7

My Bosch micro/oven need 120 volt 20 Amp receptacle. I do not have a 20 Amp circuit breaker for this purpose. Can I couple two separate 15 Amp breakers as a dedicated source to provide higher Amperage limit (20 Amp)? Theoretically this will increase wire cross-section area for a higher Amp. limit. Is it permissible by code?

33

Paralleling is NOT Allowed

You can't do this (except under very limited circumstances that don't apply to your situation). The problem (ignoring the code violation) is that if one of those wires breaks (disconnected at any point between device and breaker) then all of the current will flow on one wire, which is not safe as it would put all 20A on one wire. If the wire that breaks is a neutral wire then things are even worse because then the breaker will never trip because it is protecting the hot wire with the assumption that the neutral will carry the same current as the hot wires. (In a 240V-only circuit, the neutral carries the difference between the hot wires - as little as "0", but in a 120V circuit it carries the same as the hot.)

You also must NOT simply replace the 15A breaker with a 20A breaker. Almost definitely the existing wire is 14 AWG, rated for 15A, and not 12 AWG (or larger) rated for 20A. So upsizing the breaker without upsizing the wire will also be a real fire hazard (and code violation).

The only real solution is to replace the wire and the breaker (i.e., a new circuit) or to find an oven that is rated to run on a 15A circuit.

  • 1
    I have encountered electrician that would do this, thinking "15A + 15A = 30A". Failure scenario is that you set your house on fire. You don't even need a full break. Corrosion will cause the current to shift to the other wire. – Nelson Aug 30 at 7:06
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    But if more than 15A shifts to the one wire, its 15A breaker should blow. I'm not saying it is safe (it sounds a horrible idea), but the explanation of why it is unsafe needs expansion. (One possibility is that the 15A breaker should blow, but might not. That problem also exists if a 15A appliance develops a fault. But in this case you know for sure you will be drawing 20A, whereas the chance of a 15A appliance developing a fault that draws enough to overload the cable but not enough to trip the breaker is smaller.) – armb Aug 30 at 10:39
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    Makes perfect sense as a physicist, actually. If you have a 20A rated wire, and it gets damaged (e.g. bent) to the point of only carrying 15A safely, the situation is comparable to the 15A+15A parallel wires example where you lose one wire. Except, the parallel situation is safe because one of the 15A fuses trips over a 20A current, whereas the damaged 20A wire will overheat as its 20A fuse does not trip. In fact, parallel wires are so safe that there's even intentionally manufactured. We call those braided wires. – MSalters Aug 31 at 23:26
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    As for the "if a neutral wire breaks", that should trigger two ground faults. And that leads me to the issue that I do foresee. With parallel wiring, how are you going to prevent ground faults in the normal situation? There's just no practical way to guarantee that the return currents exactly match the "respective" live currents. And yet the GFCI's are essential, precisely because a neutral wire might break. – MSalters Aug 31 at 23:31
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Absolutely not!

Circuit breakers don’t work like that. Did your microwave come with a plug that has 1 straight blade and 1 blade at 90 degrees? If so you will probably need a dedicated 20 amp circuit with #12 wire. 2 breakers depending on how located in the panel could provide 240v and if connected together “boom” If they could be paralleled they would not work correctly as breakers are inverse time devices. And as mentioned above if you have 15 amp breakers your wiring is probably only 14 gauge and 15 amp is the max breaker size. Large micro waves are one of the few devices that I have seen that require a 20 amp circuit so if the blades are not parallel 15 amp you will need a new circuit. To parallel wires they have to be 1/0 or larger, we do not parallel breakers.

  • Yes I have seen that and even a 240v model those are about the only normal appliances I can think of I have a deep fryer that is also 240 but it is a commercial model you don’t see those in homes very often. – Ed Beal Aug 30 at 17:29
5

The short answer is NO. Of course it might help to explain why.

"In theory" this would work as you expect (the part about increasing the wire cross section), but it's forbidden by code because there are a lot of dangerous issues related to this as well as practical ones.

You can't use two 15 amp breakers because that would still trip at 15 amps. You might be tempted to take two existing 15A circuits and connect them both to a 20A breaker, and that would "double" your wire size and work, but it's not safe. If there is just one bad connection somewhere (or a connection goes bad over time), the circuit would appear to work fine, but you would be pulling all that current over one wire instead of two which would overheat and potentially cause a fire. Even with all of that there's still the problem of trying to connect those two wires to devices that only expect one larger wire.

2

No, for reasons the other answers already address well. Moreover, rather than adding a circuit, it would be a lot less expensive and more useful just to replace the microwave with a normal 15A one. There's no need for high-wattage microwaves; to do anything other than heating water (cooking/reheating/thawing/etc.) you have to run them at lower power levels, which are usually just short duty cycle. A 50% duty cycle at 1000W is going to heat your food more evenly than a 25% duty cycle at 2000W.

1

Nope. You are not allowed to parallel conductors like that.

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    The op is asking about breakers, again absolutely not. Wires can be parallel if 1/0 or larger. – Ed Beal Aug 28 at 15:37
  • It takes more than that Ed, it also requires special equipment at the source rated for paralleling. You can't just run six 1/0 conductors 190' out to your shed and punch four of them down on any old 100A breakers and call it a 200A feeder. Becuase stock panels are not rated for paralleling. – Harper - Reinstate Monica Aug 28 at 16:28
  • But you can pigtail as long as the conductor length and terminations are the same on both or all 3 it is that easy I do it all the time double triple and quad lug breakers are quite common with larger sizes in fact it is more common to parallel than run huge wires. – Ed Beal Aug 28 at 17:47
0

Sounds workable in theory, but...

As already stated in other answers, it would be a code violation because it would be unsafe; electrical codes exist for good reason.

Going beyond safety issues, there are all sorts of reasons why this just isn't a workable idea.

Most kitchen outlet boxes are wired with two "hot" lines so that top and bottom outlets can each serve up to a 15A load, for 30A total at 120V right? WRONG! The two hot lines are on opposite phases; between them you actually have 15A capacity at 240V. Yes you normally use them as if it was 30A worth of 120V, but that's not what is actually going on, so you can't simply join them in the outlet box. If you attempted to join them in the breaker panel (VERY BAD IDEA) you'd theoretically have 30A capacity on the hot lines, but only 15A capacity on the one neutral feeding the box (all sorts of unsafe/bad/fire hazard). If you tried to gang up power from other outlets, you might as well just run a new 20A circuit.

As already stated, your only two options are:

  1. Exchange the appliance for one which can operate on a 15A circuit, or
  2. Run a proper 20A circuit to feed your microwave.

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