Hubbell Wiring Device.pdf - Eversave Technology

SpikeShield ® Power Quality ProductsIsolated Ground StoryHubbell Isolated Ground ReceptaclesWhy do you need an isolated ground device?When mounting a conventional receptacle in a steel box, the groundis commonly established through the existing electrical system. Thisis done by using either the grounding clip on the receptacle’smounting strap, or by running a ground wire (which is part of the“normal” existing system) to the green grounding screw.In a conventional receptacle the grounding contacts are connected tothe mounting strap and the green grounding screw. Thus, even whena separate green wire is brought to the receptacle, it is still tied intothe normal ground. This occurs since the mounting strap is in contactwith the box grounding system, therefore, a “pure” isolated path to theground is not established.The ProblemThe conventional grounding receptacle provides safety for personneland equipment. However, the ground network also serves as a giantantenna and conductor of electrical noise. This electrical noise iselectromagnetic interference and is caused by numerous transientground currents. This can produce random transient electrical signalson the grounding system.As a result, sensitive electronic equipment such as point of purchaseterminals, accounting machines, computers and highly sensitivemedical and communications equipment, can pick up these transientsignals. This can interfere with the proper operation of the equipment.The SolutionThe isolated ground receptacle is similar to a conventional receptacleexcept for one important change. Insulating barrier construction, firstpatented by Hubbell, isolates the ground contacts from the mountingstrap. The green grounding screw is connected directly to the groundingcontacts. The isolated equipment grounding circuit is completed byrunning an isolated ground wire to the green grounding screw. Thisground wire passes through intermediate panel boards without beingconnected to their grounding terminal and terminates directly at anequipment grounding conductor terminal of the derived system orservice, in accordance with NEC ® requirements.The ResultThis “isolated ground” can be kept relatively free of electrical noise.This is achieved since the grounding network has less branches, fewersources of noise, and is connected to the ground at a single point.Green Hex HeadGrounding Screwand CircuitConduitNormal "Common"Building GroundInsulatingBarrierGreen Hex HeadGrounding Screwand CircuitConduitNormal "Common"Building GroundDerived Systemor Service GroundConventionalReceptacleIsolated GroundReceptacleMounting StrapBondingJumperOutletBoxMounting StrapOutletBoxIsolatedGroundSpikeShield ® Power Quality Products Isolated Ground StoryDimensions in Inches (mm)www.hubbell-wiring.comJ-19