Dual trip level ground fault interrupter

Abstract

A dual trip level ground fault interrupter (GFI) which is designed to trip or operate at a first relatively low personnel protection level of ground leakage current, and also at a second relatively high equipment protection level of grounded leakage current. The dual trip level ground fault interrupter is provided for a power line, having line conductors and a ground conductor, supplying electrical power to a load. The dual trip level GFI comprises first and second differential current transformers, each having a primary winding and a secondary winding. All of the line conductors for the load pass through the primary winding of the first differential current transformer. All of the line conductors and the ground conductor pass through the primary winding of the second differential transformer. The ground conductor does not pass through the primary winding of the first differential current transformer. The first differential current transformer responds to the total ground leakage current, and is wound to achieve a trip voltage at a high equipment protection level of ground leakage current (e.g. 30 ma). The second differential current transformer responds to any leakage current not returning on the ground conductor, and is wound to achieve trip voltage at a lower personnel protection level of ground leakage (e.g. 5 ma).