Section 250.50/Grounding Electrode System
NEC 250.50 requires all grounding electrodes at a building to be bonded together to form the grounding electrode system.
All grounding electrodes present at a building must be bonded together to form the grounding electrode system. Required electrodes include: metal underground water pipe in contact with earth for at least 10 feet, metal building frame effectively grounded, concrete- encased electrode (Ufer ground: 20 feet of bare copper in concrete footings), and ground ring. If none of these are present, made electrodes (ground rods, ground plates) must be installed. Two ground rods must be at least 6 feet apart unless one rod achieves 25 ohms or less resistance to ground.
Why this section exists
The grounding electrode system provides the connection between the electrical system and the earth. This connection limits the voltage imposed by lightning, line surges, and unintentional contact with higher-voltage systems. Bonding all electrodes together creates the lowest possible ground resistance and ensures equipotential across the building. A single ground rod in dry soil may have a resistance of 100 ohms or more, while a concrete-encased electrode in a building footing typically achieves 5 ohms or less.
What plan reviewers look for
Plan reviewers check the electrical site plan and grounding details for the grounding electrode system. They verify that all available electrodes are bonded together with properly sized grounding electrode conductors per Table 250.66. They check for the concrete-encased electrode (Ufer ground) in the foundation plan. They verify ground rod locations and separation distance on the site plan.
Common violations
Related NEC requirements
Section 250.52 lists the types of grounding electrodes. Section 250.53 covers electrode installation requirements. Section 250.66 covers grounding electrode conductor sizing. Section 250.30 covers grounding of separately derived systems that connect to the electrode system.