>Whoever pulled the cable through just smashed the wallboard with a hammer and left a hole exposing the studs, insulation and exterior house sheathing. Don't you just love quality workmanship? OK, depending on what zone you're in, this may raise the issue of moisture migration into, and condensation inside, the wall cavity during winter months (think mold, rot, crumbling drywall, etc.). I know there are products to mitigate this for electrical boxes, but I have no experience with them. jmvd20 and pjb999 make valid points suggesting installing a receptacle in the wall, and a cord on the dishwasher to run to it. That's how I did ours. In fact, IIRC, there are more stringent NEC requirements for hard-wiring a permanent dishwasher compared to it being "portable" which, in the eyes of The Code, it would be if it could simply be unplugged. If you do decide to go this route, just be careful. Most (all?) 15 and 20-amp residential switches and receptacles accept #12 and #14 only. You will likely need to splice in short #12 whips to go between the #10 wires and the receptacle.

Sounds like you are using a non contact tester. You will always get a false positive with a non contact tester on a multiwire circuit, and on a 3 way switch cable. It is because the tester works by detecting the magnetic field which surrounds an energized wire. If an energized wire is alongside a non energized wire, it will have a magnetic field induced into it that will fool your tester. However, you will notice that in reality the non contact tester will activate on a true live wire at a greater didtance than a wire with induced voltage. The wire with induced voltage will usually have to be almost touching the tester. The only way to know for sure is to use a Wiggy. Or just shut off both breakers.

'splain please. It was a 12/3 going to the right for the over-the-sink light switch & receptacle then down to the D/W. You got me scratching my head on that one! I don't have a clue why there is a third conductor running to the DW. It might be worth looking at the termination of that wire. My hunch is that one of them is unused, but who knows? "I think the Two-Pole GFCI 20A breaker is a great idea. The breaker box is in a back bedroom so if it trips, no biggie in getting to it. Also, I read this while Googling Two-Pole GFCI 20A breakers: 'GFI devices cannot operate on circuits with shared neutrals.' True? False? Isn't that what I have (circuits with shared neutrals)? Just trying to cover all bases." That's a great question. As of maybe five years ago, I think the correct answer would have been "true". (How old was the source of that information?) But now, there are (at least) two types of two-pole GFCI breakers. The simple 240V two-pole versions will not work, because they only measure current imbalance between the two opposite-pole hots. These may have a white pigtail to the neutral bar, but that's only to power the internal circuitry of the breaker (essentially 120V). The second type--designed for 120/240V circuits--will work on an MWBC with shared neutral. These have a lug on them to attach the shared neutral as well as a pigtail to the neutral bar. Basically, they compare the output of the two hots and, if they're out of balance, they measure the current on the neutral to account for the residual difference. The bottom line is that it's important to make sure that the breaker monitors the neutral current and is suitable for use on the MWBC. (Also, it is possible that not all manufacturers offer a compatible breaker, especially if your main panel requires an old, discontinued or scarce breaker type.) BTW, your question made me rethink my estimate of a $30 cost differential. Those 120/240V GFCIs were quite expensive when they first came out a couple of years ago and I'm not sure how much they've come down in price. I may be too optimistic on that guess about price, so you might want to look at price/availability before you decide which way to go. (Also, if you can't find one at a big box store and have to go to an electrical supply house, they have a way of gouging a one-time walk-in DIYer with a ridiculously high "list price"!) *** Broaching a related issue here. If you go the route of changing the hardwiring to "plug in", I hope you're aware that you'll need to retrofit the appliances with proper cords and plugs. You shouldn't just put a new plug on the romex tails! "Retrofitting" is probably more easily done with the disposal, since they frequently come with a plug-in option. But dishwashers? Not so much.

You can use any NM or even AC90 or THHN/THWN wire that is 14 ga or thicker. The 15A breaker demands a minimum of 14 ga but there is nothing wrong code wise with going with a thicker wire except for convenience of working with it and the price. In the future if someone saw 12 ga wire they might assume a 20A breaker. It's not best practice to mix wire sizes on a cc't, but it is code compliant.