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In my kitchen, there are 4 counter outlets. 3 are GFCI, one is normal. The normal outlet has a toaster oven, and one of the GFCI outlets has a microwave.

They are all on one circuit.

If I set the toaster oven to toast, and start the microwave cooking, the toaster will beep and turn off way too early. The toaster will also not keep consistent time on it's display.

The microwave is clearly causing some kind of surge that is affecting the toaster, so I was wondering if there is any way to add a circuit breaker to our box (there's two or three empty spaces). I can't seem to find good info on how to do this, and can't determine if it's something I can handle or need a pro for or if there's a better way.

It seems like it's not trivial.
 

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There's nothing really special about running a circuit to the kitchen vs other things, esp if it's an extra circuit vs designing the kitchen to be code-minimum. You want 20A for appliance circuits, and they should be dedicated. This way they will perform consistently wrt how many small appliances you can load onto them.

The only case where it's a fast fix is if the kitchen is right next to the panel (still not that fast), or if your kitchen is wired with 12/3 MWBC (multi-wired branch circuit -- incoming cable with red/black/white + ground) to all receptacles. That basically means both circuits are available in all receptacles. My house built in 1980 is that way. So it is possible to swap each receptacle between the two legs of the circuits, which each have 20A, with << 1 hour of work.

My brother's house built in 2013 has some MWBC in the panel but by the time it gets to the kitchen things are split off to individual legs to each receptacle.

As an alternative to running a new circuit you can run new wire from the other required appliance circuit (there are two minimum in the kitchen). However this requires you to trace wires, it's possibly easier to just do a new homerun from the panel, you don't have to trace anything when adding new stuff.

There are other fast hacks you can attempt like tapping off disposal or dishwasher but the performance will NOT be consistent with the regular receptacles so it may end in annoyance. And you need more electrical knowledge / code awareness to do this properly vs a new homerun circuit.
 

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If I set the toaster oven to toast, and start the microwave cooking, the toaster will beep and turn off way too early. The toaster will also not keep consistent time on it's display.
Go google the specs for that microwave and look at the amps. Now take the toaster over the sink and look at the electrical nameplate. Look at the amps.

Got those two numbers?

The microwave is clearly causing some kind of surge that is affecting the toaster, so I was wondering if there is any way to add a circuit breaker to our box (there's two or three empty spaces).
OK, go look at the circuit breaker. It has a number on the handle. 15 or 20. Those are amps.

Are you realizing something?


For this exact reason, NEC requires two 20A countertop receptacle circuits to a kitchen. NEC 90.1 "NEC is not a design guide or a best practice" - it is a slumlord bare minimum below which a home is considered uninhabitable.

What's more, if the microwave is "fixed in place" and not a countertop job, then it's required to not share those 2+ countertop circuits so it generally gets a circuit of its own. (potentially sharing with range hood or other small fixed-in-place loads).



Lastly, your kitchen wiring may be a "Multi-Wire Branch Circuit" or MWBC which is what Zanydroid is talking about. If so, the breaker will be odd - double-wide or half of a quadplex. In that case the handles should be tied so they throw together.

If that is the case, the surge could be explained by the entire house having a Lost Neutral. Since the house neutral is actually bonded to the ground rod, the neutral will try returning current through the ground rods through the dirt to other people's ground rods... and that will dampen the severity of the effects enough to make the effects subtle and bizarre. We had a Lost Neutral at my winter cottage (8 cottages sharing 100A service)... and it took us a week to realize it.

 
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