Yesterdays house is mostly K & T, it is a 2 family, and the owner just recently installed GFCI outlets in several rooms.
When testing the device with the buttons, it tests properly, when using a tester, it obviousally shows no ground and will not test. I remember reading back at some point that a 2-prong system can have a GFCI and be wired to operate properly and will not trip if a tester is used. That appears to be the case here.
What I am trying to figure out is, if a normal 2-prong system has a 3-prong device installed without grounding it would be considered defective. Why would it not be the same case with a GFCI?
The owner (seller) indicated it was his understanding that in using the GFCI device (again which does properly test by the devices buttons) satisfied the code for a 3-prong non-grounded system.