What Causes This?

[ROBERT W. NEWLAND, JR.]

I had a living room outlet that has the top outlet controlled by a wall switch (for lamps). When I checked the outlet in the "on" position my tester checked OK. When the switch was turned off, my tester had a very weak (dim) light indicating an open neutral. Any ideas what would cause this indication? Thx.

[James F. McKee]

switch used to break white wire instead of black ???

[Marc D. Shunk]

It's called capacitive coupling, and will occur with 3-wire cables. It's not a problem or a hazard. Just a phenomenon.

[David A. Andersen]

A bright light indicates the condition, not a dim one.

[Michael Larson]

Get a Wiggy and remove the doubt.

[Jeffrey R. Wicklander]

Originally Posted by Marc D. Shunk

It's called capacitive coupling, and will occur with 3-wire cables. It's not a problem or a hazard. Just a phenomenon.

Marc,
Capacitive or inductive?

Jeff

[Marc D. Shunk]

Eh, probably inductive, in this case.

Do this experiment. Plug in the hot and neutral (white and black) of a 3-wire cable into a hot receptacle, then use a meter to check from the unconnected red wire to the white neutral. You'll get a voltage reading, and it can light up a neon lamp, such as are found in those plug checkers.

[Michael Larson]

Originally Posted by Marc D. Shunk

Eh, probably inductive, in this case.

Do this experiment. Plug in the hot and neutral (white and black) of a 3-wire cable into a hot receptacle, then use a meter to check from the unconnected red wire to the white neutral. You'll get a voltage reading, and it can light up a neon lamp, such as are found in those plug checkers.

That's the problem with high input impedance meters and neon light testers.

Because they put no load on the system they can give false or misleading readings.

Try troubleshooting vehicle wiring with a multimeter. Good luck.

[Bob Elliott]

It is related to being able to light neon and flourescents with a high frequency tesla coil.
Inductive as Marc said.