This publication is a guide of practical information containing instructions for the safe and proper application of ground fault protective devices (hereafter referred to as GFP devices).

GFP devices include current sensing devices (GFS), relaying equipment (GFR), or combinations of current sensing devices and relaying equipment, or other equivalent protective equipment which will operate to cause a disconnecting means to open all ungrounded conductors at predetermined values of ground fault current and time. GFP devices are intended only to protect equipment against extensive damage from ground faults.

GFP devices are intended to operate circuit breakers or fusible switches equipped with electrically actuated tripping means. These devices may be supplied as an integral portion of the disconnecting means or as separate devices operating in conjunction with the disconnecting means. GFP devices may or may not require external control power for proper tripping operation.

GFP devices are designed to be used primarily on solidly grounded distribution systems rated up to a maximum of 1000 V AC to provide for rapid clearing of ground faults. The National Electrical Code requires ground fault protection in certain instances. In other situations, ground fault protection is added at the request of the customer. This application guide does not cover all possible applications of these devices.

Ground fault protection systems described in this publication are intended for equipment protection only. They cannot provide protection for personnel. A ground fault relaying system designed for protecting equipment cannot protect personnel against electric shock hazards because personnel protective devices, such as ground-fault circuit-interrupters, require a sensitivity in the low milliamp range. The systems used to meet the requirements of Article 230-Services and Article 517-Health Care Facilities of the National Electrical Code have a sensitivity in the multi-amp range. This application guide does not contain information on ground fault protection for personnel (GFCI).

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