UFC 3 -520-01
June 10, 2002
GROUNDING, BONDING, AND LIGHTNING PROTECTION
The term ground refers to the earth, or a large body that serves in place of the
earth. The term grounded refers to a system in which one of the elements is purposely
connected to ground. The term grounding refers to the process of establishing a
grounded system. Grounding is co mmonly performed incorrectly and poor grounding is
the principal cause of power quality problems.
The electric interconnection of conductive parts to maintain a common electric
potential is referred to as bonding.
In the context of this manual, lightning protection consists of the facility
design features intended to withstand direct lightning strikes and then channel the
lightning surge to ground.
The term surge refers to a voltage or current transient wave, typically lasting
less than a few milliseconds. Protection against surges is referred to as surge
protection. Chapter 11 provides surge protection design criteria.
NEC GROUNDING AND BONDING REQUIREMENTS .
Electrical systems and circuit conductors are ground ed to limit voltages during
lightning and to facilitate overcurrent device operation in case of a ground fault. NEC
Article 250 (2002 Edition) allows the system neutral to be grounded and limits the
location of this neutral to earth connection to the sour ce side of the service entrance
disconnect or at a separately derived system.
For the Army and Navy, refer to NEC criteria for grounding and bonding
For the Air Force, refer to Air Force Instruction (AFI) 32-1065, Grounding
, for grounding and bonding requirements.
STATIC PROTECTION .
A static ground is a connection between a piece of equipment and earth to
drain off static electricity charges before they reach a sparking potential. Figure 10-1
shows a n example of static protection. Typically, static grounding involves connecting
large metal objects such as fuel tanks or an aircraft to earth through a ground rod.
Static grounds are not part of a n electrical power system, but if an equipment grounding
conductor is adequate for power circuits, it is also adequate for static grounding.