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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8 m$ b2 B- R6 D% BAbstract:
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- Z8 r: C" l( r: K, e& mThis is a discussion of the basic principles behind grounding systems and how grounding is
# [' B% r* }6 H% Y6 ~7 grelated 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
$ b2 |9 E8 n1 Z8 r" U3 D9 ?discussion will briefly cover grounding as it applies to lightning protection and the control of
# ~2 E$ y9 ?* g* p7 j8 o  ?static electricity.
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introduction:
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, @% T$ U% j& k( i6 j; e% TGrounding 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
0 t5 m4 q! j6 r0 g) b/ Dthen there are “Clean Grounds”. Thirty years ago when computers were relatively new, there
; V. A: ]2 h" Q. \were many approaches to grounding, particularly for electronics and computers. Some of these
approaches established what was called a “Clean Ground” which was often isolated from the
power grounds.

( B; \% E6 w. @Many of these ideas have been proven to be ineffective and sometimes dangerous to equipment
and personnel. As frequencies became higher and higher (computer speeds faster and faster)
5 y* l& @8 J1 R4 N( h7 wresearch accelerated into the subject of grounding, shielding, EMI, lightning protection and static
7 v! O8 R2 [( r6 l, C2 j% ?/ Welectricity. The research resulted in the basic science behind grounding. This subject is not as
1 m% c. D4 K4 U& g  K8 H1 c  Isimple as once thought and one needs a clear understanding of the basic principles.
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First, the ground or grounding of a circuit is a misnomer. For most purposes the term means
! c2 ~( z$ P* P2 }; Z5 ?1 Eearthing or connecting the circuit to earth. In actuality, it=s connecting the circuit to a common
point of reference; for most systems that is the earth.
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4 M5 \8 p) l" ?* o9 PGrounding=s main purpose is to provide a common point of reference between various sources of
electrical energy, i.e.
         Different power systems            - Public Utilities, on-site generation, battery systems
1 N# t! g9 d6 Y$ D1 {, `         Different voltage systems          - 138,000v, 13,800v, 480v, 120v, etc.
4 U9 P( V5 e4 h4 `/ j+ C$ q' x3 H         Different energy sources           - Electrical Energy, Lightning, Static Electricity, RF
$ ~3 l' t2 c  m# f1 f         Energy
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) y. ?0 \/ B9 s7 ?# x1 D: ]) ^1 QIn any discussion of the grounding of electrical systems, particularly as it applies to power
systems, there also needs to be a consideration of how the grounding system relates to
; v. ~' e1 A! W) a4 I+ Xovercurrent protection. They go hand in hand.

$ i! c* x8 I; v4 hThere are also a number of misconceptions that affect how a ground system works. The
following facts are generally not known or are misunderstood.
' @+ _+ D1 e1 p' j+ S7 K, s         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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