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I have a condo unit built in the 1990s. The garbage disposal on/off will trip the circuit breaker every time it is turned on. The panel shows that the dishwasher and garbage share 2 15 Amp circuit breakers. In other words, 1 breaker controls the overhead microwave and disposal, the next breaker controls dishwasher and kitchen lights. (Sorry I’m not there at the moment so doing this from memory, not sure of the exact appliances labeled). The outlet underneath the sink is not GFCI and furthermore interestingly enough labeled with Dishwasher on the top three prong outlet and Disposal on the bottom 3 prong outlet. The garbage disposal works fine, nothing is stuck.

I bought a new plain old entry level GE dishwasher yesterday and connected it with a rated 13 amp plug bought from Home Depot. It’s hard to say if the outlet was working before, because the old tenant hadn’t used the old dishwasher for a few years, which I replaced because of the age. I’m going to suspect that the combo of the new dishwasher plug and old disposal has something to do with this issue. I also changed the underneath sink outlet with both a 20 amp GFCI outlet and a 15 amp GFCI outlet with no luck. I also changed the on off toggle switch for the garbage disposal, with no luck. If I plug the dishwasher into a different outlet, it works fine. The same with the garbage disposal, but of course I’m not able to toggle switch it to turn off.

I’m almost ready to hire an electrician but wanted to see if there’s anything else I can try.

I want to describe more in detail on the ordering of things:

  1. The garbage disposal worked fine and we left it as is

  2. we removed the dishwasher as it looked beat up. No idea if the old dishwasher was working previously.

  3. we wired up a 13amp rated plug to the dishwasher. The dishwasher is a GE dishwasher: https://www.homedepot.com/p/GE-24-in-Stainless-Steel-Front-Control-Built-In-Tall-Tub-Dishwasher-with-Steam-Cleaning-and-52-dBA-GDF550PSRSS/318022460

  4. Used this dishwasher plug to hook up to the dishwasher: https://www.homedepot.com/p/Everbilt-5-ft-4-in-16-3-3-Wire-Dishwasher-Power-Cord-Kit-98250/307638974

  5. at this point we try plugging it into the free outlet (labeled “Dishwasher” on the outlet). This is a non-GFCI outlet. It did not work. We unplug the garbage disposal and plug the dishwasher in, and that works.

  6. so at this point, we’re thinking that something is wrong with the outlet, and we replace it with a GFCI 20 amp outlet. Plugged both devices in and nothing works. Or the few times that it did work, the circuit breaker would break, especially after we tried to turn off the disposal. Furthermore setting the circuit breakers back to ON, the circuit breakers for the devices produces a blue or red flash color (if that means anything to you guys) most of the time at the circuit breaker panel. We try with a 15 amp GFCI, same thing.

6a) We then put in a new plain old outlet plug (not the original since the original used an old wiring scheme where the wires were put into holes rather than the newer method of wrap around). That seemed to work again with one appliance but not both.

  1. we then tried plugging in a heavy duty extension cord coming from another outlet and then plugging in the appliances into this extension cord, and saw that the devices worked, so at least we knew it wasn’t the appliance itself.

  2. we then tried to replace the disposal toggle switch, thing that maybe that was defective. Didn’t help. But it did help in the sense that at this point in time, we plugged both units back into the new non-GFCI outlet, and the Dishwasher works, the garbage disposal works, but the on off switch does NOT work - if I turn on or off the switch, the circuit breaks for both devices. And this is where we are at. So for practical purposes, the garbage disposal is not functioning the way it should, although I can manually plug and unplug the disposal under the sink if I really wanted it to function.

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  • just to confirm, you actual wired the Plug for dishwasher ?
    – Traveler
    Sep 11, 2022 at 20:07
  • Usually if turning on a switch trips the circuit breaker, there is a hot/ground connection. A switched hot wire or screw is touching ground wire or box.
    – crip659
    Sep 11, 2022 at 20:07
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    @crip659 hot/ground connection always possible (been there, done that) but I suspect here a switched half MWBC combined with GFCI/receptacle with no way to handle two hots. Sep 11, 2022 at 20:36
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    Carl M, please clarify the sequence of events. Specifically, did you do anything to the receptacle (rewire, replace regular or replace GFCI) before plugging in the new dishwasher and before you had disposal problems? Sep 11, 2022 at 20:53
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    Please also provide pictures of how the GFCI is wired at present. You can edit to add those and the requested information.
    – Ecnerwal
    Sep 11, 2022 at 21:26

3 Answers 3

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First, since you are working on a rental unit, condo or multi-unit building, only a pro electrician can do the necessary wiring changes. Most AHJs will waive this for simple things like a dishwasher swap, or changing receptacles and lights. However in your case, things are a bit complicated, and beyond your skill level.

Some skill-ups

A "split receptacle" is the first skill you need to add to your repertoire. Commonly used in living rooms and bedrooms to avoid the cost of a ceiling fixture, this has the light switch control 1 socket on a 2-socket receptacle. This is also used to allow 1 receptacle to control both dishwasher and disposal. You need to know about it so you know it when you see it. GFCI receptacles cannot be split so they are incompatible with this setup.

I'm just giving you the search terms here; it's up to you to skill up.

The second concept is a lot harder: The Multi-Wire Branch Circuit or MWBC. This is where /3 cable is used from the breaker panel, to take 120V hot off 2 breakers (which should be handle-tied!) but sharing the neutral. This lets you carry 2 circuits' worth of power on one /3 cable. These must be wired carefully and correctly to avoid overloading the neutral (since the neutral is being used by both hot wires, they use a special trick to not overload it).

An MWBC can be delivered to a split receptacle.

Your legacy setup was a combination of all of the above. The MWBC is coming to a split receptacle, and, half the receptacle is switched for the disposal. This wiring allows the use of dishwashers and disposals too large to share a single circuit.

What to do

GFCI protection simply will not work in the way you're trying to make it work. You need to "roll it back" to exactly the way you found it with the split plain receptacle. I recommend reusing the original receptacle, otherwise you'll need to skill up on splitting receptacles. Make sure only white wires go on silver screws.

If you want to add GFCI protection here, you will need the services of a licensed electrician and possibly a permit pull (depending on what the work is). The far simplest answer is to replace the two single breakers (which are supposed to be handle-tied) with a 2-pole GFCI breaker - the AHJ will laugh if you ask to pull a permit for that "work".

Otherwise the 1-gang box containing your receptacle will need to be replaced with a 2-gang box to contain two GFCI receptacles - and many AHJs will want a permit for that. As such the GFCI breaker is probably the more elegant solution, and the receptacle will remain exactly as you found it.

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  • Forget the GFCI, it did not work before the OP installed it.
    – Traveler
    Sep 11, 2022 at 22:05
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    working on a rental unit Actually, not 100% clear. "have a condo" implies "owner occupied". "old tenant" implies "previous occupant was renting, so I'm renting too". So it could be owner or renter. Sep 11, 2022 at 22:06
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    @Ruskes sorry, you are mistaken. The split circuits are plainly described. The split receptacle is labeled for Pete's sake. If you actually read OP they'll say how they're trying to add a GFCI. Now it's possible the dishwasher-disposal outlet got flipped over so the markings are opposite, that would explain why the dishwasher outlet is "dead". It would be not dead if the disposal switch was turned on. Sep 12, 2022 at 4:26
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    @manassehkatz Doesn't matter if OP is tenant or landlord, the rule is the same. Doesn't matter if it's not even a rental unit if it's in a multi-unit building. Sep 12, 2022 at 4:28
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    Amazing how some people make bold statements that explicitly contradict very high reputation users with absolutely nothing to back those statements up, nor even any reasoning to support the contradictory comments.
    – FreeMan
    Sep 12, 2022 at 12:42
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TL;DR MWBC with split duplex receptacle, incompatible with a direct GFCI duplex receptacle replacement

Based on "share 2 15 Amp circuit breakers", I suspect you have a Multi-Wire Branch Circuit or MWBC. An MWBC takes a pair of breakers that are on opposite legs and puts them together. That lets you run 1 3-wire cable instead of 2 2-wire cables, which is a little cheaper (builders like that). There are a bunch of rules to do it right. In particular, the breakers should be next to each other but on opposite legs, so that the two hot wires have 240V between them but each has 120V to neutral. The easiest way to guarantee that is to make sure they are handle-tied or, even simpler, a double-breaker. (In case you think that is a trivial thing to make sure, in my recent heavy-up the electrician and I discovered an MWBC on one of the old fuse boxes that had the two hots on the same leg, which could have caused problems if I ever put large loads on that circuit.)

One neat trick with an MWBC is that you can run the 3 wires to a duplex receptacle, remove the tab connecting the two hots, and connect one hot to one hot screw and the other hot screw and the neutral to either neutral (they share if the neutral tab is not removed) and everything just works.

However, if you replace the duplex receptacle and do not remove the hot tab, then as soon as the two hots are connected they will short out flowing 240V with no load.

But there is a twist. If you did this with regular countertop receptacles, the problem would happen as soon as you connected everything and turned on the circuit breaker. However, with a disposal the hot wire is not actually connected to the receptacle until you flip the switch. And then it trips the circuit, exactly as you described.

Unfortunately, GFCI duplex receptacles do not let you split the two hots. That is for a few practical reasons, which are irrelevant here - just take my word for it.

There are a few solutions:

  • GFCI at the breaker. This is easy if your breaker panel is modern enough to accept GFCI breakers. But they (a) cost quite a bit and (b) are inconvenient to reset.

Based on updated information, it appears that the breaker is a GFCI/breaker. It may turn out to be AFCI, GFCI or both - waiting for more details. If it is GFCI or AFCI/GFCI then there is no need for GFCI/receptacle as the breaker provides full GFCI protection to all protected devices. And if that is the case, an ordinary duplex receptacle can be installed and should solve all the problems once it is installed correctly, which likely means removing the hot-side tab.

  • Split to a second receptacle. This, or a variant as described below, is probably the best choice. The bad news is that this is a bit of work. You will have to add a second box next to the first one. Split the neutral (pigtail). One box gets GFCI/receptacle for the dishwasher with its hot + a neutral. The other box gets GFCI/receptacle for the disposal with its hot + a neutral. Make sure to only connect to the LINE side of each GFCI, unless you have clearly marked "onward" wires. And if you do have such onward wires (microwave? kitchen lights?) then they go on LOAD, but only after getting the dishwasher and disposal working 100%.

Alternatives: Personally, I prefer hardwired dishwasher and disposal connections. Not a huge difference here, but just mentioning it. If you do that, you will use a GFCI/deadfront for each one. This looks like a GFCI/receptacle without the receptacle - it has the TEST/RESET buttons but nothing else. In this case, you have incoming power on LINE and hard-wired connections to dishwasher/disposal on LOAD. However, to do this correctly you need the right type of cable from each device to each box, which should be clearly detailed in the dishwasher manual and you should be able to find online in a manual for the disposal. But that is more work at this point in your situation since you already have a functioning cord/plug for each device.

There is one additional catch with the disposal. Some GFCIs don't like being switched. The worst case is a GFCI that requires a RESET after every power cycle. That is utterly incompatible with a disposal switch. Working through that to figure out how/where to wire a GFCI for the disposal will require more information, including pictures of the inside of the existing receptacle junction box and of the disposal switch box.

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It appears that before you started you had a split receptacle - bottom half switched for the disposal, top half unswitched for the dishwasher, each on its own breaker, probably an MWBC. There's nothing about that that would cause your described problem of itself, but there's also no way to replace that with a single GCFI that will work.

It sounds like you went right to replacing it with a single GFCI that won't work before attempting to use the dishwasher, and that is the cause of all your problems. How you even wired that to a GFCI is questionable in the extreme, but probably involves the opposite leg hot on the load terminal, so no wonder it trips when switched on.

Edit: OK, so you clarified that it wasn't working as originally wired, and then you chose to replace with an unsuitable GFCI (twice) without understanding how it should work, or checking that it could work, and then back to a regular outlet. We still need pictures of that wiring to offer better advice on what to try next, as opposed to guessing with only partial information. If power is actually getting to the outlet from both circuits, the common issue (since we must guess until this is clarified) here is that the tab between the hots needs to be broken, or it's a direct short between two hots that are 240V apart, when both are energized.

Given that a condo is a MDU (multiple dwelling unit) it's probably both best and perhaps the only legal route to call in a qualified licensed electrician to sort it out, rather than flailing further.

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    nothing to do with GFCI, or MWBC
    – Traveler
    Sep 12, 2022 at 2:29
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    Amazing how some people make bold statements that explicitly contradict very high reputation users with absolutely nothing to back those statements up, nor even any reasoning to support the contradictory comments.
    – FreeMan
    Sep 12, 2022 at 12:42
  • Amazing the lengths the USA goes to, just to make a 110V supply work like a 220V supply! Sep 12, 2022 at 16:58
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    That's 120V and 240V, and we have both available for different uses given the way things are arranged. Works fine if you understand what you are doing.
    – Ecnerwal
    Sep 12, 2022 at 17:00
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    This right here. youtube.com/watch?v=gZVx7GbAwlg Your earthing has compromises stacked until you have no way to safely install EV charging. We don't call things earth that are not earth, treat utility power as suspect, and do "TT" with locally bonded neutral. And this Just Works. We don't have those problems. Sep 12, 2022 at 18:56

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