TL;DR

Master conductor sizing, ampacity calculations, and derating factors per NEC tables. Wire sizing is fundamental to electrical safety and one of the most tested exam topics.

By Valenke Exam Prep Team·Last updated 2026-06-03

Free Conductor Ampacity (Table 310.16) Practice Questions

Journeyman Electrician License Exam · Wiring Methods & Materials

This module covers Conductor Ampacity (Table 310.16) as part of the Wiring Methods & Materials section, testing your understanding of core concepts and their practical application.

Exam	Journeyman Electrician License Exam
Pass Rate	55%
Duration	240 minutes
Module	Conductor Ampacity (Table 310.16)

Why Conductor Ampacity (Table 310.16) matters

Conductor Ampacity (Table 310.16) is heavily tested because undersized conductors and services cause overheating, fires, and equipment failure.

Sample Practice Questions (5)

1. Eight 10 AWG THHN copper conductors are installed in a single conduit in an ambient temperature of 40°C. Per Table 310.16 and the applicable correction/adjustment factors, what is the adjusted ampacity of each conductor? (90°C base ampacity of 10 AWG = 40A; 40°C correction factor for 90°C = 0.91; adjustment for 8 CCC = 70%)

25.48 amperes
28 amperes
32 amperes
36.4 amperes

2. A conduit contains three 3-wire circuits (9 current-carrying conductors) of 8 AWG THHN copper. The ambient temperature is 30°C. What is the adjusted ampacity per conductor? (90°C base for 8 AWG = 55A; adjustment for 7-9 CCC = 70%)

38.5 amperes
55 amperes
44 amperes
27.5 amperes

3. Six 6 AWG THHN copper conductors (90°C, 75A each) are installed in a conduit in an ambient temperature of 45°C. What is the adjusted ampacity? (45°C correction for 90°C = 0.87; 6 CCC adjustment = 80%)

52.2 amperes
60 amperes
65.25 amperes
45.68 amperes

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4. Per NEC 240.4(D), what is the maximum overcurrent protection permitted for 14 AWG copper conductors?

15 amperes
20 amperes
25 amperes
30 amperes

5. A 4 AWG THWN-2 copper conductor has a 90°C ampacity of 95A per Table 310.16. However, the termination at the equipment is rated for 75°C only. What ampacity must be used for this conductor per NEC 110.14(C)?

85 amperes (75°C column value)
95 amperes (90°C column value)
70 amperes (60°C column value)
100 amperes

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Frequently Asked Questions

How many Conductor Ampacity (Table 310.16) questions are on the Journeyman Electrician License Exam?▼

The Wiring Methods & Materials section, which includes Conductor Ampacity (Table 310.16), typically represents a significant portion of the exam. Focus on understanding core concepts rather than memorizing exact question counts, as the exam uses adaptive testing.

What is the best way to study Conductor Ampacity (Table 310.16)?▼

Use active recall and spaced repetition rather than passive reading. Practice with realistic exam questions, review explanations for both correct and incorrect answers, and focus on understanding the reasoning behind each concept.

What topics within Conductor Ampacity (Table 310.16) should I focus on most?▼

Focus on the concepts that appear in our practice questions and any areas where you consistently score below 70%. The adaptive practice mode will automatically target your weak areas for efficient study.