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Posted by dan1980 (My Page) on
Thu, May 6, 10 at 17:59

Have an old house with knob and tube wiring that has had newer wiring added over the years, hard telling what's behind those walls. Have some gfci's that show reverse polarity. The wiring seems correct(black is showing it is hot and on the correct side of gfci). Switched wires, same results. Even put new gfci in. I am stumped. Anyone ever had a similar situation. House is to be inspected and needs to have this fixed.

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A missing ground conductor will cause incorrect readings on many 'receptacle testers.'


Without a ground there's no way to tell polarity. You have to have a reference.
As brickeye points out, having unterminated connections will cause enough induced voltage to trigger a high impedance meter or light up the little bulbs in these things.

To be sure, find some known ground (perhaps a water pipe) and measure between the small slot and that (should be 120V) as well as between the two slots.

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