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I have very very limited electrical knowledge, however I love learning and am interested in electrical as well.

Thus, the question: I have an over-the-range microwave that trips its breaker (where the fridge is also connected) whenever my family uses it. It fixed itself for awhile and now it's doing it again. We rent, so we asked the "handyman" that fixes things in the apartment complex and he said we should try to not use many appliances at the same time (he said the oven mainly -on a different breaker, but he didn't mention that-).

My question for everyone is: does that make sense? I was under the impression that each breaker is its own circuit and should be independent of each other.

Barring the obvious reasonings of: "the microwave having to be replaced" and "there might be faulty wiring" (wouldn't put it past the complex), would there be an issue with the panel?

Thanks!

Hect'
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    Does the breaker trip *instantly* when the microwave is turned on (use a mug of water as a dummy load when testing!) or after a period of time? Does it get warm/hot when it trips? Does the breaker have a TEST button on it? – ThreePhaseEel Aug 29 '23 at 11:49
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    Yes, please revise to better describe the failure mode. – isherwood Aug 29 '23 at 19:11

4 Answers4

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There are 3 different types of possible breaker trips. The solution will vary depending on the type of breaker trip.

  • Overcurrent

This is simply "too much stuff running at the same time on one circuit". This should rarely happen in a properly wired kitchen. However, many older kitchens were wired under older versions of the NEC, and before modern appliances such as microwave ovens. A typical microwave oven may use 1200 watts of power when running. If it is on a 20A circuit (the standard these days) then that is only about 1/2 the circuit capacity. If it is on a 15A circuit then that is about 2/3 of the circuit capacity. A refrigerator may use 500 watts or more, so the total can easily exceed the capacity of a 15A circuit, particularly if there are other devices on the same circuit.

The solution to this is to put the microwave oven or the refrigerator on a dedicated circuit. There is a different rationale for each one: Putting the microwave oven on a dedicated circuit makes sense because it uses 1/2 (possibly more) of a full circuit, leaving relatively little capacity for other things. A refrigerator typically uses far less than 1/2 of a circuit's capacity, but it is very important that it always be running, and a dedicated circuit means other things (like your microwave) won't stop the refrigerator.

The problem is that adding a circuit can be anywhere from cheap and easy (space in the breaker panel and a short run from the panel to the kitchen) to expensive and hard (no space in the breaker panel and/or a long distance from the panel to the kitchen).

  • GFCI - Ground Fault Circuit Interrupter

This is a device which protects people from certain types of electrical problems that can kill them. It is a very important safety feature around water, so it is now required for most circuits in a kitchen. However, an old refrigerator can have certain types of problems that result in a GFCI tripping but which don't present a real danger to people. In addition, a legitimate GFCI trip (which may be happening with your microwave, for example) might be unnoticed, leading to a refrigerator stopping and spoiling food.

  • AFCI - Arc Fault Circuit Interrupter

Arc faults are more of a fire danger than a direct life safety issue. Large appliances (both microwaves and refrigerators) could trip an AFCI under some circumstances where there isn't a true/dangerous actual arc fault.

The first step is to figure out what type of breaker trip you have. If the breaker has a TEST or RESET button or any indicator lights on it then it is most likely a GFCI, AFCI or both. If it does not have any buttons or lights then it is most likely only an overcurrent breaker. If it is a GFCI or AFCI breaker then the next time it trips you need to figure out which type of problem caused the trip. The method of figuring that out varies by breaker brand, but we can help if you upload a picture of the breaker.

Overcurrent can really only be fixed with new circuits, but the usual workaround is to move things so that there isn't too much stuff on any one circuit. If you can do that without extension cords, great. If you can't do that without using extension cords then your landlord should provide a fix - generally a new circuit.

GFCI and AFCI are indications of actual problems. They should not be ignored. If a microwave oven causes frequent GFCI or AFCI trips then that is an indication that it is faulty and should be replaced.

manassehkatz-Moving 2 Codidact
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I had the exact same situation as you. Fridge and microwave connected to different outlets but they were likely wired to the same breaker. I informed the landlord who reset the breakers and it happened again randomly. He then asked that i put the microwave to a different outlet which i obliged and never had a further issue.

Not as detailed as Macguffin's post but just sharing my own experience.

Eric
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While local building code can vary nearly every jurisdiction in the USA (and I'm assuming this is the USA) will use the same national and international codes as a baseline. Part of those codes (as I recall anyway) requires the microwave and refrigerator on separate circuit breakers to address the very situation you are seeing. Not only are they to be separate from each other but separate from all other electrical outlets in the kitchen.

Again, there may be local variation or exception but this looks like a building code violation and the "handyman" should not be so flippant about your complaint. Assuming there is no building code violation (such as a "grandfather rule" allowing old buildings to remain in compliance) then a new circuit breaker might solve the problem. I don't mean swapping a 15 amp breaker for a 20 amp one (I've seen that happen) but a new breaker that hasn't seen as much wear. The wear on the breaker could make it trip with a lower level of current than is in the original spec.

The conventional oven will be on it's own circuit breaker (and if not then I suggest finding a new apartment because that's a serious building code violation) so will have no impact on the microwave oven. If the main panel breaker is tripping from the microwave oven then there might be something to say about an electrical panel problem with the conventional oven.

I'd suggest at least looking into making some kind of complaint to whatever local authority oversees property rentals. Your complaint alone is not likely to do much but if the same "handyman" has enough complaints filed then expect to see a more attentive attitude from him.

MacGuffin
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  • Can I have a section number for your IPMC citation please? I'm not finding where it's requiring that... – ThreePhaseEel Aug 29 '23 at 11:48
  • I can't find it right now either so I edited my answer to remove reference to IPMC. I recall there's electrical code somewhere requiring dedicated circuits to a refrigerator and permanently installed microwave, I just don't recall where. This has come up several times during inspections, new builds, and remodeling, and I just saw that code somewhere in the last week or so. I got the wrong acronym, if its not IPMC then ICC, IRC, NEC, something ending in "C". – MacGuffin Aug 29 '23 at 14:44
  • *Citation needed*. Generally speaking, dedicated circuits are required for any permanent 240V appliances (e.g., cooktop even if only 20A), any appliances > 20A (which is mostly going to be 240V as well, because otherwise you go with a 240V 15A or 20A instead of 120V 30A or 40A, *mostly*) any any hardwired appliance that uses > 50% of a circuit. (Actually, even that last one *can* have other stuff, but must all be hardwired - e.g., lights together with a disposal.) So a countertop microwave will ideally have a dedicated circuit but it is **not** required. An over-the-range microwave is where it – manassehkatz-Moving 2 Codidact Aug 29 '23 at 15:49
  • gets a little fuzzier, because while it is not hardwired it is effectively permanently installed, so arguably it *should* have a dedicated circuit. But a refrigerator? Except for the "here is how we circumvent GFCI requirement" idea (which is becoming less plausible as GFCI requirements increase) there really isn't much need for that because a typical residential refrigerator uses less than 50% of a circuit when actively cooling and much, much less when in standby ("off" part of the cycle). – manassehkatz-Moving 2 Codidact Aug 29 '23 at 15:50
  • "Citation needed." My point is that it is very common to see local building code require the refrigerator be on a dedicated circuit, so if a rental property doesn't have this then it is likely a violation of code. Check your local codes since YMMV. This is not because refrigerators are large loads but because if something else trips a breaker it's not removing power from the refrigerator in the process. Spoiled food is bad so building codes take that seriously. – MacGuffin Aug 29 '23 at 16:00
  • "An over-the-range microwave is where it gets a little fuzzier, because while it is not hardwired it is effectively permanently installed, so arguably it should have a dedicated circuit." It's not so fuzzy in my experience, check your local building code and I'd bet with 100 to 1 odds that an over the range microwave is specified to have a dedicated circuit. This would be on top of the typical two separate circuits for countertop appliances, and perhaps another for things like a garbage disposer and dishwasher. – MacGuffin Aug 29 '23 at 16:11
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    *What is a good idea* and *what is enshrined as code* are quite often two different things. Quite a number of us are very familiar with what the NEC (NFPA70) requires of kitchen circuits. Dedicated refrigeration outlet is not one of them. And so long as that does not directly kill people or set houses on fire, I would not expect it to be. It's still a good idea, but it's not code. – Ecnerwal Aug 29 '23 at 17:22
  • I don't think this is in NEC. I'd be interested to see any local (city/county/state) code that has these requirements. There are all kinds of local amendments out there, and I do think these are *plausible* requirements. But I wonder whether they actually exist in the wild. As far as "then it is likely a violation" - well, an awful lot of rental housing is older and therefore not subject to modern codes with certain exceptions (e.g., smoke detector requirements). So current code (which is important, citation needed) is not the same as "likely a violation" if the rental property is decades old. – manassehkatz-Moving 2 Codidact Aug 29 '23 at 18:30
  • "What is a good idea and what is enshrined as code are quite often two different things." I absolutely agree. I've seen building codes require a dedicated circuit for a refrigerator, and I suspect jurisdictions local to me aren't all that unusual to the rest of the USA. I could see how a required dedicated circuit for a microwave could get "fuzzy" as it is fairly trivial to have a typical range hood replaced with a microwave hood, or what was a cabinet converted to a microwave oven "cubbyhole". Whatever the case I'm suggesting a check of building code as "leverage" on getting a fix. – MacGuffin Aug 29 '23 at 18:45
  • Here's at least a hint that NEC requires a dedicated circuit, and it is 5 years old: https://www.howtolookatahouse.com/Blog/Entries/2018/12/is-a-refrigerator-required-to-have-its-own-dedicated-circuit.html – MacGuffin Aug 29 '23 at 18:49
  • @MacGuffin -- recent NECs all permit refrigerators to be on a SABC. a dedicated fridge circuit is also *permitted*, but not *required* – ThreePhaseEel Aug 30 '23 at 02:02
  • I'm still seeing people miss the point. It is exceedingly unlikely for local building code to allow the refrigerator and over-th-range microwave to share a circuit breaker. This is because nearly every jurisdiction will take NEC or some similar code as a baseline and make amendments above those recommendations. According to one answer posted earlier there's a half dozen points in NEC which could specify why the microwave and/or refrigerator should be on separate breakers. https://diy.stackexchange.com/questions/110863/over-the-range-microwave-on-small-appliance-branch-circuit/229148#229148 – MacGuffin Aug 30 '23 at 04:50
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I had the same problem with an AC unit and new nothing about electrical either. Luckily I had a neighbor explain it to me this way and haven't had a problem since. As previously stated in another answer, wiring in a new dedicated circuit breaker is best. But if there isn't the space in your box to do that, you might try increasing the amperage of the breaker the microwave is on. Increasing a breakers electrical intake can only be done if the numbers on the breakers when added together is at or less than 110. Every house is wired for appliances that use 110 or in some cases 220 for some air conditioners. If you're house is using 110 that is the amount you have to work with. If your breakers for instance have one that is 15 amp, another 25 amp, and a 30 amp your total amps available inside for you to use would be 70. That would leave you able to increase the breakers by 30 amps. This could be on just one breaker or spread out over them all. Your choice, but I wouldn't exceed 100 amps and leave the 10 extra just for safety and wiggle room, unless you are able to measure the incoming voltage, then you'd know exactly what you have to work with and use the whole 110.

Colleen Brennan
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    This is a **TOTAL ABSOLUTE DISASTER WAITING TO HAPPEN**. You are mixing up amps and volts. Even if 110A was your service feed, adding the breaker handles has very little to do with it - you can easily have numbers on breakers that add up to far more than the service feed size and still be safe. But you should **NOT EVER** increase the size of an individual breaker unless you are 100% certain that the **WIRES** are sized appropriately. That can happen *sometimes* - e.g., a circuit with 12 AWG wire that was breakered at 15A can be increased to 20A. But it is relatively rare. **DON'T DO THIS**. – manassehkatz-Moving 2 Codidact Sep 03 '23 at 01:06