Principals Of Electrical Grounding

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Principles of Electrical  Grounding   By:      John C. Pfeiffer, P.E.     Pfeiffer Engineering Co., Inc.

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Abstract:
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This is a discussion of the basic principles behind grounding systems and how grounding is
/ ^6 t% T, H5 s+ O, L+ D: e0 Zrelated to safety and the effective operation of circuit protection devices such as fuses and circuit
breakers. The discussion moves quickly from a basic study of grounding to simple examples of a
single building installation and onto facilities with multiple buildings and structures. Finally the
8 {9 Y1 J' d: x0 E$ {: Vdiscussion will briefly cover grounding as it applies to lightning protection and the control of
' T1 o9 ^3 B& Sstatic electricity.
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introduction:
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! Q' J( U- o8 Y$ X" \& A6 @Grounding to most engineers, technicians and electricians is a simple subject and little attention
is paid to it other than knowing that something is required. To some people there are grounds and
+ i6 O  J( I: G5 bthen there are “Clean Grounds”. Thirty years ago when computers were relatively new, there
were many approaches to grounding, particularly for electronics and computers. Some of these
' P0 \& t6 s6 R" A; p* `2 Z0 j9 xapproaches established what was called a “Clean Ground” which was often isolated from the
power grounds.
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Many of these ideas have been proven to be ineffective and sometimes dangerous to equipment
5 q6 Y, A5 S) @" oand personnel. As frequencies became higher and higher (computer speeds faster and faster)
1 b' z2 p1 M* p  [! y+ V/ bresearch accelerated into the subject of grounding, shielding, EMI, lightning protection and static
/ i8 }: ^$ e6 |electricity. The research resulted in the basic science behind grounding. This subject is not as
simple as once thought and one needs a clear understanding of the basic principles.

4 K6 J# U, M( I: H# EFirst, the ground or grounding of a circuit is a misnomer. For most purposes the term means
earthing or connecting the circuit to earth. In actuality, it=s connecting the circuit to a common
5 R6 N  ~0 S9 f3 ^/ g& k4 g, Cpoint of reference; for most systems that is the earth.

$ W9 e( y4 r; G& z6 OGrounding=s main purpose is to provide a common point of reference between various sources of
4 @5 l: O/ M: l8 O( eelectrical energy, i.e.
         Different power systems            - Public Utilities, on-site generation, battery systems
         Different voltage systems          - 138,000v, 13,800v, 480v, 120v, etc.
) N+ y0 {  X5 L) r         Different energy sources           - Electrical Energy, Lightning, Static Electricity, RF
/ R8 I, p9 \2 K5 |* W0 K2 N' a         Energy
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* M" b, b; l+ q+ V/ x0 d9 J5 ]In any discussion of the grounding of electrical systems, particularly as it applies to power
! P- c( v4 [) r+ ^9 fsystems, there also needs to be a consideration of how the grounding system relates to
overcurrent protection. They go hand in hand.

+ k. o- t9 `2 b0 e# N! f7 m4 DThere are also a number of misconceptions that affect how a ground system works. The
following facts are generally not known or are misunderstood.
         The earth is NOT always a good ground.
         What is acceptable at 60 Hz does not always work at high frequencies.
         The interconnection of systems with even large conductors may be ineffective when

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