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GFCI and K & T wiring


Neal Lewis
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Recently I've inspected three houses with knob & tube wiring where brand new GFCI outlets were installed for the ungrounded outlets on a K & T circuit. These were in rooms that typically don't need a GFCI outlet (bedroom, dining rm, etc). I believe the outlets were installed by an electrician.

Maybe I'm missing something, but I don't know what the reasoning is behind installing the GFCI outlet with the K & T. Maybe someone thought the occupant would be a little safer, but it obviously doesn't make the wiring any safer. Any thoughts?

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Recently I've inspected three houses with knob & tube wiring where brand new GFCI outlets were installed for the ungrounded outlets on a K & T circuit. These were in rooms that typically don't need a GFCI outlet (bedroom, dining rm, etc). I believe the outlets were installed by an electrician.

Maybe I'm missing something, but I don't know what the reasoning is behind installing the GFCI outlet with the K & T. Maybe someone thought the occupant would be a little safer, but it obviously doesn't make the wiring any safer. Any thoughts?

The GFCI enables them to use 3-slot receptacles without running equipment grounding wires.

- Jim Katen, Oregon

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...

Maybe I'm missing something, but I don't know what the reasoning is behind installing the GFCI outlet with the K & T. Maybe someone thought the occupant would be a little safer, but it obviously doesn't make the wiring any safer. Any thoughts?

It doesn't make the old wiring any safer elsewhere but it does make those particular receptacles safe to use with a grounded appliance (and actually safer with two-prong aplliances like lamps). The GFCI will trip if it senses an imbalance between the hot and neutral and does not need a ground wire for that function (unlike our GFCI testers). The homeowner might get a very brief buzz from a short to the chasis of a device but the GFCI should then trip.

You might want to read this... http://ecmweb.com/mag/electric_gfcis_work/

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Each to his own. I recommend that the wiring be replaced. GFCI's on an ungrounded circuit don't allow surge devices to function. They may also shock someone if the 'test' button is depressed if that someone is in contact with a ground. GFCI's often fail without the homeowner knowing it, leaving the outlet a hazard. Client deserves the full package.

Marc

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Correct, the NEC allows GFCI receptacles on ungrounded (2 wire) branch circuits but the "No Equipment Ground" sticker that comes with the GFCI is supposed to be installed on the face of the receptacle or cover plate. This tells the user that the receptacle isn't grounded although it looks like a grounded receptacle. A GFCI doesn't need to be grounded to properly function as its monitoring the current flow in the neutral and hot wires.

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