Grounding

Grounding: The Key To Lightning Protection

Properly made ground connections are essential to the effective functioning of a lightning protection system, as they serve to distribute lightning into earth ground. You can say that grounding is The Key To Lightning Protection. A grounding system typically includes a copper-bonded ground rod that is installed in the ground. When installing lightning protection, ground electrodes should be at least one-half inch in diameter by eight feet long. Copper-clad electrodes are recommended. In most cases a lightning protection system will have a minimum of two ground rods with an additional ground rod added for each 100 ft of a structure.

Counterpoise or Ground Loop Grounding

The most effective systems consist of an extensive conductor network buried surrounding the building to which the down conductors are connected. This system is called a Counterpoise Grounding System and often referred to as a “ground loop”. A ground loop encircling a structure interconnecting all downlead cables at their base and/or grounding electrode devices is the best way to equalize potential for an entire lightning protection system. It is always possible to have varying resistance values for grounding electrodes even on the same structure.

Since splitting the lightning along multiple paths begins at the strike termination point and follows through the conductor system to ground, different resistance values of electrodes can upset this function. An in-ground loop solves this potential problem and provides an extensive wire network to enhance the grounding system. A ground loop is required for every structure exceeding 60 feet in height. If an interconnecting loop cannot be installed in the earth, then it may be placed within the construction to fulfill this requirement. This ground level loop also accommodates connection with other building grounded systems.

Triangulated Delta Grounding

Where space is limited a triangulated delta system may be used to help dissipate energy in the ground. In this system ground rods are coupled and driven into the earth until the desired resistance is achieved. A conductor is then exothermically welded to the rods to interconnect the series of rods.

All grounding media in or on a structure shall be interconnected to provide a common ground potential using main size lightning conductor. This includes the lightning protection grounding electrode system, electric, communication, and antenna system grounds along with metallic piping systems entering the structure like water, gas and LPG lines, metal conduits, etc. Interconnection to gas lines shall be made on the customer side of the meter to avoid defeating any cathodic protection of service lines. Where all these systems are bonded to a continuous metallic water line system, only one connection is required between the lightning protection grounding and the water line. System interconnection may be made at multiple points near structure entrances for systems, or one hard connection at a ground bar may be used. Bringing all building grounded systems to the same potential at grade is the first step toward protecting internal components and people from lightning. It begins the bonding process against side flashes from system components to internal building systems.

Static Grounding

Airports require special attention to grounding. They not only handle fuel in close proximity to masses of people, but the airport is usually on high ground and therefore subject to lightning strikes. Static grounding is required whenever an airplane is refueled. This is normally accomplished by positioning a properly installed static grounding receptacle in the tarmac near the location where the refueling takes place.

A static ground lead is attached to this receptacle from both the refueling vehicle and from the aircraft before the fuel hoses are attached to the aircraft. This equalizes any potential difference between the two vehicles preventing a static spark.

Static grounding receptacles are installed flush with the finished tarmac. The receptacle is welded to either a ground rod or ground grid or both. Receptacles that screw onto a threaded (sectional) rod are also available but the threaded connection may increase in resistance with time.

Static grounding receptacles have an internally cast ball (also available with a removable ball) for attaching the grounding clamp and are supplied with an attached cover. Static grounding receptacles can be welded directly to a ground rod. A ground conductor can be welded to the static grounding receptacle at the same time the receptacle is welded to a ground rod.

Lightning protection also should be installed on the airport structures.