JoeMed

Mine sits in the car, depending on the age of the house. 1975 is the mark that I pull it out and use it. Agreed boot leg connection is rare but I do find ungrounded systems with a ground at the receptacles? Some where is an accidental ground or an appliance that is connected and has a connection. These older systems are when I pull out the Sure-Test device. Yes, expensive and bulky, it doesn't fit into my pouch. Maybe next year I'll get the new smaller version. Last week in the same house (5 years old) I found a GFI that only worked at the TEST button and another that did not work at the TEST button, but my "night-light" tripped it?? I asked the owner if they would give me the old devices to use as a sample testing for other inspectors. Joe thanks for the welcoming, nice forum. These sites are a wealth of information and experience.

The limitations and missreadings come from incorrect grounding. If the neutral is jumped over to the ground, the 3 prong will respond "Correct Wiring", and will typically trip the device. No one was the wiser. OR The 3 prong could determine that the device "appeared to be" wired correctly but the device does not have a ground. Thus the tester would not trip the device, but the TEST button on the device did function. The 3 prong tester is an indirect gross test of the GFI function buy diverting some of the curent to the ground. This is what makes the GFI circuit "unbalanced" and trip (sending power to the ground is not a controlled amount of voltage, like the required 4 mA to 6 mA to trip a device) The sure test can determine, thru resistance, if the neutral is connected to the ground. It will also determine the amount of milliamps the device needed to trip. It will test the GFI if it is installed on an ungrounded system. The 3 prong will determine that it is ungrounded, but it needs a ground to function and test the GFI. I hope this clarifies the limitations of the 3 prong tester. Joe

The correcte way to test a GFI is a great debate on several forums. UL and the manufactures only recommend and acknowledge the "TEST" button. UL link http://www.ul.com/consumers/groundfault.html I use the 3 prong tester just like everyone else on newer homes. I made a testing board with multiple GFIs all wired incorrectly and let fellow inspectors use their 3 prong testers to try and find the incorrect wiring. Many of the defects can not be found with the 3 prong tester. The Ideal Sure Test was accurate every time. Joe