Tear it all out to the studs and subfloor

>NEC actually allows disposals to not be on a GFCI, due to false trips

You raise a good point and are technically correct. Still a good idea anyhow.

While I wouldn't personally put both a dishwasher and disposal on the same circuit, as long as the draw from both don't add up to more than 80% of the rating of the circuit, they can be combined.

Do you set it just to stay on for a couple hours?

Thanks! That is indeed a very elegant and straightforward fix. Just keep them hardwired but do the splice in an actual junction box. Don't know why I didn't think of that. lol

The only real advantage I see personally to adding outlets and converting the appliances to plugs is that Home Depot's installers expected that. As long as the only real code compliance thing with the original setup is the point of the splice being in the dishwasher, this could be the way to go.

No need for PD. If you're designing a dashcam that needs more than the standard 5 V × 500 mA = 2500 mW of power on a normal USB port, you're doing something very wrong.

Believe it or not, the neutral carries exactly the same current as the hot, when connected in a circuit.

Turns out it was a high limit sensor that wasn't resetting.

Ha, I bought some smart switch for my old house and learned this the hard way! The neutral apparently carries a tiny bit of current that the smart switch uses to keep its settings of something like that.

It's not code. It's overfilled.

Good Lord what a mess.

Dishwasher and disposal commonly share a circuit in new construction.

Appliance guy here.

What you're describing isn't right, but is very common.

The fix is fairly straightforward.

Reroute the wire feeding the dishwasher to the space under the sink. Install a surface-mount junction box, and run that wire, and the wire feeding the disposal into that box, then run a new length of wire to feed the dishwasher.

All the wiring for your disposal essentially remains the same, you're just no longer using the tiny jBox on the dishwasher as your splice point.

Picky detail here: First, all of the parts for this wiring should be rated for 15 amps.

EDIT: I missed the fact that you're describing everything in terms of 12 gauge wire, which is to say, the wire gauge and all other details that are appropriate for 20 amp circuits. My experience has only been with 15 amp GFCIs, so that's what I wrote about. It doesn't matter which amperage rating you wire for, as long as it's done properly. One example of this "properly" is that if the feed Romex were 14 gauge, you would not be allowed to wire up the rest of it using 12 gauge. The way to think about this is: As you go further away from the panel, you either use the same wire gauge or smaller wire gauge (see my note somewhere else here... smaller gauge means larger wire gauge number).

Second, your final drawing shows the correct wiring but... look up a 20 amp outlet. Your drawing intends to show outlets rated 20 amps, where the hot plug holes are vertically oriented and the neutral plug holes are horizontally oriented. But it shows 15 amp sockets, where the hot and the neutral holes are both vertically oriented. This is minor in this discussion, but if someone decides to get this exact hardware and wire it up EXACTLY as shown, there can be difficulties. (Plus, this particular set of wiring parts should be 15 amp rated, not 20 amp.)

Don't be confused when you read "(if less than 14 gauge,...)."

I know how this should be wired but I don't know how to interpret the part in parentheses above. See, a wire that is smaller in diameter, which could be described as "less," has a HIGHER size number; a wire that is larger in diameter has a LOWER size number. For instance, 14 gauge wire is thicker than 16 gauge wire.

Going the breaker route probably won't be cheaper. Depends upon your electrical panel. GFCI/AFCI breakers can easily be $70.

If I were you, I'd just get the GFCI breaker and not worry about the AFCI. There's some debate as to whether they should be used or not.

You need a disposal button. They just hardwired the dishwasher and the disposal switch. https://www.homedepot.com/p/InSinkErator-Dual-Outlet-Sink-Top-Air-Switch-Kit-w-Satin-Nickel-Button-for-Garbage-Disposal-Instant-Hot-Water-Dispenser-STS-OOSN/304076179?

That would be my guess as well. I probably wouldn't mess with it if it's working, just know that if there's a block, that's a good place to look.

Thanks. I'm a total newb to all this and it's taken me days to get to this point, so I have no idea what replacing the breaker would entail. But I'll look into the possibility of doing that since using a standard outlet with half-hot switch wiring would be easier and cheaper.

No. Current code as of NEC 2017 requires that all j-boxes with a device have a neutral wire. This includes switches. The neutral wire gets capped off when not used by the switch.

It's to allow for potential future devices like smart switches.

Yep it worked great, it got sanded and refinished, so it was a momentary pain in the ass to restore some Dade county pine floors. It is not like I mopped it with gasoline, Diesel is not explosive or highly combustible.

Lol, should be similar on other car brands too!

USB-C with high USB-PD wattage

I would scrape it out and use mortar, not mastic. You can also use "patchcrete" its already mixed and comes in smaller tubs if the repair is fairly small, it will keep you from having to buy a 60lb bag.

For real. It wasnt that long ago when nearly every piece of trim in both of the vehicles I owned had screws, and pretty much only screws.

When you use any kind of specialty switch, like (obviously not relevant here) a motion sensor, timer, etc. a neutral is best. There are motion sensors that pull a bit of current through the circuit itself, but they are terrible at best and often don't work with LED lighting, which is also code now.

I suspect the code mentioned is meant to prevent shoddy sparkies from lazily grabbing neutrals from nearby circuits, which can result in shared neutrals (ask me how I know this).

I can't honestly think of a reason why you'd use anything other than a dumb toggle switch for an under-sink cutoff for a DW/Disposal, but it's probably easier and safer to just say "all switch locations need a neutral" than to specify "except under kitchen cabinets where the switch is only used for an appliance cutoff".

From my brief googling of the difference, I think you are right that it is a sanitary tee, not a wye.

I took another photo from a different angle:

https://i.imgur.com/UKixPEl.jpg

I suspect that the disposal was added after the fact, which would explain a lot of this. I guess I could knock out the plug and put the drain into the disposal and just cut and cap that whole drain from the air gap. I haven't decided but I'd probably go with the path of least resistance since this has been working.