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Lightning Surge Transmission Modes

January 14th Fact-of-the-Day

Most homes have three incoming power lines. One is grounded (usually at both ends). It connects to the center-tap of a secondary winding in a power transformer located on a nearby power pole in aerial transmission systems or inside a nearby ground-level cabinet in underground transmission systems. The other two lines connect to opposite ends of the secondary. Lightning may strike lines connected to either side of the primary, or both, to a line connected to either side of the secondary, or both, to the secondary ground line, the ground and either side, or any other combination. As a result, lighting surges may arrive in transmission mode, common-mode, on the ground line, or in any combination. The best protection against ground-line surges is a good home-side ground. Some surge protectors do not protect against all the other possibilities. Look for protectors designated both L-L (line-to-line) and L-G (line-to-ground). ©2005 Martek International All rights reserved.


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