Practice question · NEC Table 250.122

What Size Equipment Grounding Conductor for a 150 Amp Circuit?

By Mason Garry, Master Electrician · October 22, 2026 · 2 min read

What size equipment grounding conductor for a 150 amp circuit is a between-the-rows question. Table 250.122 does not have a 150-amp row waiting for you, and the rule for that gap decides the answer before you ever land on a wire size. Read the table the way the Code tells you to read it, and this one is fast.

Answer: B) 6 AWG. 150 amps falls between rows in Table 250.122, so you use the next higher row — 200 amps — and that row calls for 6 AWG copper.

Where to Find It

Open your Code book to Table 250.122 in Article 250. Look for the 150-amp rating and you will not find it as its own row. That is the whole question. Table 250.122 handles it this way: 150 amps falls between rows, so you use the next higher row — 200 amps — and the 200-amp row gives you 6 AWG copper. Tab it exactly like that in your book: Article 250, "Table 250.122" — "between rows, go up."

Why 6 AWG

Step one is accepting what the stem is really testing. It does not ask you to memorize a wire size. It asks whether you know what to do when the rating in the stem is not printed in the table. The move is always the same: go up to the next higher row. Never down, never to the closest row. Up.

Run the options against that rule. The next higher row from 150 amps is 200 amps, and 200 amps = 6 AWG copper. That is option B. Option A, 8 AWG, is what a smaller row would give you — it is the round-down answer, and rounding down undersizes the equipment grounding conductor. Options C and D, 4 AWG and 3 AWG, are bigger than the table requires. The question asks for the minimum, and the minimum the Code permits here is set by the 200-amp row: 6 AWG.

Do not confuse this table with the grounding electrode conductor table. The equipment grounding conductor lives in Table 250.122. The grounding electrode conductor follows the service conductors in Table 250.66 — we drill that read in the 500 kcmil grounding electrode conductor question. Two tables, two jobs. Match the noun in the stem to the table before you read a single row.

The Trap

The trap is the word "minimum." It pulls you toward the smaller wire, 8 AWG. But minimum does not mean smallest option on the page. It means the smallest conductor the Code permits, and the Code sets that floor at the next higher row. Between rows, go up — that one habit answers this entire family of questions.

Exam Tip

When a Table 250.122 stem uses a rating you cannot find in the table, stop hunting. You have already been given the test: find the next higher row and read across. Write "between rows, go up" on your Table 250.122 tab and this becomes a ten-second question on test day.

Keep Drilling

This is one of 33 NEC topics. Sparky's 1,087 codebook-first questions drill all of them — every question a lookup rep with your book open, 15 minutes a day.