I was replacing a light fixture and I noticed that my voltage tester would light up when I had one prong on the hot cable and another prong touching the metal box. Is this a problem? Does it mean that the box is not grounded?
Actually, just the opposite. It means the box is providing acceptible ground for the hot lead to travel through the circuit you are creating. It means that the hot lead is hot and the box is a good ground.
Well, providing that its not actually a "voltage" meter thats "lighting up". I am guessing its a neon tester with a bulb that should light. It means everything is A-OK.
This is a way you might test for power before touching a wire, to make sure the circuit went out after you shutoff a breaker.