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

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

NEC Reference: NEC 310.10(G)

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

Only from manufacturer data sheets
Only from Table 310.12
Only by the authority having jurisdiction at inspection
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?

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

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

NEC Reference: NEC 310.15(C)(1)

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

Solid
Compact aluminum
Stranded
Copper-clad aluminum

NEC Reference: NEC 310.3(C)

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

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

NEC Reference: NEC 310.10(C)

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

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

NEC Reference: NEC Table 310.4(1)

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 310.4(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%
They must all be the same length
Only the neutral conductors must match
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?

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

NEC Reference: NEC 310.10(G)

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) / 310.3(A)

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

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

NEC Reference: NEC 310.10(F)

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

Installation date and size
Ampacity at 75 °C and length
Only the conductor 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 table value is reduced by 20% for safety
The inspector selects the ampacity on site
The 60 °C column is always used

NEC Reference: NEC 310.14

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 that will be buried directly in the earth must be of what type?

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

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: 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 310.4(1)

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

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

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 2023 Edition

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Conductors for General Wiring (NEC 310) — NEC 2023 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 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: 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: NEC 310.12 provides a simplified conductor sizing table for what specific type of installation?

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

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: 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: 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, how does the ampacity of an aluminum conductor generally compare to a copper conductor, 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: 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: 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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