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.

Grounding & Bonding Checklist Generator (NEC 250)

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.

Example and notes

A 200 A service with 2/0 copper conductors gets a 4 AWG copper grounding electrode conductor (Table 250.66), but the run to a pair of ground rods only needs 6 AWG. If a concrete-encased electrode exists it must be used; if metal water piping is present it must be bonded. At a subpanel, remove the main bonding jumper, isolate the neutral bus, and run a separate equipment grounding conductor with the feeder. Always confirm against the NEC edition adopted by your local authority having jurisdiction.