Grounding Electrode Conductor - NEC Section 250 Definition

A Grounding electrode conductor (GEC) is a critical component in electrical systems, serving as the backbone of effective earthing practices. Understanding its role is essential for electrical engineering and maintenance professionals to ensure system safety, reliability, and compliance with the National Electrical Code (NEC). This ground (or earthing) conductor provides a direct path for fault currents to dissipate into the earth, reducing the risk of electrical surges and protecting both equipment and personnel. Proper implementation and sizing are not just regulatory requirements; they are vital for preventing failures, minimizing downtime, and ensuring the longevity of electrical installations in residential, commercial, and industrial settings.

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Conductor Sizing for Effective Earthing

The size of the grounding electrode conductor is crucial, and its determination often follows the guidelines outlined in Table 250.66 of the National Electrical Code (NEC). This table establishes the required conductor size based on the largest ungrounded service entrance conductor or equivalent area of parallel conductors. For example, systems with AWG copper conductors often require specific sizes to maintain effective current dissipation. Ensuring the correct size prevents overheating and provides an adequate fault current path, a critical safety feature in any electric service installation.

NEC Compliance and Safety Standards

Compliance with the NEC is non-negotiable in designing and implementing these systems. The NEC mandates that a grounding electrode conductor required must meet specific safety standards to protect against overvoltage conditions. By adhering to these regulations, electrical systems achieve consistency, ensuring that they function as intended and provide safety during fault conditions. The use of an overcurrent protective device adds another layer of security, safeguarding equipment and personnel from potential hazards.

The ultimate purpose of the grounding electrode conductor is to maintain safety by providing a low-resistance path to earth. This path is intended to carry fault current away from sensitive equipment, mitigating risks associated with electrical surges. It also protects the grounded conductor and ensures that connected equipment earthing conductors function correctly. A well-implemented system enhances the safety of an electrical installation, reducing the likelihood of catastrophic failures and ensuring a stable operation.

NEC requires that, where available on the premises at each building or structure served, all electrodes, including “made” electrodes, be bonded together to form the “Grounding Electrode System.”

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The “Grounding Electrode System” includes metal underground water pipes, metal frames of buildings, concrete-encased electrodes and ground rings.

The general requirement is that a bonding jumper must be installed between the grounding electrodes to bond them together.

• Grounding electrode conductor is run from the service equipment to one of the electrodes that are bonded together.
• NEC Section 250-24(c), is a requirement to connect the equipment conductors, the service-equipment enclosures, and where the system is grounded, the grounded service conductor to a electrode. The conductor used to make this connection is considered the “Grounding Electrode Conductor.”
• Grounding electrode conductor from an electrical service to a ground rod, pipe or plate electrode is never required to be larger than 6 AWG copper or 4 AWG aluminum unless the grounding electrode conductor continues on from the rod, pipe or plate to connect another electrode that may require a larger GEC such as a concrete encased electrode building steel or metal underground water pipe that qualifies as an earthing electrode.

The requirements of NEC Section 250.2 states that an effective ground fault current path is an intentionally constructed, permanent, low impedance, electrically conductive path designed and intended to carry current under a ground fault conditions from the point of a ground fault (like an overcurrent device) on a wiring system to the electrical supply source and that facilitated the operation of the overcurrent protective device. This is the function of a “Bonding Conductor” and not the function of a grounding electrode conductor.

With that assumption, and based on that incorrect interpretation, many electricians assume that in a properly functioning electrical system, currents in grounding electrode conductors are only present during faults, and only for a very short time.

Although further examination of 250.4 (A)(5) should make it clear that the earth shall not be considered an effective ground-fault current path, misconceptions still persist.

• Grounding electrode conductor from an electrical service to a ground rod, metal water pipe or plate is never required to be larger than 6 AWG copper.
• Aluminum grounding electrode conductors can not be in contact with earth, masonry or subjected to corrosive conditions.
• Grounding electrode conductor is permitted to “supply” or “serve” any number of electrodes, but must be sized for the largest grounding electrode conductor required.