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Home / Code Guides / Grounding Electrodes

Grounding Electrode System — Ufer, Ground Rods & GEC Sizing

The grounding electrode system connects your electrical service to the earth itself — it stabilizes voltage and gives lightning and surges a path to ground. The NEC doesn’t let you pick just one electrode: every qualifying electrode present at the building must be bonded together into a single system, and new construction almost always means using the footing rebar.

RequirementModel Code StandardSection
All electrodes bondedEvery grounding electrode present at the building — footing rebar, metal water pipe, ground rods, building steel — must be bonded together to form one grounding electrode systemNEC 250.50
Concrete-encased electrode (Ufer)At least 20 feet of ½-inch rebar or 20 feet of bare 4 AWG copper encased in at least 2 inches of concrete in a footing in contact with earth qualifies — and where present in new construction, it must be usedNEC 250.52(A)(3), 250.50
Ground rods — the pair ruleA single rod is only sufficient if it measures 25 ohms or less to earth; since almost nobody performs the test, standard practice is driving two rods at least 6 feet apartNEC 250.53(A)(2), (A)(3)
Rod specificationsRod electrodes must be at least 8 feet long and driven to full depth (flush or below grade), with listed clamps rated for direct burialNEC 250.52(A)(5), 250.53(G), 250.70
Metal water pipeA metal underground water pipe with 10 feet or more in contact with earth is an electrode, but it can never be the only one — it must be supplemented by another electrodeNEC 250.52(A)(1), 250.53(D)(2)
GEC sizingThe grounding electrode conductor is sized from Table 250.66 based on the service conductors — but the portion running only to ground rods never needs to be larger than 6 AWG copper, and only to a Ufer never larger than 4 AWGNEC 250.66(A), (B), Table 250.66

Worth knowing

  • The Ufer electrode (named for the engineer who developed it in the 1940s) outperforms driven rods in nearly all soil — coordinate with the foundation contractor so a rebar stub or copper pigtail is left accessible before the pour.
  • A 200-amp residential service with copper service conductors typically needs a 4 AWG copper GEC to the water pipe or Ufer, but only 6 AWG to ground rods.
  • GEC connections must be accessible unless they’re exothermically welded, irreversibly crimped, or buried/encased with a listed fitting — a clamp hidden behind drywall fails inspection.
  • Don’t confuse grounding with bonding: interior metal water and gas piping gets bonded to the system, but bonding jumpers and the intersystem bonding termination (250.94) are separate requirements from the electrodes themselves.
Sections cite the 2021 International Residential Code and 2023 National Electrical Code as model standards. This is BuildSpec’s own summary — not ICC or NFPA text; read the authoritative language at codes.iccsafe.org. Your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.
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