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Conductors for General Wiring (NEC 310) — NEC 2020 Edition

Free NEC 2020 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 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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Conductors for General Wiring (NEC 310) — NEC 2020 Edition — Question List

Question 1: True or false: when conductors are run in parallel, the CURRENT (not voltage) must be evenly distributed between the individual conductors.

True
False
Only for aluminum conductors
Only in wet locations

NEC Reference: NEC 310.10(H)

Question 2: NEC Table 310.16 provides base conductor ampacity assuming no more than how many current-carrying conductors in a raceway, cable, or earth?

Three
Six
One
Nine

NEC Reference: NEC Table 310.16

Question 3: Which three insulation temperature ratings are used as column headers in Table 310.16?

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: Per NEC 310.14(A), how may the allowable ampacity of a conductor generally be determined?

Tables in 310.15, or engineering supervision
Guesswork only
A marketing brochure
A fixed value regardless of conditions

NEC Reference: NEC 310.14(A)

Question 5: If the ambient temperature at an installation differs from that assumed in Table 310.16, what must generally be applied to the ampacity?

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 share 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), what construction is generally required for 8 AWG and larger conductors installed in a raceway?

Stranded
Solid only
Aluminum only
Bare, with no insulation

NEC Reference: NEC 310.3(A)

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

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: What specific type of installation does the simplified conductor sizing table at NEC 310.12 apply to?

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: Which NEC table lists conductor insulation types such as THHN, THWN-2, and XHHW, along with their maximum operating temperatures?

Table 310.104(A)
Table 250.66
Table 220.42
Table 430.250

NEC Reference: NEC Table 310.104(A)

Question 11: THHN insulation is generally rated for what maximum temperature in a dry location?

90 degC
60 degC
75 degC
105 degC

NEC Reference: NEC Table 310.104(A)

Question 12: Per NEC 310.10(H), what is generally the minimum conductor size permitted to be run in parallel?

1/0 AWG
14 AWG
8 AWG
4/0 AWG

NEC Reference: NEC 310.10(H)

Question 13: For a set of parallel conductors to carry current evenly, per NEC 310.10(H), what must generally be true about their 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: Under NEC 310.10(H), can a single parallel set mix copper and aluminum conductors?

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: A 90 degC-rated conductor terminates on a breaker rated only for 75 degC terminations. Per NEC 110.14(C), what ampacity must generally be used?

The 75 degC ampacity (the lowest rated termination)
The full 90 degC ampacity
The 60 degC ampacity, always
There is no limitation

NEC Reference: NEC 110.14(C)

Question 16: When applying correction and adjustment factors to a 90 degC-rated conductor, the resulting ampacity is still ultimately capped by 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 6 AWG or smaller is generally required to be identified by what?

White or gray insulation
Black insulation
Red insulation
Blue insulation

NEC Reference: NEC 200.6(A)

Question 18: For a standard 15-ampere general-purpose branch circuit, what is generally the smallest copper conductor size used?

14 AWG
18 AWG
10 AWG
6 AWG

NEC Reference: NEC 240.4(D)

Question 19: Per Table 310.16, what is the base ampacity of a 4 AWG copper conductor at 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 at the 90 degC column?

130 amperes
115 amperes
145 amperes
100 amperes

NEC Reference: NEC Table 310.16

Question 21: Per Table 310.15(C)(1), what adjustment factor generally applies to 4-6 current-carrying conductors bundled 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 fumes or vapors 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 regular intervals, with which information?

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: What does it mean for conductor ampacity to be determined "under engineering supervision," per NEC 310.14(A)(2)?

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, is aluminum conductor ampacity generally higher, lower, or the same as copper, per Table 310.16?

Lower
Higher
Always identical
Aluminum has no ampacity rating

NEC Reference: NEC Table 310.16

Question 26: Conductors that will be directly buried in the earth must generally be 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), what generally must be applied to conductors in raceways exposed to direct sunlight on a rooftop?

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: Per its scope in NEC 310.1, Article 310 generally covers general requirements for which conductors?

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: Per NEC Table 310.104(A), XHHW insulated conductors are generally suitable for which locations?

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: Besides 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 2020 Edition

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Key NEC References for This Test

Conductors for General Wiring (NEC 310) — NEC 2020 Edition

How this test works

Frequently Asked Questions

Is this Conductors for General Wiring (NEC 310) — NEC 2020 Edition free?

What is the NEC code book?

Which NEC edition should I study?

What articles are covered on electrician licensing exams?

How to Use This Practice Test

Student Reviews

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Conductors for General Wiring (NEC 310) — NEC 2020 Edition — Question List

Question 1: True or false: when conductors are run in parallel, the CURRENT (not voltage) must be evenly distributed between the individual conductors.

Question 2: NEC Table 310.16 provides base conductor ampacity assuming no more than how many current-carrying conductors in a raceway, cable, or earth?

Question 3: Which three insulation temperature ratings are used as column headers in Table 310.16?

Question 4: Per NEC 310.14(A), how may the allowable ampacity of a conductor generally be determined?

Question 5: If the ambient temperature at an installation differs from that assumed in Table 310.16, what must generally be applied to the ampacity?

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

Question 7: Per NEC 310.3(A), what construction is generally required for 8 AWG and larger conductors installed in a raceway?

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

Question 9: What specific type of installation does the simplified conductor sizing table at NEC 310.12 apply to?

Question 10: Which NEC table lists conductor insulation types such as THHN, THWN-2, and XHHW, along with their maximum operating temperatures?

Question 11: THHN insulation is generally rated for what maximum temperature in a dry location?

Question 12: Per NEC 310.10(H), what is generally the minimum conductor size permitted to be run in parallel?

Question 13: For a set of parallel conductors to carry current evenly, per NEC 310.10(H), what must generally be true about their length?

Question 14: Under NEC 310.10(H), can a single parallel set mix copper and aluminum conductors?

Question 15: A 90 degC-rated conductor terminates on a breaker rated only for 75 degC terminations. Per NEC 110.14(C), what ampacity must generally be used?

Question 16: When applying correction and adjustment factors to a 90 degC-rated conductor, the resulting ampacity is still ultimately capped by what?

Question 17: A grounded (neutral) conductor 6 AWG or smaller is generally required to be identified by what?

Question 18: For a standard 15-ampere general-purpose branch circuit, what is generally the smallest copper conductor size used?

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

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

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

Question 22: Per NEC 310.8, conductors exposed to corrosive fumes or vapors must generally be what?

Question 23: Insulated conductors are generally required to be durably marked, at regular intervals, with which information?

Question 24: What does it mean for conductor ampacity to be determined "under engineering supervision," per NEC 310.14(A)(2)?

Question 25: For the same AWG size and temperature rating, is aluminum conductor ampacity generally higher, lower, or the same as copper, per Table 310.16?

Question 26: Conductors that will be directly buried in the earth must generally be what type?

Question 27: Per NEC 310.15(B)(2), what generally must be applied to conductors in raceways exposed to direct sunlight on a rooftop?

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

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

Question 30: Besides 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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