Microwave Dedicated Circuits

KennMacMoragh

People keep telling me that microwaves need their own dedicated circuit. Does that apply to microwaves that sit on your counter top and plug into the wall? Or does that only apply to microwaves that mount to the wall above your range? So if someone has a counter top microwave already and they want a kind that mounts to the wall, do I have to tell them they need a new dedicated circuit installed for it?

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angus242

I don't have the answer but over the range microwaves have external lights and a fan in them so they probably draw more amperage than a counter top model.

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thom

If it's a built in, it needs it's own circuit. If it is portable and sits on the countertop it does not need it's own circuit. If it's one of the microwave/hood combinations it needs its own circuit.

Then check local laws. My community requires all microwave/exhaust hoods to be energy star rated. The federal governments web-site for energy star says microwave ovens are not rated. So, my community requires something that does not exist. I will be dealing with the city in the next week on this issue.

480sparky

Funny. I don't see the word "microwave" listed anywhere in Art. 210.

210.11(C) contains all the required residential circuits.

Methinks the answer is in 210.23(A):

(1) Cord-and-Plug-Connected Equipment Not Fastened
in Place. The rating of any one cord-and-plug-connected
utilization equipment not fastened in place shall not exceed
80 percent of the branch-circuit ampere rating.

(2) Utilization Equipment Fastened in Place. The total
rating of utilization equipment fastened in place, other than
luminaires, shall not exceed 50 percent of the branch circuit
ampere rating where lighting units, cord-and-plug connected
utilization equipment not fastened in place, or
both, are also supplied.

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KennMacMoragh

That's what I don't get, whether it's built in or sits on a counter, what does that have to do with the electricity? Even if it has a fan, if you were to run the microwave and a toaster at the same time, the breaker would trip if on the same circuit.

I talked to a gal thinking about taking her microwave and just sticking it inside one of her cabinets. There's nothing to stop her from doing that, it would plug into the wall the same way a counter top microwave does. But if I installed cabinet sides around the microwave, then it would be considered "built in", so now all the sudden it needs a new circuit? So to find a loophole, you could put it up on a shelf, or inside a cabinet, as long as it wasn't mounted in and you could take it out?

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thom

Well Ken and 480, I'm just telling you how our inspectors enforce the rules. Arguing a point with them seems to be counterproductive. Sure, you could sue the building department but the time and cost associated seems a bit out of proportion to the cost of adding a circuit.

Here we put in two countertop circuits with 4 receptacles each max. They will allow us to stretch that to 5 receptacles if one of them is for the controls on a gas range.

Disposal and Dishwasher may be combined on a single circuit, but nothing else on the circuit. Built in microwaves on their own circuit. They will go so far as to tell us that if it's an open cabinet with a microwave shelf, it must have a dedicated receptacle.

I don't make the rules, I don't even interpret them, I just do it the way the inspector insists.

For a while one of our inspectors insisted that our laundry circuit, for a clothes washer and gas dryer had to be two separate circuits. Fortunately after a couple years he gave up on that one.

480sparky

No one can take advantage of you without your permission.

You have given them permission.

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Tinstaafl

Disregarding the NEC and/or local codes for the moment, it's just good sense to have a dedicated circuit for any permanent or semi-permanent high current device.

Some of the people telling you that may just have been trained to do it that way without having the reasoning explained to them. Or it may be a local regulation.

It's not required here, but I always do it in new construction, and recommend it (with explanation) when remodeling. As long as the cost of adding such a circuit isn't exorbitant, the HO almost invariably agrees to have it done.

GettingBy

If it pulls 12A there's not much left for other appliances.

DuMass

If it’s an OTR microwave/hood it would be considered a range hood. If it is cord and plug connected it would be required to have an individual branch circuit, regardless of the nameplate rating. See 422.16[B],[4],5 in the 2008 and 2011 NEC. Now I’ll bow out of the conversation before someone accuses me of trying to one up them.

480sparky

Once again, with a correct reference?

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DuMass

Done!

cleveman

funny, my inspector let me run the OTR microwave/exhaust on the same circuit as the gas range. As he said, " the stove lights and clock, etc. won't pull much". comes back to 480's code quote, otherwise the micro and stove couldn't share the same circuit.

GettingBy

And so they don't.
If adding a new circuit to a finished house was cheap I guess everyone would wait for nuisance tripping before adding one.

On average, houses only draw a kilowatt, 8A @ 120V. The problem is they occasionally draw much more than this.

Tinstaafl

Not necessarily disputing, but wondering where you got this number?

GettingBy

Of course I lost the link but there's a site that has houses pulling 8700 kwh/yr, very nearly 1 kw continuously, with some houses in the NE pulling 4x this value. Some houses in the US must not use AC in the summer.
I believe Al Gore's house pulled 20 kW until this tidbit was published in Washington Post. I guess he liked to arc weld. . .? Hypocrisy, thou art named Al.

With each house having energy storage in flywheels the service to houses could be 4 A to 16 A @ 240 v and the flywheels would handle peak demand. It'd put the copper industry out of business.

480sparky

First.... it's an average, not what it constantly draws at all times.

Second... I have many first-hand accounts of reading residential amp draws. Less than 10 amps when there's no AC, water heater, dryer or range running is very very common.

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Tinstaafl

Yep, knew that.

I haven't measured the draw on too many homes, but with several power outages a year here lasting more than a couple of hours, I've become pretty familiar with what I need for a generator. 5KW is extravagant; 1.5KW is comfortable with some common sense.

'Course, we have a gas range and don't run the electric clothes dryer at such times.

480sparky

Here's a 75-minute recording of an actual service draw:

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GettingBy

Your electric meter will tell you the average draw over an hour, a day, a week. . .

It can also be used as an ammeter if you have a calculator and a wristwatch.

By eyeball, the avg. draw of Sparky's waveform is way less than 1.5A if the Y axis is in amps. At 240V it's less than 360W.