Electronic – What’s the use of the ground socket of an ungrounded GFCI receptacle

circuit breakerfaultgroundingsafetyshort-circuit

Is the ground socket of a GFCI receptacle that isn’t connected to ground useful? (I'm in the United States, if it matters.) If the connected appliance had current on its ground pin, where would this current go in the ungrounded GFCI? If the current on the GFCI's hot and neutral are equal, including the case in which both are zero, will this ground-pin current cause the GFCI to trip and disconnect its internal hot, neutral, and/or ground?
Which one(s) will it disconnect? Can current on the ground pin keep draining somewhere even after this tripping? If so, does that mean GFCI automatically internally bootlegs/bridges its open ground to neutral under these tripping conditions?

Can the ground socket be used for grounding the following ground-pin-only items?

  1. a shielded ethernet cable's drain wire that's inserted into the
    socket via a ground-only
    plug    ,

  2. an ethernet surge protector that uses only the ground pin,

  3. surge protector power strip,

  4. anti-static wrist strap

Best Answer

Despite its name, a GFCI does not look at ground current - it only looks for a difference between the line and neutral currents passing through it. If it finds a difference of 5 mA or so (maybe 15 mA??) it assumes some current is going where it shouldn't, and trips, disconnecting the Line and Neutral.

The Ground pin on an outlet is intended to connect non-current-carrying parts of an appliance to Ground, to ensure the safety of users. If the Ground pin on an outlet is not connected to anything it cannot connect anything to Ground, and is useless.

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