NEC Tables · Grounding

Table 250.122 — EGC sizing

Breaker rating in, equipment grounding conductor out — and the proportional upsize rule that rides along.

Free · NEC 2023 · Updated
8 AWG/kcmil
100 · Copper
minimum EGC per Table 250.122
Exam trapThe EGC never needs to be larger than the circuit conductors themselves — and it sizes from the BREAKER, not the load or the wire. Three different “from” choices, one right one.

The EGC sizes from the rating of the overcurrent device ahead of the circuit. When you upsize circuit conductors for voltage drop, 250.122(B) makes the EGC grow proportionally by circular-mil area — the table is the floor, not always the answer.

Rating or Setting ofAutomatic OvercurrentDevice in Circuit Aheadof Equipment, Conduit, etc., Not Exceeding(Amperes)CopperAluminum orCopper-CladAluminum*
151412
201210
60108
10086
20064
30042
40031
50021/0
60012/0
8001/03/0
10002/04/0
12003/0250
16004/0350
2000250400
2500350600
3000400600
4000500750
50007001250
60008001250
Notes that change the answer — 250.122(G)

Note: Where necessary to comply with 250.4(A)(5) or (B)(4), the equipment grounding conductor shall be sized larger than given in this table.

*See installation restrictions in 250.120.

Values derived from the 2023 National Electrical Code for exam study. Verify installations against the adopted code and local amendments.

Race your codebook — 3 lookups on this table

Q1

A contractor plans to run Type AC cable as the fixed wiring for stage lighting circuits in an assembly occupancy. Which section specifies what size equipment grounding conductor that cable must contain to be an approved method?

  1. A 520.5(A)
  2. B 520.6
  3. C 520.9
  4. D 520.5(D)
Show answer & explanation

Correct: A — 520.5(A)

520.5(A) requires MI, MC, or AC cable used as fixed wiring to contain an insulated equipment grounding conductor sized per Table 250.122. 520.5(D) addresses nonrated construction, not cable grounding conductor sizing, so it doesn't answer this ask.

Q2

An audio system installer runs 14 AWG audio distribution cable (no power-supply conductors) through a metal auxiliary gutter feeding a recording studio's speaker zones. Which section specifies the minimum size equipment grounding conductor required to bond that gutter?

  1. A 640.7(A)
  2. B 640.8
  3. C 640.7(C)
  4. D 640.7(B)
Show answer & explanation

Correct: A — 640.7(A)

640.7(A) is the general grounding rule for wireways and auxiliary gutters and sets the 14 AWG minimum when no power-supply wires are present (sized per 250.122 when they are). 640.7(B) only addresses separately derived systems with 60 volts to ground, and 640.7(C) covers isolated ground receptacles — neither governs bonding the gutter itself.

Q3

A CSST gas piping system installed in a dwelling is likely to become energized due to a possible ground fault. Which section specifies how this metal piping must be bonded and how the bonding jumper is sized?

  1. A 250.104(B)
  2. B 250.104(A)(1)
  3. C 250.106
  4. D 250.104(C)
Show answer & explanation

Correct: A — 250.104(B)

250.104(B) covers bonding of other metal piping systems, including gas piping, that are likely to become energized, and directs sizing to Table 250.122. 250.104(A)(1) governs metal water piping specifically, and 250.104(C) covers structural metal, neither of which applies to gas piping.

Keep going

EGC Sizing — the concept NEC guide Article 250 practice questions 77 questions
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