Old K&T wiring had all black insulation. The hot was black, the neutral was black, and there was no safety ground. To make it even more confusing, many times the (black) neutral was run to the switch for the lights. So unless you compared the voltage to an earth ground, it was really easy to get confused.
Later K&T wiring was sort of gray (neutral) and black (hot), but after 80 years of oxidation, everything looks like the same color. Again, it's very easy to get the hot and neutral reversed when connecting to K&T.
Of course, it's a code violation to do any sort of bootleg ground, or to tie into open K&T wiring at all. And you're supposed to convert any 2-wire receptacles to a 3-wire GFCI with an unconnected ground screw. Since a GFCI doesn't require a ground wire to operate at all, then the consumer is safe from shock. However, the receptacle is supposed to be marked as "No Ground" but I've never seen one marked like that other than my own installs. Maybe I haven't been looking hard enough.
Just how do you guys deal with "upgrades" to grounded receptacles in old buildings?
Mike Sokol
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