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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: Why must conductors in a parallel set be the same length, material, size and insulation, and be terminated the same way?

So the voltage at each end is different
So the current divides evenly among them
So each conductor can have its own breaker
So they can be smaller than 1/0 AWG

NEC Reference: NEC 310.10(G)

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: How may the allowable ampacity of a conductor be determined under 310.14(A)?

Only by the authority having jurisdiction at inspection
Only from Table 310.12
Only from manufacturer data sheets
From Tables 310.16 through 310.21, or under engineering supervision

NEC Reference: NEC 310.14(A)

Question 5: Conductors are installed where the ambient temperature differs from the 30 °C basis of Table 310.16. What must be applied to the table ampacity?

The 125% continuous-load factor
An adjustment factor for the number of conductors
A voltage drop factor
An ambient temperature correction factor

NEC Reference: NEC 310.15(B)

Question 6: More than three current-carrying conductors are installed in one raceway. What must be applied to their ampacity?

Nothing, if the conductors are 90 °C rated
An adjustment factor from Table 310.15(C)(1)
An ambient temperature correction factor only
The 125% continuous-load factor

NEC Reference: NEC 310.15(C)(1)

Question 7: Conductors 8 AWG and larger installed in a raceway must be of what construction?

Stranded
Solid
Copper-clad aluminum
Compact aluminum

NEC Reference: NEC 310.3(C)

Question 8: Insulated conductors installed in a wet location must be of what type?

Bare copper only
Any type with 75 °C insulation
A type listed for use in wet locations
Type THHN

NEC Reference: NEC 310.10(C)

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 with their maximum operating temperatures and permitted locations?

Table 310.15(C)(1)
Table 250.66
Table 310.16
Table 310.4(1)

NEC Reference: NEC Table 310.4(1)

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 310.4(1)

Question 12: What is the minimum conductor size that may generally be connected in parallel?

1/0 AWG
2 AWG
4 AWG
4/0 AWG

NEC Reference: NEC 310.10(G)

Question 13: What must be true about the length of each conductor in a parallel set?

They may differ by up to 10%
Only the neutral conductors must match
They must all be the same length
The longest may be twice the shortest

NEC Reference: NEC 310.10(G)

Question 14: May one set of parallel conductors mix copper and aluminum conductors?

Yes, for the neutral conductors only
No, all conductors in the set must be the same material
Yes, if the aluminum is one size larger
Yes, in sizes 4/0 AWG and larger

NEC Reference: NEC 310.10(G)

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) / 310.3(A)

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: Conductors will be exposed to oils, vapors or gases that harm conductor insulation. What does the NEC require?

A conductor type suitable for that condition
Aluminum conductors only
Bare copper conductors
Any 90 °C rated conductor

NEC Reference: NEC 310.10(F)

Question 23: Which information must be marked on insulated conductors?

Only the conductor size
Ampacity at 75 °C and length
Installation date and size
Maximum voltage, type letters, manufacturer and size

NEC Reference: NEC 310.8

Question 24: What does it mean for conductor ampacity to be determined "under engineering supervision"?

A qualified engineer calculates it with recognized formulas
The inspector selects the ampacity on site
The 60 °C column is always used
The table value is reduced by 20% for safety

NEC Reference: NEC 310.14

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 buried directly in the earth must be of what type?

THHN in a plastic sleeve
Any type with a 90 °C wet rating
A type identified for direct burial
Fixture wire

NEC Reference: NEC 310.10(E)

Question 27: A raceway in direct sunlight sits on a rooftop with less than 7/8 in. between the raceway and the roof. What temperature must be added to the outdoor ambient?

17 °C (30 °F)
22 °C (40 °F)
33 °C (60 °F)
40 °C (72 °F)

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 310.4(1)

Question 30: Besides length, material and size, what else must be the same for every conductor in a parallel set?

Outer jacket color
Insulation type and termination method
Date of manufacture
Manufacturer and reel number

NEC Reference: NEC 310.10(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.

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

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

Question 1: Why must conductors in a parallel set be the same length, material, size and insulation, and be terminated the same way?

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: How may the allowable ampacity of a conductor be determined under 310.14(A)?

Question 5: Conductors are installed where the ambient temperature differs from the 30 °C basis of Table 310.16. What must be applied to the table ampacity?

Question 6: More than three current-carrying conductors are installed in one raceway. What must be applied to their ampacity?

Question 7: Conductors 8 AWG and larger installed in a raceway must be of what construction?

Question 8: Insulated conductors installed in a wet location must be of what type?

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 with their maximum operating temperatures and permitted locations?

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

Question 12: What is the minimum conductor size that may generally be connected in parallel?

Question 13: What must be true about the length of each conductor in a parallel set?

Question 14: May one set of parallel conductors 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: Conductors will be exposed to oils, vapors or gases that harm conductor insulation. What does the NEC require?

Question 23: Which information must be marked on insulated conductors?

Question 24: What does it mean for conductor ampacity to be determined "under engineering supervision"?

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 buried directly in the earth must be of what type?

Question 27: A raceway in direct sunlight sits on a rooftop with less than 7/8 in. between the raceway and the roof. What temperature must be added to the outdoor ambient?

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 length, material and size, what else must be the same for every conductor in a parallel set?

Key NEC References for This Test

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