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  • Cheater plug

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    A cheater plug, with metal grounding tab (lower right). The ground tab is designed to be attached to the outlet faceplate screw, which is supposed to be connected to the building electrical ground. A cheater plug, AC ground lifter or three-prong/two-prong adapter is an adapter that allows a NEMA 5-15P grounding-type plug (three prongs) to connect to a NEMA 1-15R non-grounding receptacle (two slots). They are needed to allow appliances with 3-wire power cords to plug into legacy ungrounded (two slot) receptacles found in older buildings. The use of such an adapter avoids the need to replace receptacles, but is potentially hazardous if the grounding tab is not connected to electrical ground. These adapters are illegal in some jurisdictions, in particular throughout Canada. A safer and more reliable alternative identified in the US and Canadian electrical codes is to replace the outlet with a Ground Fault Circuit Interrupter (GFCI) breaker outlet. Cheater plugs are also used to break ground loops in audio systems. This practice has been condemned as disregarding electrical safety.

  • Industrial and multiphase power plugs and sockets

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    Pin and sleeve connectorsIndustrial and multiphase plugs and sockets provide a connection to the electrical mains rated at higher voltages and currents than household plugs and sockets. They are generally used in polyphase systems, with high currents, or when protection from environmental hazards is required. Industrial outlets may have weatherproof covers, waterproofing sleeves, or may be interlocked with a switch to prevent accidental disconnection of an energized plug. Some types of connectors are approved for hazardous areas such as coal mines or petrochemical plants, where flammable gas may be present. Almost all three-phase power plugs have an earth (ground) connection, but may not have a neutral because three-phase loads such as motors do not need the neutral. Such plugs have only four prongs (earth, and the three phases). An example of a socket with neutral is the L21-30 (30 A) and the L21-20 (20 A) both of which have five pins (earth, neutral, and X, Y, Z phases). While some forms of power plugs and sockets are set by international standards, countries may have their own different standards and regulations.

  • Stray voltage

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    Stray voltage is the occurrence of electrical potential between two objects that ideally should not have any voltage difference between them. Small voltages often exist between two grounded objects in separate locations, due to normal current flow in the power system. Large voltages can appear on the enclosures of electrical equipment due to a fault in the electrical power system, such as a failure of insulation. A fallen power conductor from a transmission line forces current through the earth; the resistance of the earth to current produces a voltage difference between the point of contact and distant earth. If the rate of change of voltage with distance is large, a dangerous potential may exist between the feet of a person in the area.

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