"The left and right branches coming out of the over-the-sink light box are on different circuits.

Nods. It sounds like the original 12/3 feed to the light is a multiwire branch circuit (MWBC) with a shared neutral. From there, it divides into what, for all practical purposes, are two circuits on opposite poles.

Each circuit then runs to a box with an outlet and then to the respective appliances. The one on the right uses the red wire between light and switch to complete a switch loop to control the light. The one on the left switches power on the outbound disposal cable.

Where that leaves you is with two 12/2's, each of which powers an appliance where one of them is switched (circuit on the left) and the other is not.

You can handle this with a single non-GFCI receptacle by breaking the tabs that connect the terminal screws on either side of the receptacle. This is a normal design feature of a duplex receptacle. Take a pair of needlenose pliers and twist out the little bar so that there is no longer a connection between terminal screws on either side. One of the 12/2s will feed the upper half (hot to upper brass screw and neutral to upper silver screw) and the other 12/2 will feed the lower half using the other two screws.

You may, of course, have to replace one or more of the 12/2s from the outlet boxes if they aren't long enough to reach your new receptacle but, otherwise, you shouldn't have to rewire them.

A couple of additional notes may be useful:

1. Keep the neutrals separate and don't tie them together in any way!

2. If you want either or both sides of the receptacle to be GFCI protected, that'll depend on whether they are fed from the load terminals of the existing GFCI receptacles above them. (I'm assuming they are GFCIs and there's no reason to suspect that you need to change anything in the existing boxes unless you want to remove or add GFCI protection to either. Alternatively, it's possible that the entire MWBC is fed by a GFCI circuit breaker in which case everything is GFCI-protected per force.)

3. The circuit breaker controlling the two circuits (or single MWBC) should be a two-pole breaker such that when either path trips, both poles trip. Old code merely required a handle tie in this situation. New code (2008) requires a double breaker.

That's important here in that the old code only required handle ties or a 2-pole breaker when both poles connected to a "single yoke" (e.g., a split receptacle). Since you are adding a single-yoke fixture that wasn't part of the original wiring, you may need to "upgrade" this too.

4. Code requires two 20-amp circuits dedicated to countertop receptacles (an MWBC counts as two here). Depending on the purpose and location of the existing outlets, it may be a code violation in your area to tap dishwasher and/or disposal off of the required countertop circuits.

"From there a 12/2 goes down to the dishwasher, which the cable was just sticking out of a hole in the wall. Very sloppy."

Actually pretty common.
The DW will be hard wired without a cord or receptacle.
GDs are often treated the same way.

Some areas seem to prefer using a cord and receptacle to connect these items.
Hard wiring is more reliable, and they are both fixed items.

Thanks Terribletom. I think I understand what you said about wiring the outlet.

What about the wiring in the over-the-sink light box? That has me really confused as to how they all come together in the box. A 12/3 in and a 12/2 & 12/3 out. I'm going to try again to find the diagram I made.

The two circuit breakers involved (both 20) appear to be standard breakers, which just means this layman can't see any difference.

This house was built in 1982. The local code in this little town states to use the NEC code.

There were no GFCI receptacles but I am going to put them in and thought they would go where the two countertop outlets/receptacles were, next to the two switches. Yes? No? The disposal switch is on the left about a foot from the sink and the over-the-sink light switch is on the right about two feet from the sink.

Brickeyee

Thank you for replying. You stated:

>Hard wiring is more reliable, and they are both fixed items.

Agreed, but just punching a hole in the wall seems and looks shoddy. Is there any real problem using a receptacle?

What about the wiring in the over-the-sink light box? That has me really confused as to how they all come together in the box. A 12/3 in and a 12/2 & 12/3 out. I'm going to try again to find the diagram I made.

Although I can't be 100% certain without seeing it, here's how I envision your over-the-sink light box working:

The 12/3 MWBC power feeder enters the box with two hots--one black and one red from opposite poles--plus a shared neutral. The neutral gets connected to three white wires: one to feed the circuit on the left, one to feed the circuit on the right and the third is a "pigtail" that connects directly to the luminaire.

One of the incoming hots connects to the black wire feeding the circuit to the left. The other feeds the circuit on the right (it's unpredictable which ones are blacks and which ones are reds at this point). That leaves one leftover hot from the 12/3 that heads south on the rightmost circuit, right?

That one--the "leftover"--connects directly to the luminaire. It'll only get power when the switch below it sends power "back up". Make sense?

Now to the rightmost switch/outlet box. Whichever wire (either red or black) was connected directly to the light is connected to one of the switch terminals. The other--let's call it the "always hot" feed--branches out three ways: to the switch, to the receptacle and to the dishwasher. Exactly how it is wired was a matter of the electrician's preferences. S/he may have wirenutted the hot feed to two pigtails and the disposal feed. Alternatively, s/he might have used the second pair of receptacle screws to hook up to the dishwasher. Finally, the incoming neutral is connected to both the receptacle and the dishwasher feeder.

To the extent there's any mystery to this, perhaps you were uncertain about that third wire in the 12/3 on the right? It's just a switch loop return to control the light.

The two circuit breakers involved (both 20) appear to be standard breakers, which just means this layman can't see any difference.

This house was built in 1982. The local code in this little town states to use the NEC code.

Yep, they're just regular breakers. That's no surprise given the date of the house and the fact that, at that time, that pair of breakers didn't need handle ties because there was no instance downstream of both poles being wired to a device on the same yoke (something that will change if you add the split receptacle).

There were no GFCI receptacles but I am going to put them in and thought they would go where the two countertop outlets/receptacles were, next to the two switches. Yes? No?

I'm hardly surprised that GFCIs weren't used for kitchen counter receptacles in 1982 but, honestly, I don't recall off the top of my head when that became a code requirement. But, yes, I strongly recommend that you add GFCI protection.

You have two decent options:

(1) Change out those two side-by-side 20A breakers for one two-pole GFCI 20A breaker. Two-pole GFCI breakers are tad pricey, but this might still be a good choice in this case because it solves two problems at once: Tying the breaker toggles together and providing ground fault protection to everything on the circuit in one fell swoop. (With this approach, there's no rewiring required in those two receptacle boxes.)

(2) Install individual GFCI receptacles. This choice has these advantages: You'd save, oh, maybe thirty bucks and if you trip one of the GFCIs, the reset is right there at the countertop rather than in your breaker panel. (A small amount of the cost differential is offset by having to put in a handle tie if you don't install a two-pole breaker.)

"Agreed, but just punching a hole in the wall seems and looks shoddy. Is there any real problem using a receptacle?"

The hole for the DW is concealed when the DW is installed.
The only ones that will ever see it again are the DW installer and a service person if they need to pull the unit out for servicing.
There are also varying interpretations by AHJs about how long the cord for a DW can be (the NEC does limit the length).

A receptacle under the sink for a GD is one more thing to be disturbed and come unplugged, or make a poor connection (especially to the grounding conductor).
It is going to rarely be seen anyway.

It really depends on what the local AHJ wants to see.
I do know of one who wanted conduit (non-metallic or EMT) for GD feeds.
Everyone ended up using a short piece of EMT to an LB body mounted to the DW.
All it did is run up costs and make removing the GD more work.

TerribleTom: Even in 2008 it's not a code requirement to provide GFCI for these receptacles unless the equipment manufacturer requires it. Only the ones serving the countertop are required to have GFCI proteciton.

"Even in 2008 it's not a code requirement to provide GFCI for these receptacles"

Ron:

When you say "these receptacles", my reading of the info in the thread is that there are three receptacles potentially in play: two countertop receptacles and one new receptacle for dishwasher and disposal.

My (second) reply was in response to this question posed by the original poster:

"There were no GFCI receptacles but I am going to put them in and thought they would go where the two countertop outlets/receptacles were, next to the two switches."

I agree completely that there's nothing in code requiring GFCI protection for the one proposed split receptacle for the DW/disposal. On the contrary, one can make a decent argument against it if they're concerned about nuisance tripping from the DW/disposal.

The effect of the 2008 code, as applied here, has only to do with the use of a two-pole breaker instead of handle ties and does nothing to mandate a two-pole GFCI breaker covering the entire circuit or individual protection of the DW/disposal. Nor do I think that I implied that it did.

If the OP takes the "two GFCI receptacle" option for the countertop, s/he does not have to wire the DW/disposal feeds on the load side of the GFCIs. I think we agree about that.

strike that

Ron: Yes, I agree. The new split receptacle for the dishwasher and disposal does not require GFCI protection. Thanks for pointing that out.

Yes, I'm talking about the disposer/dishwasher not requring GFCI. The countertops do require them.

Thanks, Tom. Great explanation! I can actually understand it (well, most of it).

You wrote:

To the extent there's any mystery to this, perhaps you were uncertain about that third wire in the 12/3 on the right? It's just a switch loop return to control the light.

'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.

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.

""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.

You cannot share a neutral on the load side of a GFCI receptacle.
If you use GFCI receptacles for ALL the receptacles on a shared neutral circuit (no connections are made to the "load" side terminals of the GFCI receptacles) they will operate just fine.
It winds up the cost when you cannot use regular receptacles on the load side of the GFCI.
GFCIs cost more than even good quality duplex receptacles (let alone the under $1 receptacles).

'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.

Thanks Tom & Brickeyee

I'm learning a lot from you guys.

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.

Understood. If I go the plug-in route, I believe I've seen appliance cords for wiring in. I'll make sure it is the right size.

Another thing; Since reading up on 2 pole GFCI breakers, it appears the reason for these is to trip both circuits if one or the other shorts or overloads as with a 240 clothes dryer. Correct? But my two circuits (D/W & G/D) shouldn't need to trip together if one or the other has a short or overload. Correct? If so, can two 20 Amp single pole GFCI breakers do the trick? They are on separate breakers now. If not, what am I missing?

"But my two circuits (D/W & G/D) shouldn't need to trip together if one or the other has a short or overload. Correct? If so, can two 20 Amp single pole GFCI breakers do the trick? They are on separate breakers now. If not, what am I missing?

Nope, nope and nope.

First, the reason for the requirement that both must trip simulaneously is a saftey concern, not strictly a matter of overcurrent protection. Namely, although one circuit may be off, the shared neutral can still be carrying current from the other circuit.

Moreover, when two poles are wired to the same device ("yoke" is the code term), the potential consequences are even scarier. Walk yourself through this hypothetical scenario:

You decide to replace that split receptacle with one of a different color (or whatever), so you plug a receptacle tester into one of the outlet halves. Yup, the light is on. Then you turn off the breaker relating to that half. OK, fine, the test light is out and the circuit's dead, right?

So you unscrew the receptacle and as you're pulling it out you grab the hot wire feeding the OTHER half. ZAP! Surprise!

When two circuits are intertwined like this, the only safe way to service them is with both halves turned off.

Secondly, you cannot use two single-pole GFCI breakers because neither of them will "understand" the current on the neutral that's related to the power supplied by the other breaker. It simply won't work--they'll trip.

Secondly, you cannot use two single-pole GFCI breakers because neither of them will "understand" the current on the neutral that's related to the power supplied by the other breaker. It simply won't work--they'll trip.

Thank you, I stand corrected.

I found the diagram I originally drew and if I'm reading it correctly, the receptacle/O-T-S light switch box that the right side 12/3 goes into is wired like this:

The 12/3 incoming red goes to the top terminal of the switch.
Four blacks are pigtailed together; one is the 12/3 incoming black, one goes to the bottom terminal of the switch, one goes to the right side of the receptacle and one is the 12/2 black to the D/W.
Three whites are pigtailed together; One is the 12/3 incoming white, one goes to the left side of the receptacle and one is the 12/2 white to the D/W.

Does this help?

That's exactly what I'd expect to see in that box and it fits the description I gave above to a "T". What seemed slightly odd was this subsequent statement:

"It was a 12/3 going to the right for the over-the-sink light switch & receptacle then down to the D/W."

The way I took it, that sentence implied that 12/3 (not 12/2) continues from the switch box to the dishwasher. An ordinary dishwasher has no use for a third conductor.

As for the concept of a "switch loop", it's simple: the black wire in that 12/3 is "always hot" and is the source of power to the switch as well as everything else in the eastern hemisphere. The red wire runs from the switch back to the light and is only hot when the switch is closed ("on").

It's a "loop" because power runs from the box above to the box below and then back to the light above only when the switch is on.

If you want to visualize this in terms of a "traffic pattern", think of little electron-ants marching in line down the black wire. When the switch is off, they're blocked from getting to the red wire. When it's on, they go marching up the red wire. In the meantime, regardless of the switch setting, other electron ants keep marching to the receptacle and the dishwasher along those paths. :-)

Thanks, Tom. Sorry for not being clear enough in the original post. I think I've got a handle on it now.

One of the incoming hots connects to the black wire feeding the circuit to the left. The other feeds the circuit on the right (it's unpredictable which ones are blacks and which ones are reds at this point). That leaves one leftover hot from the 12/3 that heads south on the rightmost circuit, right?

I knew I'd be back. I'm on the O-T-S light box now. On the source 12/3 feed, the black connects to the 12/2 black on the left 12/2. Does it also connect to the 12/3 black on the right (seems it would have to)? And does the red from the source 12/3 feed pigtail to the red from the right 12/3 feed and to the light?

"On the source 12/3 feed, the black connects to the 12/2 black on the left 12/2. Does it also connect to the 12/3 black on the right (seems it would have to)? And does the red from the source 12/3 feed pigtail to the red from the right 12/3 feed and to the light?"

NOOOOOOO! There's more to this than simply matching colors.

If you wire it that way, everything you have--receptacles, diswasher, disposal--will be on one half of the circuit except the one small light which, to the extent it works at all, will be the only thing wired to the second 20A half of the so-called (at this point) "MWBC".

As long as the light switch is off, the light will stay on 100% of the time. If you turn the switch on, however, you'll have an instant 240V short circuit and (we hope!) both breakers will trip instantly.

Whether the switch and/or light and/or you will survive the trauma is anyone's guess.

(I'm serious, BTW!)

If you promise the wire colors you gave for the switch box to the right in your post @ Sun, May 31, 09 at 18:17 are as stated there, follow this color scheme in the upper box:

From the source 12/3 feed, the black connects to the 12/2 black on the left 12/2 and the source red connects to the 12/3 black! on the right.

The red from the 12/3 cable that runs between light and switch connects to the light. (And, as you've cross-your-heart promised, the other end of that red connects directly to a terminal on the switch, ok?)

There is no red pigtail in this wiring "diagram". Nada. Nul. Nichts! None. The only pigtail in the upper box is a white neutral that goes to the light.

Thanks Tom. I studied it long enough and did eventually figure it out. I tried to post a response to that effect, but it wouldn't let me post two in a row.

(And, as you've cross-your-heart promised, the other end of that red connects directly to a terminal on the switch, ok?)

Loved that!

I hooked up all switches and recptacles and fired it up. No breakers tripped and all worked as they should. The top of the under the sink receptacle switches on and off for the G/D and the bottom stays hot for the D/W. The box on the countertop (right) switches the O-T-S light on and off.

This part of the kitchen remodel took awhile but thanks to you and the others, it's done and done right. It was a great learning experience...............and I'm still alive!!!

but it wouldn't let me post two in a row.

Change the title "Disherwasher, Disposal Wiring on One Outlet" by one or more characters on your second post and you can post again.