The right hand figure illustrates an SPD connected between an incoming signal line, shown as a wire pair, and a piece of equipment. This is an improvement over the previous figure but it gives a relatively long path that introduces impedances and hence unwanted voltages to the protected equipment. There is still a large transient voltage developing between the ground point and the SPD, but this not appear across the equipment which receives only the limiting voltage of the SPD - which is as it should be. A typical installation includes a number of items of equipment or devices, each with its own connection. If these are all connected to a common point, from which a cable runs to ground, the result is a star-point earth system.
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The documents found in this Solutions area are extracted from in-depth surge protection Application Notes that are available for free download in the Departments area.