Replacing receptacle & switch on a MWBC in kitchen

Question

Background:

The house was built in 1983. Previous owner(s) have been creative on some DIY projects around the house. The receptacle was wired half direct & half sideways.

Problems:

The switch on the right of the combo controlling the fluorescence lighting in the kitchen ceiling no longer works. The receptacle on the left, (Both HOT), working independently from the light switch also no longer working and there's some debris inside some of the slots.

The wiring inside the box.

These are the parts I purchased that are similar to the old parts. The pigtail actually is a mystery, it fell out when I removed the faceplate. I would appreciate some feedback on that and see if it should be replaced and rewired correctly.

A picture showing the breakers placements.

Issues to rectify:

Replacing everything as is safely. Will work on having upgraded when we will redo the kitchen couple years down the road.

Welcome any constructive feedback and thanks in advance.

BELOW ADDED AFTER INITIAL QUESTION BEING ANSWERED.

Seeking more clarification and also acknowledgement on my understanding of the suggestion, a few more questions if you don't mind as it's my first time dealing with such a situation.

Here's the self-ground receptacle that I just purchased from a home hardware store.

This set of wires to be attached to the receptacle, right? I was going through my notes of the old set up where the red (top) & black (bottom) were wired at the back. I will be rewiring them on the sides this time to increase the reliability, so the red should remain on the top screw and black on the bottom? I will also break the tab in between the screws.

As for the other 3 black wires, I am a bit confused. So, I labelled them 1, 2 & 3 in the picture to get a better perspective.

Just wondering if I understood correctly, so the capped one (3) should be uncapped and wired to the switch?

Additional findings since I first posted, I found out that lights both indoor and outdoor by the front door, a set of lights and an exhaust fan of the guest washroom, a kitchen ceiling light with a dimmer and also a range hood are all wired to the first breaker with the fluorescent ceiling lighting as well. Just curious... is it acceptable to have so many items attached to 1 breaker.

Thanks again for all your feedback and help.

Answer 1

Nice work figuring out which breakers they are. That is not an easy one to diagnose.

Properly grounding

Since this is a metal box, All ground wires must go to the box first. They can be pigtailed to the switch if you really want to, but it's unnecessary, as it will pick up ground via the mounting screws. If the receptacle is a higher quality one labeled "Self-grounding" (not like that cheapo in the photo), then it too can pick up ground via the mounting screws and doesn't need a ground pigtail.

So the MWBC ground wire should be landed on one of the numerous ground screws in the back of this box. Either run a ground pigtail to the receptacle from another ground screw (you'll need to buy 8" of wire for that), or switch to a spec-grade ($3) receptacle which has the self-grounding feature. I would do the latter, as it's a much better built receptacle all-around.

Note that kitchen countertop receptacles need to be GFCI protected. In an MWBC that can only happen at the breaker ($90). Use of a $16 GFCI receptacle means you must choose red or black as the only hot wire in use, and cap off the other, which is a bit of a waste.

Circuits must be kept separated

While it's perfectly normal for the 2 hots in a MWBC to share a neutral (that's what a MWBC is)...

... it's illegal and dangerous for that neutral also to be used by a 2nd circuit (3rd breaker).

Since you have identified a 2-pole breaker for the MWBC, we can probably guess that both "hot wires" on the MWBC are connected to that breaker. So that confirms it is independent from the MWBC.

A neutral wire must only serve its partner hot wire(s). When you have 2 separate circuits in a box (the MWBC and the single), there must be a "virtual divider" between them, where nothing crosses the divider except safety ground. Neutral must not cross.

There are 4 cables coming into the box:

• a /3 cable that is definitely the MWBC
• Two /2 cables whose hots go to "shepherd's hooks"
• one /2 cable whose hot is capped off

Here is what I suspect.

I feel that often, the simplest answer is the correct one.

Note that all the /2 cables have their neutrals joined. So if neutrals have been handled properly, that means they're all on the solo circuit (not the MWBC). I gather one is supply, another is "ongoing" to other switches or lights, and the third is switched-hot to the now-defunct fluorescent lamp. That's alright.

That would then suggest the /3 cable goes to the socket only, and that is the MWBC. Makes sense. If you hook red and black to the receptacle, you must break off the tab on the "hot" (brass screw) side of the receptacle. Otherwise, bang boom.

While one of the /2 blacks is over on the left side, I doubt it went to the MWBC. Both hot screws on the socket would already be used by red/black from MWBC.

As for the pigtail, I gather the last guy who was in there was confused by all of the above, and tried the pigtail and it didn't buy them anything. Use it if you need a pigtail for something. Remember the el-cheapo receptacle needs a ground pigtail to the box.

On the switch wiring, I would expect having the 3 black wires separate has caused some unrelated loads around the house to break. Joining two of them (supply hot and onward always-hot) should restore power to those things. The remaining black wire is switched-hot to the fluorescent lamp.

That is another good use of a pigtail - to join the two "always-hot" blacks to a pigtail, so the pigtail can go to the switch. It's also possible to use the switch itself as a splice, by putting 1 wire on screw and 1 on backstab, but that involves using backstabs, which are unreliable.

In response to edit:

On the /3 cable the ground needs to go to a ground screw in the back of the metal box. That will be the end of your grounding task.

Yes I think you have the receptacle wiring correct.

On the black wires to the switch, I'm not entirely sure which pair should be together and which one should be alone. But your idea is my first guess. Nothing should go boom if you get it wrong.