What does NEC Article 250 say about grounding requirements?

Article 250 of the NEC 2023 covers two different jobs that often get mixed up in the field: system grounding, which connects the electrical system to earth, and equipment grounding, which gives fault current a low impedance path back to the source so breakers trip. Section 250.4(A) lays out the performance goals, and the rest of the article tells you how to hit them.

The grounding electrode system

Section 250.50 requires every electrode present at a building to be bonded together into one grounding electrode system. That includes metal underground water pipe with 10 ft or more in contact with earth, concrete encased electrodes (Ufer), ground rings, building steel that qualifies, and rod, pipe, or plate electrodes. If none are present, you install one, and a single rod must show 25 ohms or less or be supplemented by a second rod per 250.53(A)(2). Most crews just drive two rods at least 6 ft apart and skip the resistance test.

Sizing the conductors

The grounding electrode conductor is sized from Table 250.66 based on the service entrance conductors. For a typical 200 amp residential service with 2/0 copper, that means a #4 copper GEC, though the connection to a rod electrode never needs to be larger than #6 copper per 250.66(A). Equipment grounding conductors are sized from Table 250.122 based on the overcurrent device: #12 copper for a 20 amp breaker, #10 for 30 amps, #8 for 60 amps, and #6 for 100 amps.

Bonding is the other half

Section 250.90 and the sections that follow require bonding of enclosures, raceways, and equipment so the fault path stays continuous. The main bonding jumper at the service ties the neutral to the enclosure per 250.24(B), and that is the only place neutrals and grounds land together. Downstream in subpanels they stay separated, with the neutral bar isolated from the can.

Remember 250.24(A)(5): grounding connections to the neutral on the load side of the service disconnect are a violation. That one line explains most inspector red tags on subpanel installs.