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A Faraday cage is a metallic enclosure that prevents the entry or escape of an
electromagnetic field. An ideal Faraday cage consists of an unbroken, perfectly
conducting box. This ideal cannot be achieved in practice, but can be
approached by using channels, grooves, and conductive material to seal any
openings. Contrary to popular belief, it does not need to be connected to ground
for the Faraday cage to be effective.
Faraday cages are used in electronic labs where stray EM(Electro-Magnetic)
fields must be isolated from penetrating the cage. This is important in the testing
of sensitive wireless receiving equipment.
A heavy-duty Faraday cage can protect anything inside against direct lightning
strikes. When properly connected to an earth ground, the cage conducts the high
current harmlessly to ground, and keeps the EM pulse from affecting personnel
or hardware inside.