We've all seen AC line testers, with three lamps that diagnose the wiring of an electrical outlet (well at least in Canada/US).
I'm (somewhat) used to the type that use neon bulbs, so I have two related questions:
1) How do the more modern sorts with LEDs work?
2) How do any of them avoid tripping ground fault interruption protection?
I want to build a special power bar for my repair work and I think it would be useful to build this diagnostic feature into that power bar.