GROUND. The electrical connection to earth through an earth electrode
subsystem. This connection is extended throughout the facility via the
facility ground system, consisting of the signal reference subsystem, the
fault protection subsystem, and the lightning protection subsystem.
GROUND LOOP. Circulating common mode currents caused by DC, AC, Audio or RF
ground potential differences. Also referred to as Circulating Ground Currents
and Ground Current Loops.
GROUND PLANE. A conducting surface, plate or system of conductors used as a
common reference point for circuit signal current returns and electrical or
GROUNDING (GROUND). The process of providing a metallic surface with low
resistance or low impedance path to ground potential.
GROUND, SINGLE-POINT. A scheme of circuit/shield grounding in which each
circuit/shield has only one physical connection
to ground, ideally at the same point for a given subsystem. This technique
prevents return currents from flowing in the structure.
HAZARDOUS ELECTROMAGNETIC RADIATION TO FUEL (HERF). Potential for fuel and
petroleum products to be adversely affected by electromagnetic radiation.
HAZARDOUS ELECTROMAGNETIC RADIATION TO ORDNANCE (HERO). Potential for
munitions or electroexplosive devices to be adversely affected by
HAZARDOUS ELECTROMAGNETIC RADIATION TO PERSONNEL (HERP). Potential for
electromagnetic radiation to create a hazard for personnel.
HIGHER FREQUENCY GROUND. The interconnected metallic network intended to
serve as a common reference for currents and voltages at frequencies above 300
kHz and in some cases down to 30 kHz. Pulse and digital signals with rise and
fall times of less than 1 microsecond are classified as higher frequency
signals. High frequency in this sense should not be confused with the
broadcast HF band which covers from 3 to 30 MHz.
ISOLATION. Physical and electrical arrangement of the parts of an equipment,
system, or facility to prevent uncontrolled electrical contact within or
between the parts.
LIGHTNING PROTECTION SUBSYSTEM. This subsystem provides a non- destructive
path to ground for lightning energy and directs these high currents away from
susceptible elements and also limits the voltage gradients developed by the
high currents to safe levels.
LOWER FREQUENCY GROUND. A dedicated, single-point network intended to serve
as a reference for voltages and currents, whether signals, control or power,
from dc to 30 kHz and in some cases to 300 KHz. Pulse and digital signals
with rise and fall times greater than 1 microsecond are considered to be low
More than one path to ground.