microwave on GFCI?

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Old 03-23-07, 07:55 AM
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microwave on GFCI?

Can I run a microwave (over the range unit with fan and light) on a GFCI protected circuit?
 
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Old 03-23-07, 08:03 AM
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Yes, on a new one, but not on one of the ones already in your kitchen.
 
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Old 03-23-07, 08:12 AM
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What John is telling you is that your microwave can run on a GFCI protected circuit. The GFCI will not bother the microwave at all. However, you cannot simply extend one of the counter top circuits up and use it to provide power for the microwave. An over the range microwave needs a dedicated circuit. Often this is stated in the documentation for the microwave, but even if it's not stated it's still a necessity.
 
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Old 03-23-07, 08:26 AM
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Is that a code requirement or a reccomendation? Or in other words what is the rationale? I ran the numbers and it doesn't really draw that much power.
 
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Old 03-23-07, 08:33 AM
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It's an absolute firm requirement.
 
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Old 03-23-07, 08:36 AM
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The counter top circuits cannot serve the range hood or a microwave installed there. You wouldn't want this even if it were allowed.

Whether a dedicated circuit is required or not depends on the unit. If the instructions stipulate a dedicated circuit then a dedicated circuit is required. If the unit draws enough power then a dedicated circuit is required.

Regardless of what might or might not be required by code (and it most likely IS required by code), you want an over the range microwave oven on a dedicated circuit.
 
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Old 03-23-07, 09:27 AM
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Microwave ovens draw a lot of power while they're running- 12A+, usually. By NEC, it needs a dedicated receptacle. For new construction, this is always enforced.

Are you replacing an existing range vent/hood? If so, is it coming off the kitchen lighting circuit? What else is on that lighting circuit, how many watts of light fixtures? If this is the case, strictly speaking, it still requires a dedicated circuit, but you could ask your inspector if you can just re-use the existing hood connection, they might be lenient. (Or they might not.)

Honestly, I never quite understood the rule that says it's OK to sit a microwave on the counter and plug it into a kitchen GFCI, but OMG, it's illegal if you mount that microwave to the wall! I guess it boils down to practicality- tough to require dedicated microwave and coffee pot receptacles if you don't know when they're mobile and you don't know where they're going to be. BUT, that's why kitchens need 2 strings now! Small kitchen appliances can draw a LOT more power than most laymen realize.
 
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Old 03-23-07, 10:07 AM
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> I ran the numbers and it doesn't really draw that much power.

You can't use the "cooking watts" number to calculate how much power the appliance uses. The cooking watts does not include the energy loss in the magnatron circuit, fan motors, lights and control circuitry. The actual power draw is usually a few hundred watts higher than cooking power.

Install a dedicated circuit for the microwave-hood.
 
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Old 03-23-07, 10:11 AM
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Just to clarify, and this has already been covered, but you cannot use one of the existing countertop circuits, even if for some reason your microwave does not require a dedicated circuit.

As ibpooks says, the input power and the output power of a microwave can be quite different numbers.
 
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Old 03-23-07, 11:31 AM
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If it is “over the range” and it has a plug, section 422.16(B)(4) line (5) requires it be supplied by an individual branch circuit.
 
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Old 03-23-07, 11:33 AM
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Not that it matters since It's already been covered,The previous owner had installed no fewer than 4 seperate dedicated 20A single outlet circuits, to serve the kitchen countertops/island.

My intent was to extend one of those circuits to run the microwave. Which would leave 3 dedicated 20A small appliance circuits and one that has a countertop outlet and also serves the microwave.

Yeah I guess my thinking was like grover mentioned--the previous owner had a plug in microwave, I'm not really changing that, I'm just mounting it on the wall.

I understand your advice though.
 
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Old 03-23-07, 11:39 AM
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You cannot extend one of these four circuits, but you might be able to convert one of them is you remove all the other outlets on that circuit, putting them on other circuits instead.
 
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Old 03-23-07, 12:10 PM
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Originally Posted by Juhl View Post
If it is “over the range” and it has a plug, section 422.16(B)(4) line (5) requires it be supplied by an individual branch circuit.
Isn't that crazy? I checked it out and it appears this requirement is only if it has a "flexible cord and plug." So if it were direct wired it would not need a dedicated circuit?

You guys have alot more patience than me if you deal with these code requirements all the time.

Thanks for all your help!
 
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Old 03-23-07, 12:52 PM
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> So if it were direct wired it would not need a dedicated circuit?

If it was hardwired, then different rules would apply. The microwave would require a dedicated circuit if its power consumption exceeded 50% of the circuit. Most all microwave-hoods draw at least 10A (50%) and less than 16A (80%) so it would require a dedicated 20A circuit.
 
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