ERICO Practical Guide to Electrical Grounding - Manual (Page 5)

WHY DO WE NEED ANOTHER
BOOK ON GROUNDING?
This book is designed for the contractor who finds that
installing grounding systems, which are in compliance with
all relevant codes and standards, is a complex and
somewhat mystifying assignment. While in larger facilities,
the design of a proper grounding system is certainly
complex and should be left to a qualified engineer, the
everyday grounding installations and applications covered
in this text are well within the scope of the qualified
contractor. In most facilities, a thoughtful contractor can
follow the guidelines and techniques in this book and be
reasonably ensured that he has done a competent and code
compliant job. This book is not written for the casual
contractor who was in the painting business last week. It is
for the electrical contractor who intends to be in business
next week, next year, and in the years to come. Design and
installation of electrical grounding systems is one of the
most important aspects of any electrical distribution
system, yet it is all too often misunderstood and
subsequently installed improperly. Some detailed
knowledge of the facility is needed, and the contractor who
intends to do the job correctly must make the investment in
time and tools - or hire someone to do these things for him.
Guesswork won’t do! The subject is too serious and
complex for that kind of approach. We hope you find our
recommended approaches helpful and cost-effective.
Article 250 of the National Electrical Code (NEC) contains
the general requirements for grounding and bonding of
electrical installations in residential, commercial and
industrial establishments. Many people often confuse or
intermix the terms grounding, earthing and bonding. To use
simple terms:
Grounding is connecting to a common point which is
connected back to the electrical source. It may or may not
be connected to earth. An example where it is not connected
to earth is the grounding of the electrical system inside an
airplane.
Earthing is a common term used outside the US and is the
connection of the equipment and facilities grounds to
Mother Earth. This is a must in a lightning protection system
since earth is one of the terminals in a lightning stroke.
Bonding is the permanent joining of metallic parts to form
an electrically conductive path that will ensure electrical
continuity and the capacity to conduct safely any current
likely to be imposed. A comprehensive review of grounding
and bonding requirements contained in the NEC appears in
Chapter 3 of this text.
NEC is a copyright of NFPA.
WHY GROUND?
There are several important reasons why a grounding
system should be installed. But the most important reason
is to protect people! Secondary reasons include protection
of structures and equipment from unintentional contact
with energized electrical lines. The grounding system must
ensure maximum safety from electrical system faults
and lightning.
A good grounding system must receive periodic inspection
and maintenance, if needed, to retain its effectiveness.
Continued or periodic maintenance is aided through
adequate design, choice of materials and proper installation
techniques to ensure that the grounding system resists
deterioration or inadvertent destruction. Therefore, minimal
repair is needed to retain effectiveness throughout the life of
the structure.
The grounding system serves three primary functions
which are listed below.
Personnel Safety. Personnel safety is provided by low
impedance grounding and bonding between metallic
equipment, chassis, piping, and other conductive objects so
that currents, due to faults or lightning, do not result in
voltages sufficient to cause a shock hazard. Proper
grounding facilitates the operation of the overcurrent
protective device protecting the circuit.
Equipment and Building Protection. Equipment and
building protection is provided by low impedance
grounding and bonding between electrical services,
protective devices, equipment and other conductive objects
so that faults or lightning currents do not result in hazardous
voltages within the building. Also, the proper operation of
overcurrent protective devices is frequently dependent upon
low impedance fault current paths.
Electrical Noise Reduction. Proper grounding aids in
electrical noise reduction and ensures:
1. The impedance between the signal ground points
throughout the building is minimized.
2. The voltage potentials between interconnected
equipment are minimized.
3. That the effects of electrical and magnetic field
coupling are minimized.
Another function of the grounding system is to provide a
reference for circuit conductors to stabilize their voltage to
ground during normal operation. The earth itself is not
Preface iii
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