Does anyone know how sensitive those little three prong circuit testers are? We were using them to confirm ground in the 110 outlets in our plant, but recently discovered that they can be misleading. One of them registered a gound ok but the ground measured 1700 ohms. We are now, of course, going around with a proper VOM rechecking all receptacles.
IMHO, I wouldn't use one of the cheapo ones for anything commercial at all.
Those testers use neon bulbs, which can light on a milliamp or less of current flow. They tell you only that there is some kind of path to ground, not that it is a GOOD path.
Thanks guys. We are no longer using these things in the plant. I never really thought much of them anyway, but we were sucked in by OSHA. There field agents use these same chepo gadgets to check for grounds during their investigations.
In New Zealand we use the AVO-Megger LT 310 Loop Impedance Tester on the 230 volts MEN system.
The best way to test is to use a loop impedance tester instead of relying on neons which can give you false readings.
This one imposes a test current between the phase and neutral and earth.
It will tell you in Ohms and kiloAmps what fault level is available.
it will also confirm that the polarity is correct.