This application guide covers ground fault circuit intermpiem (GFCI's) which are intended to provide electrical shock hazard protection from line-to-ground fault currents on grounded circuits of 120, 120D0, 240 volt single phase, 208Y/120 volt, and 240 volt three-phase; two, three, and four-wire supplies.

GFCi's are designated as Class A or Class B in accordance with UL Standard 943 (January 1985), Ground Fault Circuit Intempters.* Unless otherwise indicated, this application guide applies to class A GFCI'S.

Covered in this guide are characteristics of the various types of GFCI's, construction details, markhg data, installation guidelines, field testhg recommendations, and field troubleshooting information.

*Copies are available  from Underwriters Laboratories Inc., 333 Pfingsten Road, Northbrodt, IL 60062