Ground     Electrical ground in an AC power system is a wire that is connected to the earth, hence the name "ground". The reason for such connection stems from the need to protect users of electrical equipment from shock hazards. Power is delivered to the utilization site using a pole mounted or other type of transformer. The output of such a transformer consists essentially of two lead wires, with the utilization voltage available between the leads. For a variety of complicated reasons involving safety, one of these transformer lead wires is connected to the earth using a copper bar driven into the ground. From this ground connection, two wires are taken to the power utilization point. One of these wires is called the "safety ground" or "green" wire and the other is called the "neutral" wire. The ungrounded lead from the transformer is also taken to the utilization point and is called the "hot" wire. These three wires together (hot, neutral, and safety ground) make up the connections found on a typical office power receptacle. The safety ground wire appears to be redundant since the neutral wire is derived from the same point. In fact the safety ground wire isn't needed as evidenced by the large number of electrical appliances which only use only two (hot and neutral) prongs. In electrical equipment which has a safety ground connection (as evidenced by a three prong plug), the safety ground is always connected to any exposed metal parts of the equipment. The purpose of this connection is to prevent any exposed part of the equipment to become energized with a hazardous voltage in case of a wiring fault inside the equipment. In computer equipment, computing circuits and mainboards are electrically connected to the chassis and therefore to the safety grounding wire.

Ground Loop     An unintentionally induced feedback loop caused by two or more circuits sharing a common electrical ground.

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