I stumbled upon a situation while making some mild upgrades to my kitchen. I will try to be as detailed as possible to minimize follow-up questions.

I have two switches next to the kitchen sink; one controls a light over the sink, and one controls the garbage disposal. I opened the box containing the switches because I wanted to remove the light and light switch and upgrade the disposal switch to a rocker style. I'm pretty comfortable with these minor things, and assumed it would be like other small DIY jobs I've done.

Instead, I found a wiring setup that is beyond my comprehension as a non-electrician. I've made a wiring diagram for the four cables coming into the box, the wires in the box, and the switches. I have labeled the cables for easy reference, but please let me know if you see anything that requires additional explanation. Diagram: https://imgur.com/yhghSpg

The overhead light was a standard recessed light, nothing special about it. The garbage disposal is a 9.5A/120V InSinkErator. Next to the sink is also a 15A/120V Samsung dishwasher. These three things all share a circuit breaker (in that when I turned the power off at that breaker, all three lost power), and they are the only three things on that breaker. I have tested every light and receptacle in and out of the house to be sure.

The related circuit breaker appears to be a 15A double pole breaker. It has one red wire going into a cable in the ceiling, and a black wire going to a cable that appears to go into the floor. Photos of circuit breaker: https://imgur.com/glnfbD5 and https://imgur.com/u0Z4NJ1

I have two questions/issues here.

  1. On the diagram, you will see two black wires coming into the box that have a diamond shape at the end. These wires are not connected to anything, and there is no indication they were ever connected to each other (which wouldn't make a lot of sense to me, but I'm no expert). Photos: https://imgur.com/FAu5jJg and https://imgur.com/MBKLQ1l I used a keyhole saw to cut the drywall around the box, but never went anywhere near the inside of it. Why would I have two hot wires that are not connected to anything? I am afraid to do anything (especially turn the power on, since I cannot be 100% sure that I didn't somehow cause this) until I understand why these are like this.

  2. Assuming I'm crazy and worrying about nothing, and this is a fine wiring setup, I still want to remove the light and light switch. How can I rewire this and still make sure that a) I don't burn down my house, and b) my garbage disposal and dishwasher will function correctly?

I appreciate any assistance you all can provide. If the answer is "call an electrician," that's okay; I'm already leaning that way. Just trying to save a few hundred dollars if I can.

  • 3
    Normally a double-pole breaker would indicate a Multi-Wire Branch Circuit (MWBC), but the black and red going different places in the panel doesn't fit with that and is likely a code violation. Does a black wire go into the switch box? Also not clear how the dishwasher connects - but dishwasher and disposal/lights on two halves of an MWBC is relatively normal. Commented Jun 30 at 3:46
  • 1
    Do you have a non-contact voltage tester? If not, get one (a cheap one is fine) and check if those black wires are hot when you turn the breaker back on. If they aren't then I would guess someone re-purposed what used to be a MWBC into two separate circuits. If that's the case you may be able to fix this mess by replacing the breaker with two single-pole breakers (assuming the neutrals for the two circuits aren't connected). If they are hot then it's probably more complicated. Commented Jun 30 at 10:27
  • A kitchen is one of the most likely places to find a MWBC, or several, due to the large number of required circuits. They are easy enough to understand if you do a bit of reading. Please add pictures of the wiring - written descriptions are hard to follow, and written descriptions by people who don't fully understand what they are looking at are often incorrect - pictures that clearly show all connections are far more accurate.
    – Ecnerwal
    Commented Jun 30 at 12:24
  • I appreciate you all taking the time to answer. I will pull out the multimeter and see if the black wires are hot and then try to add more context.
    – DIY Dad
    Commented Jul 1 at 11:48
  • One possibility is that someone rewired the dishwasher and abandoned "Cable 3" in place. Technically, a MWBC can leave the panelboard through 2 separate cables, it's just unusual. Commented Jul 2 at 14:48


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