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Original situation:

I have a 14/2 circuit, where the circuit powered 7 lights and 3 outlets. One of those outlets was in the kitchen and was powering a microwave and sometimes an air fryer. During microwave operation, the microwave sound started to sound lower in pitch occasionally suggesting to me that the circuit is overloaded or maybe that the microwave is going bad. I want to start at the circuit, because it is indeed underpowered for the microwave.

Appliance Usage

I usually use one or the other appliance, but not both. However, I might sometimes use both, but I imagine it will be rare, and so I don't know if it will be worth to wire up the circuit to account for using both, or using just one at a time. Also the way my appliances are positioned, both of them are plugged into the same kitchen outlet (the outlet in the photos).

Power stickers on the appliances:

  • Air Fryer: 1700W, 120 VAC, 60Hz
  • Microware: 60Hz, 11.5 amp, 120VAC

Note, however that when measuring amps directly the ammeter gave a reading of 16.4 amps at the highest for quite a while, and then it went down to 14 amp reading otherwise. I don't know if going from 11.5 amp to 14-16.4 amp is within the normal operating range of the microwave or if it is drawing more current because it is reaching its end of life or is faulty otherwise. I do plan to replace the microwave eventually.

Current Situation

I want to wire up a new outlet with duplex receptacles probably with 12 gauge wire that can handle both appliances. Chances are I will not run both of them at the same time, but there might be exceptions to where I do.

How do I best wire up this receptacle?

  • what AWG do I use?
  • what amp and type of breakers do I use, and where do I position them relative to each other?
  • what type of outlet do I use?
  • anything else I need to consider?

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dennismv
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    Most high-amp tools like power saws or appliances that generate heat like microwaves or hair dryers, etc. have bigger start-up (and often shut-down) amperage draw compared to normal running amperage, so that's normal. The rating stamped on the appliance is going to be the start-up/shut-down amperage, not the normal running amperage, if there is only one amp value listed (since that's the minimum needed to use it). – TylerH Jan 05 '22 at 20:05
  • AC power measurement is also very complex. For anything except the simplest resistive load, power factor comes into play - volt-amps aren't watts. Plug-in "kill-a-watt" style meters can measure power factor, but clamp meters cannot. – nobody Jan 06 '22 at 02:13

3 Answers3

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You've got a complicated issue here. You want to use a 20A circuit (which is required for new kitchen countertop circuits, so that is 100% correct) so 12 AWG wire. But you really want to be able to run two significant (> 10A) appliances at one time. You can't do that on a 20A circuit. There are two possible solutions:

  • MWBC = Multi-Wire Branch Circuit

    • Advantage: A little cheaper on wire, because you use one 12/3 cable instead of 2 12/2 cables.
    • Disadvantage: GFCI needs to be (practically speaking) at the breaker, which is more expensive than at the receptacle.

  • Two separate circuits.

    • Advantage: GFCI can be at the receptacle.
    • Disadvantage: Need two separate cables and two separate GFCI receptacles. (They can be in the same box side-by-side.)

An MWBC uses one neutral shared with two hots, together with a double-breaker (or two handle tied breakers, but double breaker is easier). The problem is that a shared neutral doesn't work well with ordinary GFCI receptacles, and a GFCI receptacle can't work with two hots anyway (you can't split it like a plain receptacle). But if you really want "a standard duplex receptacle with top and bottom each able to pull maximum current" then an MWBC is the way to do it.

Two separate circuits also uses two breaker spaces, but the breakers don't have to be next to each other. Each circuits needs GFCI but can use standard GFCI receptacles to do that. But you can't have the two receptacles of a duplex on two separate circuits unless you handle tie the breakers or use double breakers, and if you do that then you might as well save on cable by using 12/3 and then you have an MWBC.

Since you have easy access to run cables, I'd go with two separate 20A circuits, each with a standard 20A GFCI duplex receptacle. Mark one of them as "microwave". That way everyone knows "use the second receptacle of the duplex for small stuff like phone chargers but not for toaster or air fryer or other big stuff".

manassehkatz-Moving 2 Codidact
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    Why use a 20A receptacle? Neither device has a 20 A plug. – Glen Yates Jan 05 '22 at 20:01
  • 12/3 at my local big box stores is typically $0.25 more per foot if you go that way, or almost 2x as expensive if you get a pre-packaged 25ft roll. So depending on how long the run is, it's actually cheaper to go with two 12/2 runs. – TylerH Jan 05 '22 at 20:02
  • @GlenYates This (whether MWBC or two regular circuits) can use either 15A or 20A receptacles. Must be 20A *circuit* because of current code for kitchen circuits. OP included a picture showing they've already got a pack of 20A GFCIs. There should be *$ 0.00* or very close to no difference between the price of 15A and 20A receptacles of a given design (e.g., GFCI, regular or premium quality, etc.) because the only real difference is the T-slot. The internals have to be capable of 20A in either case, which is part of allowing 15A receptacles on 20A circuits. – manassehkatz-Moving 2 Codidact Jan 05 '22 at 20:06
  • Thanks! For the MWBC, will the shared neutral have to carry loads for both appliances? I understand that neutral is the wire that carries return current, so if both appliances are on, it may have to carry a load over 20-30 amps (?) - will that be safe? When using single pole breakers, does it matter if the breakers are in phase or out of phase on the panel? If I use a double-breaker, are they generally just as good as a single breaker - I.e. they have physically smaller switches, so I am questioning if they will have the same reliability, safety, and longevity. – dennismv Jan 05 '22 at 21:07
  • For your last paragraph - if I go with the two separate 20A circuits, with 20A GFCI each, I can have four receptacles total in the box (or across two boxes maybe if I decide to install an old work box alongside).... I understand that say I can mark the bottom receptacle of each to be microwave/air fryer and let the top ones be for charging. Did I understand that right? That seems like a good solution.... – dennismv Jan 05 '22 at 21:11
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    @TylerH on another forum, we recently determined that buying small rolls at Home Depot *is sheer madness*. One guy needed a 10' roll of 12/3. Home Depot would cheerfully sell 15' for $45. I was lectured sternly that it's every American's duty to shop at big-box for the savings, and we must run all those overpriced mom-n-pop hardware stores out of business "since they've been taken over by ACE". So I price-checked my local *very, very boutiquey* "Tiffany's" hardware store. 10' of 12/3 was $23, half of Home Depot's price. – Harper - Reinstate Monica Jan 05 '22 at 21:13
  • I gotta say I do like MWBC at least in theory even if I don't end up going that way. It seems that if I do go MWBC, I will probably use a standard non-GFCI receptacle and use GFCI breakers at the panel.. but before I do that I'd like to understand MWBC a little better. ... also I'd like to keep "the look" of the kitchen by keeping the GFCI receptacles like I have in the picture, so I will probably end up going that way, versus installing a different-looking outlet – dennismv Jan 05 '22 at 21:13
  • To clarify about MWBC: The keys are that (a) the two hots are on *different* legs/phases, each 120V to neutral but 240V to each other, (b) the neutral ends up with the *net difference* - i.e., if you put 15A on each hot, neutral shows*0A*, if you have 15A on one hot and nothing on the other, neutral shows 15A, etc., (c) breakers must be a true double or handle-tied, (d) breakers can **not** be two half-size breakers *except* inner or outer pair of a quad. You *can* do MWBC with two *separate* GFCI duplex receptacles, just wiring gets slightly confusing. – manassehkatz-Moving 2 Codidact Jan 05 '22 at 21:20
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    @dennismv with MWBC, you'll use GFCI breakER (singular) at the panel of the 2-pole/240V persuasion. About $80 pre-COVID. That's because GFCIs compare current on all wires to make sure all current that goes out comes back. – Harper - Reinstate Monica Jan 05 '22 at 21:20
  • Why would the OP need a handle-tied GFCI breaker to be able to run an MWBC here? What prevents running a MWBC off a standard handle-tied breaker with 2 GFCI outlets? – brhans Jan 05 '22 at 22:15
  • @brhans having only 1 gang-box available. Also note that on an MWBC you don't use 2 independent GFCIs handle-tied, it must be a 2-pole/240V GFCI. (due to neutral issues). – Harper - Reinstate Monica Jan 05 '22 at 22:22
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    @Harper-ReinstateMonica Sure, I agree with you; unfortunately not every town has a "Tiffany's"... but they do typically have a Lowes or Home Depot or Menards. Luckily I live in Southwire's global HQ town so I have access to a lot of high quality electrical stuff at pretty great prices. – TylerH Jan 05 '22 at 22:24
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    @manassehkatz, excellent answer, thank you! – dennismv Jan 06 '22 at 05:00
  • would you advise at all to put in a single-receptacle outlet, one for microwave, one for fryer just to avoid the possibility of plugging in extra appliances into the same outlet? Doing so seems reasonable to me, but also it will slightly change the look of the kitchen where most other outlets are the 20 amp GFCI... there are indeed pros and cons for everything – dennismv Jan 06 '22 at 06:40
  • by the way, using the 12/3 way with a shared neutral, will that create any issues, such as a looped neutral, or create more potential for neutral faults, i.e. if neutral gets damaged somewhere, I think that means that the next (single) appliance to get plugged into a receptacle will receive 240 volts, yes? – dennismv Jan 06 '22 at 23:02
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    If it is installed correctly, an MWBC with shared neutral will provide 120V to any device connected to one hot + neutral, will provide 240V (if desired) to any device connected to both hots, and will not have any problems unless there is damage. But damage will cause problems on **any** circuit. GFCI (required because Kitchen) will take care of most damage problems because it will detect imbalance between neutral and hots. – manassehkatz-Moving 2 Codidact Jan 06 '22 at 23:08
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Potential wiring faults

During microwave operation, the microwave sound started to sound lower in pitch occasionally suggesting to me that the circuit is overloaded

That's not how overloads work. Your circuit is probably short enough that it has <1% voltage drop at max amperage. If you overload it 200% (30A) then you have 2% voltage drop. A triple overload (45A) would only be 3% drop. None of that would even be detectable at the appliance.

If the appliance is struggling, either

  • a wiring fault is causing much worse voltage drop, meaning a connection is getting dangerously warm somewhere. Or
  • a house-wide Lost Neutral is causing big voltage swings. Lost neutrals are insidious; they can go months before displaying clear enough symptoms to identify them. Or
  • the appliance is dying.

Alien breakers

This is plainly a Siemens/Murray panel, noting the un-plated copper bus bars which are a signature.

Due to differences in bus bar spec, breakers not made for this panel should not be in this panel. The panel labeling lists all allowed breaker types, and I'm fairly sure GE THQL and Square D HOM are not on that list lol.

All modern 1" wide breakers will seem to fit each other's panels but won't engage to the bus bar properly, which can cause arcing and fire damage down the road. So the Square D and GE breakers (I assume there's an Eaton in there under a label, just to complete the collection) need to go and be replaced with Murray MP (now Siemens QP). We're talking $5 a breaker in normal pricing, so this won't break the bank.

Bringing enough power

I usually use one or the other appliance, but not both. However, I might sometimes use both, but I imagine it will be rare, and so I don't know if it will be worth to wire up the circuit to account for using both, or using just one at a time.

You CAN'T use both. I'd explain why (both appliances are over 10 amps) but you have the technical chops to know why.

This is true of almost all kitchen heat appliances, as almost all are 12 amps (they run at absolute limit of 1500W @ 125V rating).

If you are "unable to control yourself" LOL, then you could install a 1-socket receptacle (simplex) so you'd be forced to unplug one to use the other. However, my view is that we're the humans! Electricity is our servant not the other way 'round, and *electrical should Serve Our Needs. Therefore if you want to run both at once, why be limited? Run 2 circuits. Easy peasy. Copper is cheap.

Well, not right now. If I owned plenty of 12/2 but had to buy 12/3, I would run two individual circuits and double-split the receptacle (or change to a 2-gang box). A MWBC on 12/3 is alright, but will require a two-pole GFCI breaker (not two singles).

Note that if 2 separate circuits feed the same receptacle yoke, they must be handle-tied, or a 2-pole breaker. This is the one case where you can handle-tie two single GFCI breakers.

Note, however that when measuring amps directly the ammeter gave a reading of 16.4 amps at the highest for quite a while, and then it went down to 14 amp reading otherwise.

Because it is sharing the circuit with 3 other outlets and 7 lights. The extra 2-4 amps are coming from other lights or plug-in loads on the circuit, which are doing their own things.

Your questions

what AWG do I use?

You have no choice. Kitchen receptacles MUST be on 20A circuits.

So you must use 12 AWG copper (#10 if you have that).

#10 aluminum is also legal, but a lot of local inspectors will give you a fight on that.

what amp and type of breakers do I use, and where do I position them relative to each other?
what type of outlet do I use?

Kitchen counter receptacles require GFCI protection. That could be one 20A breaker and one GFCI repeptacle. Except that you have aspirations to run both appliances at once, which requires 2 circuits somehow. \

If you want to fit this into a 1-gang receptacle box, that means splitting the receptacle so each socket has a full 20A. (giving each a full 15A seems sensible, but is illegal per above). So these are our choices:

  • A 2-pole (240V), 20A GFCI breaker, feeding a MWBC (Multi-Wire Branch Circuit) via 12/3 cable. To a single receptacle with the hot side "split" and fed from each hot wire.
  • Two individual 20A GFCI breakers, with a handle-tie, placed adjacent since the handle-tie requires it. Dual 12/2 cable running to the receptacle. On the receptacle, both hot and neutral sides are "split". Each socket is powered from a separate cable.

If you are willing to blow out the box into a 2-gang box (or two 1-gang boxes), then you can use two GFCI receptacles, fed either from an MWBC or two independent circuits. In the latter case, the breakers can be anywhere. The MWBC breakers need to be handle-tied, so they will be adjacent. The cheapest way to get 2 handle-tied breakers is to use a 2-pole (240V) breaker.

Harper - Reinstate Monica
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    No comment on the alien invasion that has taken place in this panel?? – nobody Jan 06 '22 at 00:10
  • @nobody holy smoke yeah, I didn't spot that. – Harper - Reinstate Monica Jan 06 '22 at 01:57
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    The "alien invasion" is a good reason to _not_ put stickers over the breaker bodies like that. Is that actually allowed in code or is that verboten, too? – FreeMan Jan 06 '22 at 14:41
  • you've mentioned I can use 12 AWG, but #10 if I have it.... you mean 10 AWG? I don't have it but since I will be going through the troubles of installation ... should I use 10 AWG? It seems like it's not required, but why do you mention possibly using it? Will it give any significant benefit over using #12? – dennismv Jan 09 '22 at 20:39
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I would:

  • Put a 15A GFCI into the existing electric box
  • Install an old work box a few inches from the existing box
    • Just make sure it's in the same stud bay and you should be able to re-use the existing wire's chase-way

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Heck, go ahead and put in a double-gang old-work box and run two 12/2 wires to it so you can have two dedicated 20A GFCI outlets.

what AWG do I use?

I always run 12 AWG for outlets, period.

what amp and type of breakers do I use

The 14 AWG circuit can only use a 15A breaker, period.

The 12 AWG circuit can use either 15A or 20A breaker.

and where do I position them relative to each other?

It doesn't matter

what type of outlet do I use?

I believe the 15A circuit requires a 15A outlet as well. You don't want to put a 20A outlet on it and have people think it's a 20A circuit.

I recall some code that if there is only a single receptacle on a 20A breaker then it has to be a 20A receptacle. Multiple 15A receptacles can go on a 20A breaker.

Why does US Code not allow a 15A single receptacle on a 20A circuit?

anything else I need to consider?

Verify the circuit is off before touching wires =)

MonkeyZeus
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  • "*if there is only a single outlet on a 20A breaker then it has to be a 20A outlet.*" That's NEC 210.21(B)(1): "*A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.*" (note the word there is receptacle, not outlet) It isn't just for 20A but anything (there are special exceptions for a motor of less than 1/3 hp or an arc welder). Why this is the case was asked and answered in this DIY.SE thread: https://diy.stackexchange.com/q/210537 – TylerH Jan 05 '22 at 23:09
  • @TylerH Excellent! Added to my answer. – MonkeyZeus Jan 06 '22 at 16:40
  • question - why put a 15A GFCI into the existing electric box? I actually did have a 15A GFCI there, which I took out intending to convert it to a proper 20A GFCI, because I felt that 15amp was not a proper circuit for the appliances over 10A that I've been keeping & using there for a while. I also see in another answer that "kitchen receptacles MUST be on 20A circuit", which I understand must be due to the NEC. – dennismv Jan 06 '22 at 22:51
  • Ignoring NEC for a moment, I think a *dedicated* 15A circuit might work fine for each appliance in a real world application, but in my case almost half of all lights in my house are located on that 15A circuit, and plugging in a microwave in addition to that circuit is probably not advisable .... despite me having already done so for the last 10+ years, err. – dennismv Jan 06 '22 at 22:51
  • oh wait I think I am confusing 15A GFCI with 15A circuit. You are saying upgrade the circuit to 20A but use 15A GFCI ... I'm curious though, why use a 15A GFCI and not a 20A GFCI? – dennismv Jan 06 '22 at 22:55
  • @dennismv The existing circuit is 14/2 wire according to your pictures so 15A is the maximum allowed. – MonkeyZeus Jan 07 '22 at 01:45
  • @dennismv Are you still uncertain about anything? the 14/2 limits you to 15A maximum, period. In no way should you connect a new 12/2 wire to the 14/2 circuit and expect to be safe with a 20A breaker. – MonkeyZeus Jan 07 '22 at 16:30
  • Thanks, yes, 14/2 with 15A makes sense. My plan is to close out that 14/2 outlet, leave that wire unused, and instead pull a new 12 gauge wire and convert it to a 20A circuit, once I figure out which exact configuration I want. My reasons to do this mainly is to take the high-amp appliances off of that 14/2 circuit, and now I've also learned that kitchens should only have 20amp circuits. – dennismv Jan 07 '22 at 18:22
  • I think my confusion was that you said (or I imagined you said) to use a 20A circuit but put in a 15A receptacle, and I asked why not a 20A receptacle. It seems like they receptacles 15A or 20A are interchangeable nowadays, so maybe it is just a preference. I do like the look of a 20A receptacle, so if the circuit is 20A I will probably go for a 20A receptacle over a 15A one. – dennismv Jan 07 '22 at 18:30
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    @dennismv Nowhere in your post did you mention the desire to decommission the 14/2 wire so maybe I'm the confused one. Anyways. If you're going through the trouble of fishing new wire then I would run 2 wires so that you can have 2 dedicated outlets. – MonkeyZeus Jan 07 '22 at 18:58
  • Yes, sorry I never mentioned it just assumed perhaps that it will be ignored... I wanted to decommission it because it has most all of my houselights on it, and I didn't want it also have the microwave (a high amp device). Through this post I also see that this circuit is a good candidate to be decommissioned due to NEC rule of only having 20A circuits in the kitchen. And thanks I will pull two wires. That seems like a simplest least convoluted choice... Someone has also suggested to use 12-2-2 wire but I have not found one at a store just yet. – dennismv Jan 08 '22 at 01:55