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

Free GEC Sizing (Table 250.66) Practice Questions

Journeyman Electrician License Exam · Grounding & Bonding

This module covers GEC Sizing (Table 250.66) as part of the Grounding & Bonding section, testing your understanding of core concepts and their practical application.

ExamJourneyman Electrician License Exam
Pass Rate55%
Duration240 minutes
ModuleGEC Sizing (Table 250.66)

Why GEC Sizing (Table 250.66) matters

GEC Sizing (Table 250.66) is heavily tested because undersized conductors and services cause overheating, fires, and equipment failure.

Sample Practice Questions (5)

1. A 200-ampere service is supplied by two sets of 3/0 AWG copper conductors in parallel. Per NEC Table 250.66, the equivalent single conductor area is used to size the GEC. 3/0 AWG copper = 167,800 CM. Two sets = 335,600 CM, which is closest to 350 kcmil. The minimum copper GEC is:

  • 4 AWG
  • 2 AWG
  • 1/0 AWG
  • 6 AWG

2. Per NEC Table 250.66, if the largest ungrounded service-entrance conductor is 1000 kcmil copper, the minimum size copper GEC is:

  • 1/0 AWG
  • 2/0 AWG
  • 3/0 AWG
  • 4/0 AWG

3. Per NEC 250.64(E), when a grounding electrode conductor (GEC) is enclosed in a ferromagnetic (steel/iron) raceway, the raceway shall be:

  • Grounded at one end only
  • Bonded to the GEC at both ends of the raceway
  • Painted to prevent corrosion
  • No larger than 1 inch trade size

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4. A 1600-ampere service uses four sets of 500 kcmil copper service-entrance conductors per phase. Per the note to NEC Table 250.66, when service-entrance conductors exceed 1100 kcmil copper, the GEC shall be not less than _____ of the equivalent area of the largest ungrounded conductor.

  • 10%
  • 12.5%
  • 15%
  • 20%

5. Per NEC Table 250.66, if the largest ungrounded service-entrance conductor is 4/0 AWG aluminum, the minimum size copper GEC is:

  • 6 AWG
  • 4 AWG
  • 2 AWG
  • 8 AWG

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Frequently Asked Questions

How many GEC Sizing (Table 250.66) questions are on the Journeyman Electrician License Exam?▼
The Grounding & Bonding section, which includes GEC Sizing (Table 250.66), 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 GEC Sizing (Table 250.66)?▼
Practice solving calculation problems daily rather than just reading formulas. Work through problems step-by-step, check your units, and time yourself to build speed and accuracy under exam conditions.
What topics within GEC Sizing (Table 250.66) 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.