If you are using a multimeter, testing hot to the box is not a good idea or needed, if you accidentally touch the box your gonna get zapped. If you ever tested hot to ground, it would make the breaker switch, if the box was grounded it would do the same thing.

If you are talking about non contact voltage testers, it depends how sensitive the voltage tester is, and if it is working properly also. I have had one that (when it worked) would detect voltage through the box. That tester later started giving me unreliable results and I had to toss it. I previously did not know that those things go bad but its common. I now have a klein tools tester that you have to touch the wire directly to test voltage. Gives a much more reliable result. Also that old tester I used to have, if there were 3 lines by each other you wouldnt be able to test each line separately unless you pulled one away from the others.

The cheap one I had went bad after about a year and I did try new batteries also. The one I use now is http://www.homedepot.com/p/Klein-Tools-Non-Contact-Voltage-Tester-NCVT-1SEN/100661787 It is about twice the price of the cheaper testers but much more reliable and longer lasting.

When you run a live wire through a hole in a metal box, the magnetic current produces a voltage on the metal box that a pen type tester can pick up. It can also happen with long runs of parallel wires. This result from a pen tester is usually nothing to worry about, BUT, When putting wires through a hole in a metal box, the hot and neutral from the same circuit need to go through the same hole to cancel out this transformer effect. In essence, this is the principle of how a GFCI detects an unbalanced current. This could indicate that there are neutral wires from other circuits tied together with this circuit somewhere down the line.

" I also checked voltage from hot to the box and there is 1 V. How can that be?" Hard to say without being there. What is the voltage from the box to ground, or neutral? What is the box sitting on? I have had small voltages from a couple different situations caused by metal lathe. 1 volt is fairly minimal, and could be caused by anything. In fact, I just touched one lead to a breaker terminal in a panel, and my meter read 1 volt without touching the other lead to anything at all. And when I touch the other lead to an aluminum bar that touches the concrete floor, I get 3 volts. In other words, the box is touching something with just enough resistance to still allow a 1 volt reading.

"Is the hot leaking through the romex?" Doubtful, other than in the way I described above. If the hot was leaking in the way you are thinking, the voltage difference would not be measurable because it is the same voltage coming from the same wire you are testing to. It would be more like touching both probes to the same wire, and you would be getting shocked when you touch the box. If it is only 1 volt difference, then the box would be 119 volts to ground.

"I'm concerned to connect the ground to the box if there is voltage." Go ahead and connect the ground. That is what it is for, to help facilitate the tripping of the breaker if there actually IS a problem.

Thanks Fred. It sounds like everything is working as expected. I have two lines coming into the box from different holes, but each line coming in has its own hot, neutral, and ground still in the romex sheathing so I don't think there is a transformer affect happening. I'm guessing my tester is just being overly sensitive as everything else is metering out correctly.

PS- that was what I was talking about with the meter, other than I wasn't reading through an outlet, but the actual wires.

I'll hook the ground up and test it again before throwing the switch. Thanks

Before you hook up the ground to the box, just for curiosity, check the box to ground and box to neutral voltage. If you are registering anything that way, then you may have a transformer effect due to neutrals tied together from different circuits somewhere else. Didn't figure you would have a problem right at that box due to the romex. That was just the long way around explaining how the neutrals tied together somewhere else could cause the same thing. Of course, things (lights etc) on that circuit have to be turned on to see that voltage.

Will do. Thanks

Fred, question. If you were set to measure Amp on the multimeter and tested hot to ground, would that cause the problem I was thinking would happen? I was clearly wrong with what I said but I was thinking it would be like crossing your hot and ground wires. FYI, I dont normally test current with a multimeter so no worries there just being theoretical. I know its a lot more complicated than voltage to do it right and be safe.

There are so many different kinds of multi meters it would be hard to say for certain what would happen. Some may just blow a fuse in the meter before the breaker trips, while others may ruin the whole meter. It may or may not trip the breaker in the process, but certainly could. I rarely use that type of series meter to test amperage. It is maybe more of something you would do to repair appliances or test if a motor was adequate for a task etc. For house wiring, I use one of these that works on the same transformer principle being discussed here.

http://www.fluke.com/fluke/tten/Electrical-Test-Tools/Electrical-Testers/Fluke--T5.htm?PID=55986

A voltmeter measures in parallel to the circuit, so it has its own resistance to keep from being a short circuit. An ammeter measures in series with the circuit being tested, so it relies on the resistance in the circuit such as a lightbulb to keep it from being a short circuit and therefore tripping the breaker.

I have a Fluke meter that also has an amp clamp. I didn't have anything switched on (no lights or anything) so there wasn't any current running though it, only voltage. Mine is actually pretty simple. It autoswitches between DC/AC. Pretty much all I need to set is A, V, continuity and that's about it. For diagnosing basic wiring, it's pretty decent.

...funny...I clicked on the link AFTER I typed all of this...That's the unit I have.