I would like confirmation on the following: Is any metal box automatically grounded if it is supplied by an armored cable (without a ground wire) that is properly connected to the box and back to the panel? If a metal box downstream on the same circuit is only supplied by Romex, I believe to ground that box I must pigtail the ground wires to a lug on the box - correct?
Armored cable without a ground connected to a metal box is not a proper ground. The Romex downstream would have it's ground connected to a lug or screw to the metal box but it still wouldn't be properly grounded because of the armored cable. Voltage testers would show a ground but it wouldn't be a proper ground.