Isolated-ground Receptacles
Take The Electromagnetic Noise Out Of Your Audio System
By Timothy Thiele, About.com Guide
Isolated-ground receptacles have their uses in today's home. They are used to provide power to and protect circuit feeds, like those that have sensitive electronic devices attached to them. Quite often, electromagnetic noise becomes a problem in a regular ground wire's system and this noise is transmitted though audio systems. This can also effect picture quality on television screens. Quite often this noise results in a humming or buzzing sound.
Wiring an isolated-ground receptacle isn't all that difficult. You'll need a three wire NM cable with a ground wire. The black wire connects to the brass-colored terminal, the white wire connects to the silver-colored terminal, the bare ground wire connects to the box ground screw, and the red wire will connect to the isolated-ground receptacle's ground screw. This ground screw is unlike those on other receptacles. What I mean is this ground screw is not physically connected to the grounding plate, only to the rounded ground holes of the two receptacle slots.
Now, don't forget to place some green phasing tape on the red wire at each end to indicate it is indeed a ground wire, not a hot wire. Wire color coding is important so that everyone that works on the circuitry has an idea of what each wire is being used for. Phasing the wire tells everyone that this wire is a ground wire and, since it is a converted red-colored wire, it likely has a special use.
Isolated-ground receptacles are orange-colored receptacles with special markings. If you look closely at the face, you'll notice a green triangle on it. This symbol indicates that the receptacle has an isolated ground.
In the electrical panel, the bare ground wire and the green-taped red wire both connect to the ground buss. Sometimes there will only be a neutral buss, but this is bonded to the case of the electrical panel. This allows the neutral and ground connection to be at the same potential, making this connection a combination neutral/ground connection. If at all possible though, a ground connection directly to the grounding buss, which is connected to a ground rod, is preferred. This special ground connection between the isolated-ground receptacle's ground connection and the electrical panel's grounding or neutral bus, provides a dedicated ground path for electricity to flow without electromagnetic interference.
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