Best Practice - for Microwave

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Old 09-04-15, 12:13 PM
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Best Practice - for Microwave

The house we recently bought has a 20 amp circuit labeled MICROWAVE.

There are a total of 3 outlets on this 20 amp circuit.

The circuit appears to feed (in this order) 1) a 15 AMP GFCI outlet, the LOAD on this 1st outlet feeds load 2) the microwave in the upper cabinet, which is a 20 amp outlet the microwave is plugged into. The Microwave outlet feeds the final 20 amp outlet.

I have read that a microwave is SUPPOSED to have its own 20 amp circuit. Since I often plug a toaster in to the outlet coming out of the microwave outlet, would this exceed the safe usage?

I often wondered why the previous home owner installed 20 amp circuit for just 2 outlets, not thinking the hidden microwave outlet was also in the same circuit. I thought perhaps they used heavy mixers, etc.

It sounds like I will either be 1) moving the feed to the microwave leg to the non gfi side of the 1st outlet, and installing a gfi outlet on the 3rd and final outlet, or 2) running a new, dedicated non GFI 20 amp circuit to the microwave, leaving just 2 outlets on a 20 amp circuit. I can easily plug the toaster into a different outlet, which is a different circuit.

Can I safely keep this configuration, knowing I need to relocate the microwave off the GFI load side, and not use heavy draw items if Microwave is in use?


I appreciate your expert thoughts and recommendations,

Thanks
 
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Old 09-04-15, 12:25 PM
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I can't speak to the code issues. But I would think if the wiring is apt for a 20amp circut, the most you could do is fry an appliance and even that would require them both being on at the same time. How many watts does the toaster draw, how many does the microwave? That info should be listed on them somewhere.
 
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Old 09-04-15, 12:26 PM
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I have read that a microwave is SUPPOSED to have its own 20 amp circuit.
Not specifically. That applies to the 50% rule for fixed in place appliance. If a microwave is part of an exhaust hood it is fixed in place. If it just sets on the counter top it isn't. There is no rule for microwaves that set on the counter top.

If it is fixed in place the rule reads if the total amps used is more then 50% of the circuit capacity there can be no other devices on the circuit. Informally though most electricians will just put a fixed in place MW on a dedicated circuit regardless of if it will exceed 50%.
 
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Old 09-04-15, 12:32 PM
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Built-in microwave ovens over the range require a 20A circuit by code. Other built-in microwaves would require a 15A or 20A circuit depending on the manufacturer's instructions. A countertop microwave can be plugged in to standard countertop receptacles which in a newer house will be 20A, but my be 15A in older houses.
 
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Old 09-04-15, 12:37 PM
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2600 watts if both used at same time

So, the Microwave uses 1,100 Watts, and the toaster uses 1,500. I wonder how this passed code inspection during their re-model...

I can run a new dedicated circuit fairly easily, sounds like the way to go?
 
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Old 09-04-15, 12:41 PM
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Code only requires that kitchens have at least two 20A circuit serving the countertop receptacles to meet code. Older homes may only have a single circuit or 15A circuits instead of 20A. What gets plugged in to those circuits is up to the homeowner.

If you do choose to run a new circuit, it must be 20A; but yes if you have access to an open attic, basement or crawlspace it should be pretty easy to get a new circuit into the kitchen.
 
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Old 09-04-15, 01:07 PM
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And just two minutes ago, I discovered a 20 amp outlet, behind a book case on the other side of the microwave (never used by our family) but should that cabinet ever get moved and used, it would push the limits.

Thanks all, for the advice..
 
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Old 09-04-15, 01:31 PM
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1100W and 1500w are max draw, which is 23 amps if both were drawing the maximum current at the same time.

If that happened you're going to trip the breaker. The reason the breaker is there is to prevent damage to the wires and outlets (which are rated at more than 20 amps). If the breaker isn't tripping, you're not overloading the circuit. If you're not over loading the circuit I think you might be trying to solve a problem you don't have.
 
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Old 09-04-15, 01:37 PM
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I agree with that logic, and if I keep it , a re you of the opinion I should then move the microwave outlet from the load side of the GFI outlet?
 
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Old 09-04-15, 01:53 PM
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Breakers are not a binary device. They are designed to operate within some tolerance with accommodation for brief overloads. Circuits are also designed with adequate margins to accommodate brief, mild overloads. A breaker at 110% capacity may take an hour or more of continuous load to trip if it ever does. A breaker at 200% overload might trip in a few seconds, and a breaker at multiple times its rating will trip in milliseconds.
 
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Old 09-04-15, 01:56 PM
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The receptacle should remain on the load side of the GFI receptacle. The ampacity of a circuit is determined by the breaker size and wiring.
 
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Old 09-04-15, 02:01 PM
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A typical trip curve for a residential 20A breaker shows that at 40 amps load, it may take from 10 to 50 seconds to trip off. At 23A, it might not trip for a half hour, maybe not ever.

http://static.schneider-electric.us/...CT9801R108.pdf

I'm not seeing a problem here, and I would not change any wiring.
 
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Old 09-04-15, 10:43 PM
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The microwave above the stove calls for a dedicated circuit per the instructions that apparently were ignored. Since it is easy, add a new circuit for the MW.
 
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Old 09-05-15, 06:04 AM
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Microwave

Have we established that the microwave is built in? Or is it free-standing in a cabinet?
 
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