NEC ReferenceNEC 2023 · 2026 · Updated May 2026

NEC Article 250: Grounding and Bonding

NEC Article 250: Grounding & Bonding covers vs Bonding through Bonding of Metal Piping. This guide explains each section with practical interpretation, common mistakes, and how these rules apply to real projects.

Grounding vs Bonding

Grounding and bonding serve different purposes. Grounding connects the electrical system to earth through electrodes (ground rods, UFER) for lightning protection and voltage stabilization. Bonding connects all metal parts together to ensure fault current has a low-impedance path back to the source so the breaker trips quickly.

Bonding is actually more important for shock protection: a ground rod alone has far too much resistance to trip a breaker during a fault. The breaker trips because fault current flows through the bonded equipment grounding conductor (EGC) back to the panel, not through the earth.

Understanding this distinction is essential for safe electrical work.

250.122 Equipment Grounding Conductor (EGC)

The equipment grounding conductor (green or bare wire) provides the fault-current return path from equipment back to the panel. NEC Table 250.122 sizes the EGC based on the overcurrent device rating: 15A = 14 AWG, 20A = 12 AWG, 30A = 10 AWG, 40-60A = 10 AWG, 100A = 8 AWG, 200A = 6 AWG copper.

When using NM-B cable, the included bare ground wire already meets these minimums. Important: if you upsize circuit conductors for voltage drop, the EGC must be proportionally upsized per 250.122(B). Multiply the minimum EGC cross-sectional area by the ratio of actual conductor area to minimum required conductor area.

See our ground wire sizing guides for pre-computed sizes by breaker rating.

250.66 Grounding Electrode Conductor (GEC)

The grounding electrode conductor connects the main panel to the grounding electrode system. It is sized from NEC Table 250.66 based on the largest service-entrance conductor: 2 AWG or smaller service = 8 AWG GEC, 1/0 service = 6 AWG GEC, 2/0 or 3/0 service = 4 AWG GEC, over 3/0 through 350 kcmil = 2 AWG GEC copper.

For a typical 200A dwelling service with 4/0 aluminum entrance conductors, the GEC is 4 AWG copper. Do not confuse Table 250.66 (GEC sizing, based on service conductor size) with Table 250.122 (EGC sizing, based on breaker rating). Mixing these two tables is the most common grounding error on service upgrades.

250.52-56 Grounding Electrodes

NEC 250.52 lists acceptable grounding electrodes. The concrete-encased electrode (UFER ground) is the most effective: 20 or more feet of bare #4 copper or #4 rebar encased in at least 2 inches of concrete in a building foundation. A metal underground water pipe qualifies if at least 10 feet of metal pipe is in direct contact with earth.

Ground rods must be at least 8 feet long and driven full depth per 250.53(G). A single ground rod that does not achieve 25 ohms resistance to earth must be supplemented by a second rod per 250.56, spaced at least 6 feet apart. In new construction, the UFER ground is usually installed during the foundation pour and is the most reliable long-term electrode.

250.104 Bonding of Metal Piping

All metal piping systems that may become energized must be bonded to the electrical system. Metal water piping requires bonding per 250.104(A), sized from Table 250.66 based on the service conductor size. Interior metal gas piping must be bonded per 250.104(B), sized per Table 250.122 based on the circuit most likely to energize the pipe.

Corrugated stainless steel tubing (CSST) for gas requires bonding per the manufacturer installation instructions, which typically require a minimum 6 AWG copper bonding conductor connected to the grounding electrode system. CSST bonding has been a major focus area for inspectors and insurance companies because unbonded CSST can be punctured by lightning-induced arcing.

Key NEC Tables Referenced

Frequently Asked Questions

What does NEC Article 250 cover?

Article 250 covers grounding & bonding requirements. Key sections include Grounding vs Bonding and 250.122 Equipment Grounding Conductor (EGC). It applies to all electrical installations in the United States.

Where can I find the full text of Article 250?

The full NEC is published by NFPA and available at nfpa.org. Many libraries provide free access. Your local building department also has copies available for reference during permit applications.

Does Article 250 apply to existing wiring?

The NEC applies to new installations, modifications, and additions. Existing wiring that was code-compliant when installed is generally grandfathered unless a renovation triggers an upgrade requirement. Check with your local AHJ (authority having jurisdiction).

When did the current Article 250 requirements take effect?

NEC 2026 is the latest published edition (effective September 2025). NEC 2023 remains the most widely adopted edition by states. Adoption varies - check your state adoption status on our state code pages.

Requirements vary by state. NEC edition, licensing, permits, and GFCI rules differ by jurisdiction. Check your state or pick it below for personalized info across WireRef.
This guide provides practical interpretation of NEC requirements. Always verify with your local AHJ and the current NEC edition adopted in your jurisdiction. WireRef is a reference tool and does not replace licensed professional judgment.

NEC references verified May 2026