The term grounding electrode, as defined in Article 100, refers to conductive objects. The definition also describes the primary function of a grounding electrode. An important feature is that the electrode is in direct contact with the earth, making a connection. This means that the electrode is acceptable and performing as a grounding electrode without being connected to a wire. 

It is clear from this definition that a grounding electrode makes and maintains the connection to ground. A ground rod is not a grounding electrode until it is driven into the earth to complete the connection. A metal water pipe is not a grounding electrode unless at least 10 feet of the piping is in direct contact with the earth. 

Note that no depth is required for the water pipe, but historically, the water pipe electrodes were buried at least 24 inches deep because of local water service company installation regulations. The National Electrical Code does not distinguish between underground water piping that is outside or inside a building perimeter. The same concept of direct connection to the earth is found for all grounding electrodes covered by 250.52(A).

What’s the purpose?

A grounding electrode’s purpose is to function as the connection between grounded electrical systems and equipment and the earth. The NEC does not provide details about the effectiveness or resistance of a grounding electrode or grounding electrode system, other than for a single rod, pipe or plate electrode. The NEC also does not address long-life or end-of-life expectancies for grounding electrodes.

From an NEC standpoint, grounding electrode performance is essential if electrical services and systems are energized. The earth is a conductor, but its conductivity is variable and affected by nature. The connection to the earth is usually better when the ground is moist or wet and tends to be less effective in dry or rocky soil. The resistance between the earth and a grounding electrode varies depending on geographical location, seasonal conditions, the soil’s mineral content and earth temperatures. 

If more than a single grounding electrode is installed and used, the NEC treats it as a grounding electrode system. Multiple grounding electrodes that form a system benefit from multiple earth connection characteristics and locations for the same building or structure. It is reasonable to conclude that a system of multiple grounding electrodes should perform better than a single grounding electrode due to the multiple connections to earth. This is a reason why grounding electrodes at each building or structure served must be interconnected to perform as a system of electrodes for the life of the building or structure. 

Maintaining the connection

Remember that the grounding electrode establishes and maintains a connection to the earth. It has little to no effect in facilitating overcurrent protective device operation. The earth is never suitable as an effective ground-fault current path. Many have erroneously insisted that the earth is necessary in the safety system to cause overcurrent protective devices to open in ground-fault conditions, but the earth is not to be used as a path for normal current or as an effective ground-fault current path to carry any level of fault current necessary to cause circuit breakers or fuses to operate. 

The NEC provides rules in Part III of Article 250 indicating which electrodes are required to be used for grounding electrode systems. These are not optional. The first sentence of 250.50 outlines the general requirement that all electrodes present at a building or structure be used to form a grounding electrode system. This section addresses each building or structure served by electrical power. If a building or structure has no electrical system, there is no NEC requirement for a grounding electrode. A network of grounding electrodes for a lightning protection system may be installed on a structure not supplied by an electrical power service or system, such as a barn or shed.

The grounding electrodes addressed in 250.52(A) include those inherent to building construction and electrodes that must be installed. Examples of installed grounding electrodes include ground rods, plates, ground rings and chemically enhanced electrodes. 

On the other hand, concrete footings and foundations, metal in-ground support structures, metallic underground water pipes and local underground conductive systems or structures are examples of grounding electrodes inherent to many types of building construction. The NEC is clear that if grounding electrodes are present, they must all be used (bonded together) to form the grounding electrode system and connected to the power or service supplying that building or structure.