GFCI - History, Purpose and How They Work (9-14-99)

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The U.S. Consumer Product Safety Commission (CPSC) recommends the use of a ground-fault circuit- interrupter (GFCI) with every power tool to protect against electrical shock hazards. Each year, CPSC learns of approximately 20 to 30 electrocution deaths associated with power drills, saws, sanders, hedge trimmers, and other electric power tools. Most of these deaths could be prevented by the use of a GFCI.

What is a GFCI? A GFCI constantly monitors current flowing in a circuit to sense any loss of current. If the current flowing through two circuit conductors differs by a very small amount, the GFCI instantly interrupts the current flow to prevent a lethal amount of electricity from reaching the consumer. The consumer may feel a painful shock but will not be electrocuted. GFCIs are the most effective means for protecting consumers against electrical shock hazards.

  1. To understand (graphics) more on how a GFCI works,
  2. see

  3. For the National Electrical Code GFCI protection requirements (history),


From Wescoatt, Mike <>

A book that has become a sort of GFCI bible to us in our workplace and training is "Overcurrents and Undercurrents" by Earl W Roberts, Mystic Publications, 10 Mason's Island Road, CT, 1996, 860.536.2616. This book has allowed us to use Ground Fault Circuit Interrupters (GFCI) devices in the best way possible in our wet theatrical/pool/commercial/industrial/special applications environment that we work in that the NEC has not covered in some cases. This book has allowed us to see the theory behind GFCI devices and adopt rules and regulations that lead to the safest environment possible for our technicians, artists, scuba divers, and the general public.