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An isolated ground (IG) is a local ground connection used with a supply, one of the common earthing arrangements used with domestic mains supplies.
The primary reason for the use of isolated grounds (IG) is to provide a noise-free ground return, separate from the equipment grounding (EG) return. The EG circuit includes all of the metal conduit, outlet boxes, and metal enclosures that contain the wiring and must be grounded to provide a safe return path in case of fault currents. The IG' provides an insulated, separate ground path for the ground reference in electronic equipment, such as computers, hospital equipment, and audio equipment. IG helps eliminate the potential for a ground loop, which can cause noise, data errors, and disruptions to these systems. The IG is typically insulated and separate all the way back to the point of origin of the circuit, either a main panel or sub-panel. The IG, EG and neutral are all bonded together at that point. Due to the installation of a separate, insulated conductor and the associated special outlets required, IG circuits are more expensive to install than standard power circuits.
Its main downside is its usually higher impedance than other earthing systems, resulting in slightly lower safety levels.
Until the 1950s, isolated ground domestic mains supplies tended to have no RCD or ELCB, and too high a ground impedance to blow a fuse if a live to earth fault occurred. This could leave metalwork in the house live. The use of RCDs (or formerly ELCBs) with such installs solved this problem. Such installs are called EEBAD (Earthed Equipotential Bonding and Automatic Disconnection).
The British term for isolated ground is "IT", from the French terre isolée.
An isolated ground, if installed correctly, can reduce some electrical noise. However, complete power conditioning and protection will usually require other devices such as a surge protector or an uninterruptible power supply. If the receptacle is not installed correctly, it can create a dangerous installation.
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