Ground fault protection is not new, having been introduced in the 1971 edition of the National Electrical Code. GFCI devices have saved many lives since then by preventing shock and electrocution. As you may know, they contain a small transformer that detects current leakage from the phase to the grounded (neutral) conductor. That is why they work even in circuits that do not have a separate grounding conductor. These devices are designed to interrupt current when the leakage reaches a threshold of 4 to 6 mA, just shy of the amount of current that can cause injury to the human body.