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Regardless of size, all enclosures will emulate, or assume, the voltage of the Earth. They will act as electrical copies, or mirrors, of the Earth, albeit as miniatures. Because the Earth has so much change in voltages and current flow, electrical copies within a facility may not be able to keep up with all the changes. This means that the electrical copies can become false, and present an opportunity for flashover among different enclosures.
What is supposed to happen is that as the earth's voltage changes, it should immediately change at the GES by simply flowing onto, or away from, the GES. Thus, changes and pooling of voltage behave rather like tidal pools and tidal waves. In turn, this process of balancing voltage and current flow repeats between many pairs of points, each representing a point of failure or damage requiring periodic inspection and maintenance.
What is not supposed to happen is an improperly grounded neutral conductor and weak or missing grounding connections. These prolong the refreshing of electrical copies and create the hazard of a person or animal becoming an unwilling connection that re-establishes ground or balances the current flow. If the potential difference between points and / or surfaces is great enough, then flashover can occur at any time.
Bonding multiple indoor ISBPs also creates an electrical copy of an outdoor ISBP when all services become integrated.
Obviously, an outdoors ISBP is preferred over the indoor version, because flashover is kept out of the occupancy. As an authoritative guide for electrical and fire safety, the NEC promotes the preference for outdoor versions of the ISBP for this reason. But the achievement of an electrical copy indoors is about the best you can do under the circumstances when an outdoors ISBP is not available or practical to create. NIST Special Publication 960-6 introduces the concept of indoor ISBPs dedicated to protecting individual devices such as computers and high value appliances and consumer electronics by bringing indoors fresh electrical copies.
Enclosures behave electrically as the Earth does, making them electrical copies. Electrical copies have specific points of failure that can be monitored and periodically maintained, repaired, and upgraded.
The danger with electrical copies is that they may not keep up with the Earth's changes, and therefore invite flashover or present an electrocution hazard at or near the occupants at a served facility. An improperly grounded neutral conductor and weak or missing grounding connections are two examples of such points of failure.
The ISB Project seeks to control this process of changing currents by providing sufficient bonding and grounding to control flashover and to aid the refreshing of electrical copies, whether indoors or out.
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