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.
Free Conductor Protection Practice Questions
Journeyman Electrician License Exam · Overcurrent Protection
This module covers Conductor Protection as part of the Overcurrent Protection section, testing your understanding of core concepts and their practical application.
| Exam | Journeyman Electrician License Exam |
| Pass Rate | 55% |
| Duration | 240 minutes |
| Module | Conductor Protection |
Why Conductor Protection matters
Conductor Protection is one of the most tested NEC topics because improper grounding and protection cause electrical fires and fatalities.
Sample Practice Questions (5)
1. Per NEC 240.4(D), what is the maximum overcurrent protection permitted for 12 AWG copper conductors?
- 15A
- 20A
- 25A
- 30A
2. A 2 AWG THHN copper conductor (90°C ampacity = 130A) is installed in a conduit with 5 other current-carrying conductors (6 total). The adjusted ampacity is used with 75°C terminations. What is the maximum OCPD rating using the next standard size up rule?
- 100A
- 110A
- 90A
- 125A
3. Per NEC 110.14(C)(1), equipment with terminations rated for 60°C requires conductors to be selected based on which ampacity column of Table 310.16?
- The 60°C column, even if the conductor insulation is rated higher
- The 90°C column to maximize ampacity
- The 75°C column as a compromise
- Any column, since the conductor insulation rating determines ampacity
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Start practicing free →4. A 6 AWG copper THWN conductor is installed with 75°C-rated terminals. Per NEC Table 310.16 (75°C column), the ampacity is 65 amperes. What is the maximum standard OCPD size permitted to protect this conductor per 240.4(B)?
- 70 amperes
- 60 amperes
- 65 amperes
- 80 amperes
5. Three 3 AWG THHN copper conductors are installed in a conduit in an ambient temperature of 40°C. Per Table 310.16 (90°C column), the base ampacity is 115A. The temperature correction factor for 40°C in the 90°C column is 0.91. What is the adjusted ampacity, and what OCPD size should be selected assuming 75°C terminals?
- Adjusted ampacity is 104.65A; however, the 75°C column ampacity for 3 AWG is 100A, so the OCPD is sized at 100 amperes
- Adjusted ampacity is 104.65A, so select a 110A OCPD based on the 90°C calculation
- Adjusted ampacity is 115A because temperature correction does not apply to THHN
- Adjusted ampacity is 80A, requiring a 80A OCPD
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