
1 HP
1/2 HP
1/8 HP

NEC Reference: NEC 430.83(C)

Question 7: The branch-circuit overcurrent device of a stationary motor rated below what horsepower may also serve as the motor's controller?

5 HP
3 HP
1 HP
1/8 HP

NEC Reference: NEC 430.81(A)

Question 8: A disconnecting means for motor circuits over 1000 volts must be capable of being locked in which position?

Closed position
Open position
On position
Both open and closed

NEC Reference: NEC 430.109

Question 9: Overload protection is generally required for a motor rated above what horsepower?

1/8 HP
1/4 HP
1/2 HP
1 HP

NEC Reference: NEC 430.32(A)

Question 10: A motor disconnecting means located "within sight" of the motor must be visible and not more than what distance away?

25 feet
50 feet
70 feet
90 feet

NEC Reference: NEC Article 100

Question 11: A separate overload relay protecting a hermetic motor-compressor must trip at not more than what percentage of the rated-load current?

175%
140%
125%
115%

NEC Reference: NEC 440.52(A)(1)

Question 12: Per NEC 440.12(A), a disconnecting means for a hermetic motor-compressor is generally sized based on what percent of the compressor rated-load current, if not horsepower-rated?

115%
125%
100%
175%

NEC Reference: NEC 440.12(A)

Question 13: A cord-and-plug-connected room air conditioner (250 V or less) is the only load on its branch circuit. Its rating must not exceed what percent of the branch-circuit rating?

80%
100%
125%
50%

NEC Reference: NEC 440.62(B)

Question 14: A hermetic refrigerant motor-compressor must be marked with which of the following?

The branch-circuit breaker size
The installation date
The refrigerant line length
Rated-load current and locked-rotor current

NEC Reference: NEC 440.4(A)

Question 15: A motor controller (other than certain inverse-time breakers) must generally have a horsepower rating not lower than what?

The horsepower rating of the motor
Half the motor horsepower
Any rating at all
Twice the motor horsepower, always

NEC Reference: NEC 430.83

Question 16: A 1/2 HP motor is automatically started. What does the NEC require?

Overload protection per 430.32(B)
No overload protection, because it is under 1 HP
Only a fuse in the neutral
Only a manual motor starter

NEC Reference: NEC 430.32(B)

Question 17: A motor disconnecting means must generally be located in sight from what?

The service equipment
The nearest panelboard
The building entrance
The motor location and the driven machinery location

NEC Reference: NEC 430.102(B)(1)

Question 18: Feeder tap conductors supplying a motor circuit are not over 10 ft long and are enclosed in a raceway. What is their minimum ampacity?

Equal to the feeder conductor ampacity
At least 125% of the feeder overcurrent device rating
As required by 430.22, and at least 1/10 of the feeder overcurrent device rating
At least 1/3 of the feeder conductor ampacity

NEC Reference: NEC 430.28(1)

Question 19: Multimotor air-conditioning equipment is marked with a maximum overcurrent protective device rating. How is the branch-circuit protection selected?

Not larger than the marked maximum rating
At any size that holds the starting current
At 125% of the minimum circuit ampacity
At 250% of the largest motor only

NEC Reference: NEC 440.4(B)

Question 20: What is the "branch-circuit selection current" of a hermetic refrigerant motor-compressor?

A marked value used in place of rated-load current when it is larger
The breaker size required by the utility
The current at locked rotor
The current at which the overload relay trips

NEC Reference: NEC 440.2

Question 21: Can a single motor be supplied from a feeder that also supplies other loads, without a separate feeder just for that motor?

Yes, if properly sized
No, every motor needs a dedicated feeder
Only for motors under 1 HP
Only for single-phase motors

NEC Reference: NEC 430.24 / 430.63

Question 22: How must a cord-and-plug-connected room air conditioner be grounded?

It need not be grounded if double-insulated by the installer
Through a separate ground rod at the window
Through the neutral conductor of the cord
In accordance with 250.110, 250.112 and 250.114

NEC Reference: NEC 440.61

Question 23: Where must the disconnecting means for air-conditioning equipment be located?

At the service equipment only
Within sight from, and readily accessible from, the equipment
Within 100 ft of the equipment
Anywhere inside the building

NEC Reference: NEC 440.14

Question 24: On HVAC equipment nameplates, what do the abbreviations MCA and MOCP generally stand for?

Minimum circuit ampacity and maximum overcurrent protection
Motor control assembly and motor overcurrent panel
Nothing standard -- they vary by installer
Maximum current allowed and minimum operating cost

NEC Reference: NEC Article 440

Question 25: Can the same disconnecting means serve both the required motor disconnect and a required equipment disconnect for air-conditioning/refrigeration equipment, when they are the same device?

Yes, if it meets both articles' requirements
No, two separate devices are always required
Only for motors under 1 HP
Only for single-phase equipment

NEC Reference: NEC 440.14 / 430.109

Question 26: Can a thermal protector built into a hermetic motor-compressor serve as the required overload protection?

Yes, if suitable for the application
No, a separate device is always required
Only for motors over 50 HP
Only for three-phase compressors

NEC Reference: NEC 440.52(A)(1)

Question 27: Under NEC 440.22(A), when the calculated motor-compressor short-circuit protective device rating does not correspond to a standard fuse or breaker size, what should be done?

Use the next higher standard rating, within the cap
Leave the equipment unprotected
Always round down, no matter what
Double the value automatically

NEC Reference: NEC 440.22(A)

Question 28: When two or more motor-compressors, or a motor-compressor plus other loads, are supplied by a single branch circuit, how is the branch-circuit conductor generally sized?

125% of the largest, plus the sum of the rest
100% of all loads added together, no multiplier
Only the largest single load, ignoring the rest
A flat 20 amperes regardless of load

NEC Reference: NEC 440.33

Question 29: An individual disconnecting means is required for each motor controller. Where must it be located?

At the service equipment
Inside the motor terminal box
In sight from the controller location
Within 100 ft of the motor

NEC Reference: NEC 430.102(A)

Question 30: An overload device sized at 125% will not let a motor with a 1.15 service factor start. What is the maximum the overload may be increased to?

130% of nameplate current
140% of nameplate current
150% of nameplate current
175% of nameplate current

NEC Reference: NEC 430.32(C)

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 3 (NEC 430/440) — NEC 2020 Edition

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Motor Circuit Calculations 3 (NEC 430/440) — NEC 2020 Edition — Question List

Question 1: Before any exception is used, what is the maximum rating of the short-circuit and ground-fault protective device for a single hermetic motor-compressor?

Question 2: Per the exception in NEC 440.22(A), what is the minimum ampere rating allowed for a motor-compressor short-circuit and ground-fault protective device, even if the calculated value is lower?

Question 3: What size branch-circuit conductor is required for an 18-ampere motor-compressor connected to a 240-volt circuit, with terminals rated at 75 C?

Question 4: What size branch-circuit protection is required for a 20-ampere motor-compressor connected to a 240-volt circuit?

Question 5: What size branch-circuit conductor is suitable for a 5 HP, 208-volt three-phase motor, with terminals rated 75 C?

Question 6: An AC general-use snap switch may serve as the controller for a stationary motor rated up to what size (300 V or less)?

Question 7: The branch-circuit overcurrent device of a stationary motor rated below what horsepower may also serve as the motor's controller?

Question 8: A disconnecting means for motor circuits over 1000 volts must be capable of being locked in which position?

Question 9: Overload protection is generally required for a motor rated above what horsepower?

Question 10: A motor disconnecting means located "within sight" of the motor must be visible and not more than what distance away?

Question 11: A separate overload relay protecting a hermetic motor-compressor must trip at not more than what percentage of the rated-load current?

Question 12: Per NEC 440.12(A), a disconnecting means for a hermetic motor-compressor is generally sized based on what percent of the compressor rated-load current, if not horsepower-rated?

Question 13: A cord-and-plug-connected room air conditioner (250 V or less) is the only load on its branch circuit. Its rating must not exceed what percent of the branch-circuit rating?

Question 14: A hermetic refrigerant motor-compressor must be marked with which of the following?

Question 15: A motor controller (other than certain inverse-time breakers) must generally have a horsepower rating not lower than what?

Question 16: A 1/2 HP motor is automatically started. What does the NEC require?

Question 17: A motor disconnecting means must generally be located in sight from what?

Question 18: Feeder tap conductors supplying a motor circuit are not over 10 ft long and are enclosed in a raceway. What is their minimum ampacity?

Question 19: Multimotor air-conditioning equipment is marked with a maximum overcurrent protective device rating. How is the branch-circuit protection selected?

Question 20: What is the "branch-circuit selection current" of a hermetic refrigerant motor-compressor?

Question 21: Can a single motor be supplied from a feeder that also supplies other loads, without a separate feeder just for that motor?

Question 22: How must a cord-and-plug-connected room air conditioner be grounded?

Question 23: Where must the disconnecting means for air-conditioning equipment be located?

Question 24: On HVAC equipment nameplates, what do the abbreviations MCA and MOCP generally stand for?

Question 25: Can the same disconnecting means serve both the required motor disconnect and a required equipment disconnect for air-conditioning/refrigeration equipment, when they are the same device?

Question 26: Can a thermal protector built into a hermetic motor-compressor serve as the required overload protection?

Question 27: Under NEC 440.22(A), when the calculated motor-compressor short-circuit protective device rating does not correspond to a standard fuse or breaker size, what should be done?

Question 28: When two or more motor-compressors, or a motor-compressor plus other loads, are supplied by a single branch circuit, how is the branch-circuit conductor generally sized?

Question 29: An individual disconnecting means is required for each motor controller. Where must it be located?

Question 30: An overload device sized at 125% will not let a motor with a 1.15 service factor start. What is the maximum the overload may be increased to?

Key NEC References for This Test

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