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Principles of Electrical Grounding John Pfeiffer, P.E. Abstract: This is a discussion of the basic principles behind grounding systems and how grounding is related to safety and the & 8230; & 8230; 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 discussion will briefly cover grounding as it applies to lightning & 8230;Implementation of good electrical grounding architecture is an & 8230; would dictate using large spacecraft design principles. Some of the example spacecraft use grounding & 8230;

Principles of Electrical Grounding John Pfeiffer, P.E. grounding. Grounding is, in essence, the control of abnormal voltages or currents through the proper application of Ohm=s Law: E = IR (Simplified Form) E = IR + jIX C + jIX L Grounding is the control or minimization of R in order to reduce the effects of E & 038; I. Improper grounding can cause more harm than no grounding. Misunderstood grounding often leads to the installation of improper grounding systems that are either ineffective, or even worse, dangerous. Electric Shock: An electrical shock (electrocution) occurs when two portions of a person=s body come in contact with electrical conductors of a circuit which is at different potentials, thus producing a potential difference across the body. The human body does have resistance and when the body is connected between two conductors at different potentials (voltage) a circuit is formed through the body and current will flow. When the human body comes in contact with only one conductor, a circuit is not formed and nothing happens. When the human body comes in contact with circuit conductors, no matter what the voltage is, there is a potential for harm. The higher the potential difference the more the damage. The effect of an electrical shock is a function of what parts of the body come in contact with each conductor, the resistance of each contact point, the surface resistance of the body at the contact, as well as other factors. When the electrical contact is such that the circuit path through the body is across the heart, you have the greatest potential for death. As shown in Figure 1, the human body=s resistance varies from as low as 500 ohms to as high as 600,000 ohms. As the skin becomes moist, the contact resistance drops. If the skin is moist, due to sweat that contains salt, the resistance drops further. Figure 1 illustrates the amount of current that can flow through the human body at three different potential differences across the body. Also shown is the effect of different current levels, both AC and DC. The ultimate effect is fibrillation, which causes the heart to stop, and results in death.

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