How is the grounding electrode conductor sized?

The grounding electrode conductor is sized from NEC Table 250.66 based on the largest ungrounded service-entrance conductor. For example a 2/0 copper service conductor requires a 4 AWG copper grounding electrode conductor. A connection to a ground rod only never needs to be larger than 6 AWG copper.

Why is a concrete-encased electrode required when available?

NEC 250.50 requires that all grounding electrodes present at a building be bonded together. A concrete-encased electrode, sometimes called a Ufer ground, is one of the most effective electrodes, and if it exists in the foundation footing it must be used and bonded into the system.

What is the difference between the main service and a subpanel?

At the main service the grounded neutral and the equipment ground are bonded together through the main bonding jumper. At a subpanel they must be kept separate, with an isolated neutral bus and a separate equipment ground bus, and the feeder must include an equipment grounding conductor. The checklist changes accordingly.

Does metal water piping need bonding?

Yes. NEC 250.104 requires interior metal water piping likely to become energized to be bonded to the service equipment, the grounded conductor or the grounding electrode system, sized per Table 250.66. If the metal water pipe is also in contact with earth for at least ten feet it additionally serves as a grounding electrode.

Do two ground rods always need each other?

A single made electrode such as a ground rod that does not have a resistance to earth of 25 ohms or less must be supplemented by a second electrode per NEC 250.53(A)(2). In practice most installers simply drive two rods at least six feet apart by default to satisfy this without testing resistance.

What is the Grounding & Bonding Checklist Generator (NEC 250)?

Builds a printable NEC Article 250 grounding and bonding checklist from service amperage, panel type, electrode types and the presence of metal water piping and structural steel, sizing the grounding electrode conductor and equipment bonding jumper from Tables 250.66 and 250.102. Runs in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Grounding & Bonding Checklist Generator (NEC 250)

Name: Grounding & Bonding Checklist Generator (NEC 250)
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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NEC Article 250 governs how a service is grounded and bonded, and inspectors check it closely. This generator turns your service details into a printable checklist of the specific connections required, with the grounding electrode conductor and bonding jumpers sized straight from the NEC tables.

How it works

Two NEC tables drive the conductor sizing. The grounding electrode conductor comes from Table 250.66 indexed by the largest ungrounded service conductor, and equipment bonding jumpers come from the same table for the supply side. The tool applies these rules:

GEC size       ← Table 250.66 (by largest service conductor)
to ground rods ← never larger than 6 AWG copper (250.66(A))
main bonding   ← main service only; subpanels keep neutral and ground separate
electrodes     ← all present electrodes must be bonded together (250.50)

Based on the panel type it includes either a main bonding jumper (service) or separated neutral and ground buses plus a feeder equipment grounding conductor (subpanel), then lists every electrode and bonding connection you have to make.

Worked example: 200 A residential service

Consider a typical single-family home with a 200 A main panel, 2/0 AWG copper service-entrance conductors, a pair of ground rods, a metal water pipe entering from the street, and a poured concrete foundation:

Item	Rule	Sizing / requirement
Grounding electrode conductor (GEC)	Table 250.66	4 AWG copper (for 2/0 service)
GEC tap to each ground rod	NEC 250.66(A)	6 AWG copper maximum
Ground rods	NEC 250.53(A)(2)	Two rods at least 6 ft apart if not 25 Ω
Metal water pipe bond	NEC 250.104	4 AWG copper (same as GEC)
Concrete-encased electrode	NEC 250.52(A)(3)	Must be used if present, 20 ft of 1/2-in rebar or 2 AWG wire
Main bonding jumper	NEC 250.28	Required at main service; remove at subpanel

All electrodes — rods, water pipe, and the Ufer ground — must be bonded together into a single grounding electrode system per NEC 250.50.

Service vs. subpanel: the critical difference

At the main service the grounded neutral and the equipment ground share the same bus through the main bonding jumper. At a subpanel (any panel fed from another panel) these must be kept entirely separate: the neutral bus is isolated from the enclosure, a separate ground bus bonds to the enclosure, and the feeder must carry a fourth wire — the equipment grounding conductor — back to the main panel. Leaving the neutral and ground bonded at a subpanel creates parallel neutral return paths, a shock hazard and a code violation.

Common inspection failures

Ground rods driven fewer than 8 ft deep (NEC 250.53(B) requires full 8 ft unless rock is encountered).
Metal water pipe bond run to the wrong side of the water meter — it must be to the street side, or both sides must be bonded.
Forgetting the intersystem bonding termination (NEC 250.94) for cable TV, telephone and solar system grounds.
Subpanel neutral and ground tied on the same bar — the most common subpanel deficiency on inspection.

Always confirm conductor sizing and electrode requirements against the specific NEC edition adopted by your local authority having jurisdiction, as some jurisdictions amend Article 250.