No Ground wire but GFCI tester says the outlet is grounded
I turned off the power and removed the old outlet and noticed there's no groud wire. It's an old building - 1950s.
After doing some research I went out and bought a GFCI tester. I tested the old 3-prong outlet with the GFCI tester and it came up as "correct". So I assume it's being grounded some how.
Is it being grounded through the metal box?
Can I still isntall the KP200 outlet with out a ground wire?