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NEC 250 Practice Questions: Grounding & Bonding (California Exam)

Article 250 is one of the most-tested and most-confused topics on the California exam. The fix is knowing which table to reach for before you start. Here is the rule, the trap, and an original question worked all the way through.

Last reviewed June 2026

What the exam is really testing

  • Which conductor you are sizing: grounding electrode conductor or equipment grounding conductor.
  • Reading Table 250.66 (GEC, off the service) versus Table 250.122 (EGC, off the breaker).
  • Bonding rules for metal raceways and service equipment.
  • Speed: finding the right table fast in references provided at the test center.

The trap

Candidates grab the wrong table. They use 250.122 for a grounding electrode conductor or 250.66 for an equipment grounding conductor. Decide which conductor you are sizing first, then the table is obvious.

Try an original question

Sample question · original

A 200-amp service is run with 3/0 copper service-entrance conductors.

What size copper grounding electrode conductor does NEC Table 250.66 require?

  • A8 AWG copper
  • B6 AWG copper
  • 4 AWG copper
  • D2 AWG copper

Answer C. Table 250.66 sizes the grounding electrode conductor off the largest service-entrance conductor. Service conductors over 2 AWG through 3/0 copper land on a 4 AWG copper GEC.

  • NEC 2023 Table 250.66

Why the other answers tempt you

  • A: 8 AWG is the equipment grounding conductor for a 60-amp circuit under Table 250.122. Wrong table.
  • B: 6 AWG is the GEC when the service is 1 AWG copper or smaller, not 3/0.
  • D: 2 AWG is the GEC for service conductors larger than 3/0 up to 350 kcmil.

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