circuit amps for microwave and ac

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  #1  
Old 07-29-15, 02:44 PM
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circuit amps for microwave and ac

Is 20 amps enough for a 1100 watt countertop microwave and a 8000 btu 7amp window ac unit?

We have had a 1000 watt microwave on that circuit with the window ac for a year now and the microwave over heated and shut off yesterday. The fuse box did not flip though and have never had it flip. I think the microwave just failed on it's own since the room it's in is almost 90 degrees.

Anyways, it got me thinking whether I'm over loading this circuit and maybe I should get a smaller microwave. What do you think?
 
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Old 07-29-15, 02:49 PM
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Although the MW can share one of the 20 amp small appliance countertop circuits, it is better for it to have a dedicated circuit. The AC cannot be on the counter top circuit.
 
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Old 07-29-15, 03:02 PM
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Is that a general rule or mine is over loaded? It's an energy star ac unit and we've never had it's circuit trip or the fuse box.
 
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Old 07-29-15, 04:14 PM
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Lived in a very old apartment with a 30a service. Made the mistake of turning on the microwave while the washing machine was running. The voltage drop apparently increased the amperage enough to blow the fuse in the microwave. That may be the problem (or it may not). Wattage is a product of amps times volts so a voltage drop increases amperage.
 
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Old 07-29-15, 04:35 PM
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I'm thinking of getting a 900 watt microwave. The ac unit is 740 watts. 740+900 is 1640watts and a total of about 15 amps between the two. That should be ok right?
 
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Old 07-29-15, 05:50 PM
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That should be ok right?
It sounds like you don't have a choice so it will have to do.
What happened to the 20A circuit they were on.

The problems occur when the microwave is running and the A/C compressor come on at the same time.
 
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Old 07-29-15, 06:02 PM
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They are on a 20 amp circuit... The 15 amps I mentioned are the appliances' listed load.
 
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Old 07-29-15, 06:16 PM
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The compressor draws three times or more FLA when it starts.
 

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Old 07-29-15, 06:31 PM
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FLA? Not sure I understand what you mean. The ac unit says 7amps. Are you saying it's 21amps when the compressor starts?
 
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Old 07-29-15, 08:01 PM
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FLA=Full Load Amps.
Are you saying it's 21amps when the compressor starts?
Or more.
 
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Old 07-29-15, 08:21 PM
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How can one be sure that the 7amps on the name plate isn't the FLA? It seems they are misleading.
 
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Old 07-29-15, 08:41 PM
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The running amps are listed on the nameplates. It is not misleading as the unit does not draw the startup current but for a very short period.
 
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Old 07-30-15, 10:58 AM
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It is what it is. The safest thing to do without running new circuits would be to turn off the A-C when you run the microwave.
 
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Old 07-30-15, 11:50 AM
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The amps are also listed for nominal voltage. Both the AC and the microwave are inductive loads, which means the amps they draw goes up when the voltage dips down. A circuit loaded near its upper limit has a drop in voltage, causing the appliances to draw more amps, causing a bigger drop in voltage,..., and the cycle can continue until the breaker trips. Joe's suggestion is probably the best in this case, flip off the AC until the hot pocket is done.
 
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