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Conductors for General Wiring (NEC 310) — NEC 2023 Edition

Free NEC 2023 practice test on Article 310: conductor ampacity (Table 310.16), temperature correction and adjustment factors, parallel conductors, stranded conductor rules, wet-location conductors, and single-phase dwelling service/feeder sizing. 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 Conductors for General Wiring (NEC 310) — NEC 2023 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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Conductors for General Wiring (NEC 310) — NEC 2023 Edition — Question List

Question 1: When conductors run in parallel the voltage must be evenly distributed between individual conductors.

True
False

NEC Reference: NEC 310.10(H)

Question 2: NEC Table 310.16 lists conductor ampacity based on ambient temperature and how many current-carrying conductors in a raceway or cable?

Three
Six
One
Nine

NEC Reference: NEC Table 310.16

Question 3: Table 310.16 lists conductor ampacity under three temperature-rating columns. What are they?

60 degC, 75 degC, 90 degC
30 degC, 60 degC, 90 degC
50 degC, 70 degC, 100 degC
40 degC, 80 degC, 120 degC

NEC Reference: NEC Table 310.16

Question 4: Under NEC 310.14(A), the allowable ampacity of a conductor is generally determined by which method?

Tables in 310.15, or engineering supervision
Guesswork only
The conductor manufacturer's marketing brochure
A fixed value regardless of conditions

NEC Reference: NEC 310.14(A)

Question 5: When conductors are installed in an ambient temperature different from that assumed in Table 310.16, what must generally be applied?

An ambient temperature correction factor
Nothing -- ampacity never changes
A doubling of conductor size automatically
A different color code

NEC Reference: NEC 310.15(B)

Question 6: When more than three current-carrying conductors are installed in the same raceway or cable, what must generally be applied to the ampacity?

An adjustment factor
No change is ever needed
A minimum wire size of 500 kcmil
A mandatory ground-fault breaker

NEC Reference: NEC 310.15(C)

Question 7: Per NEC 310.3(A), conductors sized 8 AWG and larger installed in a raceway must generally be what?

Stranded
Solid only
Aluminum only
Bare, with no insulation

NEC Reference: NEC 310.3(A)

Question 8: Per NEC 310.8, insulated conductors installed in wet locations must generally be what?

Listed for wet locations (or otherwise protected)
Any conductor type is fine
Solid copper only, no exceptions
Bare conductors only

NEC Reference: NEC 310.8

Question 9: NEC 310.12 provides a simplified conductor sizing table for what specific type of installation?

120/240V single-phase dwelling services and feeders
Three-phase industrial feeders
Medium-voltage conductors
Fixture wires only

NEC Reference: NEC 310.12

Question 10: NEC Table 310.104(A) lists trade name, type letter, and maximum operating temperature for what?

Insulated conductor types (such as THHN, THWN-2, XHHW)
Panelboard bus ratings
Grounding electrode sizes
Transformer impedance values

NEC Reference: NEC Table 310.104(A)

Question 11: What is the maximum operating temperature rating of THHN insulation in a dry location, per NEC Table 310.104(A)?

90 degC
60 degC
75 degC
105 degC

NEC Reference: NEC Table 310.104(A)

Question 12: Per NEC 310.10(H), conductors 1/0 AWG and larger, when electrically joined at both ends to form a single conductor, are generally called what?

Parallel conductors
Series conductors
Bonding jumpers
Isolated conductors

NEC Reference: NEC 310.10(H)

Question 13: For a set of parallel conductors to share current evenly, per NEC 310.10(H), what must be true about each conductor's length?

They must all be the same length
Length does not matter at all
They must differ by exactly 10%
Only the longest one matters

NEC Reference: NEC 310.10(H)

Question 14: Can a set of parallel conductors mix copper and aluminum conductors together, per NEC 310.10(H)?

No, they must be the same material
Yes, freely mixed
Only if lengths differ
Only in wet locations

NEC Reference: NEC 310.10(H)

Question 15: When a conductor is terminated on equipment rated for only 60 degC or 75 degC, the ampacity used is generally limited to what, even if the conductor insulation is rated higher?

The lowest temperature rating of any termination/equipment in the circuit
Always the conductor insulation's full rating
There is no such limitation
Always 90 degC, regardless of equipment

NEC Reference: NEC 110.14(C)

Question 16: A 90 degC-rated conductor is commonly used with correction and adjustment factors applied to its 90 degC ampacity, but the FINAL selected ampacity is then capped at what?

The equipment termination temperature rating
The 90 degC ampacity, with no cap
Always exactly half the 90 degC value
There is never a final cap

NEC Reference: NEC 110.14(C) / 310.14

Question 17: A grounded (neutral) conductor sized 6 AWG or smaller is generally identified by what color(s) of insulation?

White or gray
Black
Red
Blue

NEC Reference: NEC 200.6(A)

Question 18: What is generally the smallest copper conductor size permitted for general branch-circuit wiring in a dwelling?

14 AWG
18 AWG
10 AWG
6 AWG

NEC Reference: NEC 240.4(D) / general practice

Question 19: Per Table 310.16, what is the base ampacity of a 4 AWG copper conductor in the 75 degC column?

85 amperes
70 amperes
95 amperes
65 amperes

NEC Reference: NEC Table 310.16

Question 20: Per Table 310.16, what is the base ampacity of a 2 AWG copper conductor in the 90 degC column?

130 amperes
115 amperes
145 amperes
100 amperes

NEC Reference: NEC Table 310.16

Question 21: Per NEC Table 310.15(C)(1), what adjustment factor applies when 4 to 6 current-carrying conductors are bundled together in a raceway?

80%
70%
100%
50%

NEC Reference: NEC Table 310.15(C)(1)

Question 22: Per NEC 310.8, conductors exposed to corrosive conditions (fumes, vapors, etc.) must generally be what?

Suitable for the corrosive condition, or protected
Any general-purpose conductor is fine
Bare copper only
No special provision is needed

NEC Reference: NEC 310.8

Question 23: Insulated conductors are generally required to be durably marked at intervals with which of the following?

Conductor size, insulation type, and voltage rating
Nothing is required
Only the manufacturer's logo
Only the purchase date

NEC Reference: NEC 310.120

Question 24: Ampacity determined "under engineering supervision," per NEC 310.14(A)(2), generally means what?

Ampacity calculated by a qualified engineer using recognized methods
Guessing based on wire color
Always using the smallest possible wire
Something that is never permitted

NEC Reference: NEC 310.14(A)(2)

Question 25: For the same AWG size and temperature rating, how does the ampacity of an aluminum conductor generally compare to a copper conductor, per Table 310.16?

Aluminum ampacity is lower
Aluminum ampacity is higher
They are always identical
Aluminum has no ampacity rating

NEC Reference: NEC Table 310.16

Question 26: Conductors intended for direct burial in the earth must generally be of what type?

Listed/identified for direct burial
Any general-purpose type
Bare aluminum only
Fixture wire only

NEC Reference: NEC 310.10(F) / 300.5

Question 27: Per NEC 310.15(B)(2), conductors installed in raceways exposed to direct sunlight on or above a rooftop generally require what type of adjustment?

An added ambient temperature correction
No adjustment is ever needed
A mandatory doubling of wire size
A GFCI breaker only

NEC Reference: NEC 310.15(B)(2)

Question 28: NEC Article 310 generally covers general requirements for which type of conductors, per its scope in 310.1?

Insulated, covered, and bare general-wiring conductors
Only medium-voltage cables
Only fiber optic cables
Only grounding electrode conductors

NEC Reference: NEC 310.1

Question 29: XHHW insulated conductors are generally suitable for use in which locations, per NEC Table 310.104(A)?

Both dry and wet locations
Dry locations only
Wet locations only, never dry
It is not a recognized type

NEC Reference: NEC Table 310.104(A)

Question 30: In addition to matching length, material, and size, what else must generally match across a set of parallel conductors, per NEC 310.10(H)?

Insulation type and termination method
Nothing else needs to match
Only the manufacturer brand
Only the shipping date

NEC Reference: NEC 310.10(H)

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.

Conductors for General Wiring (NEC 310) — NEC 2023 Edition

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Key NEC References for This Test

Conductors for General Wiring (NEC 310) — NEC 2023 Edition

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Conductors for General Wiring (NEC 310) — NEC 2023 Edition — Question List

Question 1: When conductors run in parallel the voltage must be evenly distributed between individual conductors.

Question 2: NEC Table 310.16 lists conductor ampacity based on ambient temperature and how many current-carrying conductors in a raceway or cable?

Question 3: Table 310.16 lists conductor ampacity under three temperature-rating columns. What are they?

Question 4: Under NEC 310.14(A), the allowable ampacity of a conductor is generally determined by which method?

Question 5: When conductors are installed in an ambient temperature different from that assumed in Table 310.16, what must generally be applied?

Question 6: When more than three current-carrying conductors are installed in the same raceway or cable, what must generally be applied to the ampacity?

Question 7: Per NEC 310.3(A), conductors sized 8 AWG and larger installed in a raceway must generally be what?

Question 8: Per NEC 310.8, insulated conductors installed in wet locations must generally be what?

Question 9: NEC 310.12 provides a simplified conductor sizing table for what specific type of installation?

Question 10: NEC Table 310.104(A) lists trade name, type letter, and maximum operating temperature for what?

Question 11: What is the maximum operating temperature rating of THHN insulation in a dry location, per NEC Table 310.104(A)?

Question 12: Per NEC 310.10(H), conductors 1/0 AWG and larger, when electrically joined at both ends to form a single conductor, are generally called what?

Question 13: For a set of parallel conductors to share current evenly, per NEC 310.10(H), what must be true about each conductor's length?

Question 14: Can a set of parallel conductors mix copper and aluminum conductors together, per NEC 310.10(H)?

Question 15: When a conductor is terminated on equipment rated for only 60 degC or 75 degC, the ampacity used is generally limited to what, even if the conductor insulation is rated higher?

Question 16: A 90 degC-rated conductor is commonly used with correction and adjustment factors applied to its 90 degC ampacity, but the FINAL selected ampacity is then capped at what?

Question 17: A grounded (neutral) conductor sized 6 AWG or smaller is generally identified by what color(s) of insulation?

Question 18: What is generally the smallest copper conductor size permitted for general branch-circuit wiring in a dwelling?

Question 19: Per Table 310.16, what is the base ampacity of a 4 AWG copper conductor in the 75 degC column?

Question 20: Per Table 310.16, what is the base ampacity of a 2 AWG copper conductor in the 90 degC column?

Question 21: Per NEC Table 310.15(C)(1), what adjustment factor applies when 4 to 6 current-carrying conductors are bundled together in a raceway?

Question 22: Per NEC 310.8, conductors exposed to corrosive conditions (fumes, vapors, etc.) must generally be what?

Question 23: Insulated conductors are generally required to be durably marked at intervals with which of the following?

Question 24: Ampacity determined "under engineering supervision," per NEC 310.14(A)(2), generally means what?

Question 25: For the same AWG size and temperature rating, how does the ampacity of an aluminum conductor generally compare to a copper conductor, per Table 310.16?

Question 26: Conductors intended for direct burial in the earth must generally be of what type?

Question 27: Per NEC 310.15(B)(2), conductors installed in raceways exposed to direct sunlight on or above a rooftop generally require what type of adjustment?

Question 28: NEC Article 310 generally covers general requirements for which type of conductors, per its scope in 310.1?

Question 29: XHHW insulated conductors are generally suitable for use in which locations, per NEC Table 310.104(A)?

Question 30: In addition to matching length, material, and size, what else must generally match across a set of parallel conductors, per NEC 310.10(H)?

Key NEC References for This Test

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