IGR

Isolated Ground Receptacle. Often used in premises wiring intended for audio and/or computer systems. Usually orange, or denoted with an orange triangle (when of NEMA 5-15/20 type).
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http://www.iaei.org/magazine/2006/0...-circuits-got-clean-grounds-or-dirty-grounds/

For more, see http://ecmweb.com/content/basics-isolated-grounding-receptacles .
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