Adding a microwave to circuit


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Old 08-31-05, 08:18 AM
B
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Adding a microwave to circuit

I want to add an over-the-range microwave. I had a range hood there with a light/fan, however, it is on the same circuit as my living room overhead lights and multiple plugs, therefore when I turn the microwave on all the lights dim a bit in the living room, but no breaker goes. It isn't a terrible problem but am not sure of what is going on electrically.

I have an outlet near the range that is on a different circuit, the breaker only controls about 6 receptacles, two in the kitchen and 4 in the dining room, and no lights. so my idea was to tie into that circuit and run a line up to the microwave (up in the cabinet that is just above and over from the receptacle, don't even have to go thru a 2x4).

so, the receptacle that i'm trying to tie into has the following connections in the box--2 lines coming in, both black wires go to the receptacle on one side, both whites going to the other side, then the grounds connected and on the green screw.

so if i'm correct, the outlet is midway thru the circuit. i was hoping i could do the following. run a line from the receptacle i'm talking about up to the microwave, then my connections at the receptacle box to bring power to the microwave could be: cap all three whites together (the two there and one additional from my new line), cap all three blacks together, run a white and black conduit from the sets of three capped wires to the outlet that is there. Then I'm done.

Any thoughts/problems with the above. also, one of the 6 outlets that the microwave would be on the new circuit if i made the above changes, is the outlet that i use with my computer. i have a surge protector, but is there any problems with this.

bryan
 
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Old 08-31-05, 08:28 AM
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In 99.5% of the cases, the installation of an over-the-range microwave requires the installation of a new electrical circuit. Trying to use any of the existing circuits is almost always a really bad idea (and most such solutions, including the one you propose, violate a bunch of electrical codes anyway).
 
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Old 08-31-05, 09:57 AM
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I understand that ideally a new circuit would be created. However, a circuit was already in place since it has a range hood with a light and fan. What codes are being violated? I know multiple folks have an overtherange microwave that isn't on its own circuit. Obviously the expense is a large concern, and if I can run it without blowing a fuse, then it should be safe. I was going to install a GFCI on the new circuit as well. The old microwave was plugged into the circuit that I want to change to run the new microwave.
 
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Old 08-31-05, 10:11 AM
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Like John, I am certain that the installation manual for your microwave calls for a dedicated 15 or 20 amp grounded circuit. Most of them do so in bold lettering, because it is very important. GFCI protection is usually not required on this dedicated circuit.

The existing range hood probably draw at most 2 or 3 amps. An over-range microwave draws well over 10A; some units draw up to 15A. The existing circuit in your kitchen was designed to accomodate the much lower load of the old range hood.

Regarding electrical code, the kitchen is the most heavily regulated room in the house; and rightly so. People use lots of water, electricity and heat all at once and safety from fire and electrocution is critical. The specific codes John refered to are: kitchen countertop receptacles can serve no other loads than kitchen countertop receptacles; built-in appliances (like your microwave) must have a dedicated circuit if they use more than 50% of a circuit's capacity; and finally, built-in appliances must be installed and wired as per the manufacturer's instructions because only that configuration has been tested for adequate safety.

The only correct way to install this microwave is to run a dedicated circuit from the panel box to the microwave, just like it says in the installation manual. Sorry if that's not the news you wanted.
 
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Old 08-31-05, 10:11 AM
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A range hood with light and fan uses about one-tenth to one-twentieth the amount of power as a microwave. So you can see that you're not just swapping one thing for another.

Code prohibits lighting and and fixed appliances on a circuit serving receptacles which serve the kitchen countertop. The idea is to leave sufficient power available for all those countertop receptacles so that you are less tempted to do something stupid. The rules are different for microwaves that sit on the countertop.

There are other codes which restrict the percentage of a circuit that can be used by a fixed-in-place appliance to 50% when that circuit serves other loads.

You may not like these codes, and you may not even care if you violate them or not, but I do think you should be fully aware of what you're doing and be willing to accept the risks. Code violations, even if they don't bother you now, often come back to haunt you when you sell the house.

So now you are informed. Do what you will.
 
 

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