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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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Don’t SWER No More
A very, very long time ago, telegraph systems were based on just one copper wire laid down over several miles. Metal poles buried in the ground on both sides completed the return path of the current (through moist subsoil, water, sea, or even ocean). This is called for single-wire earth return (SWER). This single-conductor principle was used extensively in power distribution systems even later, and is still considered an effective and economical choice for rural electrification in remote and backward locations. The same single-conductor principle is also often used today for modern light-rail systems, remote water pumps, and so on.
Unfortunately, completing a return path through (earth) ground creates a current loop with ...

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