How many watts can be running on a 20 amp household circuit?

Question

I have a microwave (1600w), toaster oven (1200w) and coffee maker (1000w) each plugged into a different recepticle but all on the same circuit. It's possible that they will all be running at the same time for a few minutes. I tried it and it didn't trip the breaker. But is this 3800w total too much? If you divide 3800w by 120v you get 32 amps but I'm not sure this is a correct calculation for AC power.

Answer 1

A 20A breaker should only carry 2400W continuously. However we should only size the load for the circuit to run 80% continuously or 1920W.

However most breakers do not trip instantaneously when they reach 20A. Most are thermal magnetic. This means that for a low value fault such at 30 or 40 amps the thermal portion of the breaker comes into effect and eventually trips the breaker due to heat. If a hard fault of a few hundred amps occurs the magnetic portion of the breaker will trip instantaneously.

Breakers are set up this way to allow for momentary overloads and to allow for motor starting. When motors start they draw about 6 times as much current as they do when running. If you had a motor that ran at 12A it would run fine on a 20A breaker. But if this was an instantaneous breaker as soon as you tried to start it the motor inrush would be about 72A and the breaker would trip. A thermal magnetic breaker would run just fine and let the motor start.

Part of my job as an Electrical Engineer involves selection of the right overcurrent device to properly protect equipment. One of the things you must also do is properly coordinate the breaker protecting your equipment to the breaker thats protecting the whole panel and then coordinate it to the breaker feeding the panel then coordinate it to the breaker feeding the substation and on and on back to the generators.

To do this manufacturers provide breaker (and fuse) trip curves that show the time-current characteristic of a breaker. After you obtain all these curves you must select the proper settings that will protect the equipment and keep from tripping out things higher up the chain.

Here is an example of a time current curve for a breaker.

http://www.dotznize.com/electric/images_a/cb_curve.gif

This is probably not the curve that your breaker uses but will give you an idea of whats happening.

If your running 32A on a 20A breaker your running 160% of your breakers limit and using this curve you can see this breaker would trip in a little under a minute. Your breakers curve could be a little different and allow the 32A to run for a longer amount of time before tripping. You also could be running under 32A as voltage variations will affect the power output as well as current.

In the end its nothing really to worry about. All those appliances shouldn't be on the same circuit and the circuit is overloaded, but there is certainly nothing wrong with your breaker. The breaker is operating as it should.

Hope this helps!

Answer 2

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RE:
How many watts can be running on a 20 amp household circuit?
I have a microwave (1600w), toaster oven (1200w) and coffee maker (1000w) each plugged into a different recepticle but all on the same circuit. It's possible that they will all be running at the same time for a few minutes. I tried it and it didn't trip the breaker. But is this 3800w total...

Answer 3

20 Amps To Watts

Answer 4

The bottom line is that you have an over loaded circuit. Yes you are calculating the the current correctly. In spite of the fact that the breaker does not open (for whatever reason) in all likely hood the wiring is rated for 20 amps. Keep overloading the wiring and you are asking for overheated wiring with he potential of starting a fire. Stop using the appliances at the same time or bring in some properly sized circuits.

Answer 5

volts X amps = watts is the formula
so a 20 amp breaker on a standard 110 volt feed can handle 2200 watts before it trips. You rarely have all those appliances on at the same time, but if you do it will trip the breaker. Your micro should have its own breaker anyway. Just like your fridge dishwasher, and washer do.

Answer 6

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Answer 7

formula= VOLTSXAMPS=WATTS
i.e.- 120volts x 20amps = 2,400watts
you should only load any circuit to 80%. thus.
2,400watts x 0.80 =1,920watts max. this circuit should be loaded at any given time.
it would be best if you can plug something in elsewhere, if not, i might suggest you add another circuit.
hope this clears things up for you. good luck.

Answer 8

The wattage rating of most appliances is deceptive. It is the MAXIMUM that the appliance will use.
This max can occur at any point in the cycle. The way to see how much power an appliance uses it to measure the power with a monitor. Another way is to write to the manufacturer and ask what the maximum is and when that occurs.

Answer 9

Doesn't matter what the formula says, things are wired differently. You need to find out how many amps each of your appliances draw to be sure. It should say on the little sticker on the back, or on the plate (usually on back) that has model #, etc...