receptacle tester

[John Dirks Jr]

If under normal conditions there is no current in the grounding system of a house, how does our 3 prong tester determine if the system is grounded or not?

[Matt Fellman]

They just measure a voltage difference across the three possibilites and report if it exists. If there's no ground there's nothing to report... therfore the light is out.

Hot - Neutral

Hot - Ground

Neutral - Ground

Here's a cool link that has a lot of good info:

http://www.thecircuitdetective.com/test.htm#general