Microwave using quite a bit more power than rating plate indicates

Hey all. I’m a new sense user and have spent way too much time the past three days staring at my energy meter – super cool.

Anyway, I noticed a consistent 2000 Watt draw when I use my microwave which seems quite high. It’s on a dedicated “microwave” 20A breaker but that’s slightly more than the max 80% of 20 Amps which I thought was the guideline.

The microwave is a Panasonic NN-SN651B and it lists an input of 12.4 Amps so it appears to be drawing 34% more than expected. The microwave works fine but this seems… a bit disturbing. The sense seems to be accurate for other loads I can measure through different means so I tend to trust the measurement. Anyone else experience extra powerful microwave ovens?

Microwaves definitely use more energy than their specced output power, but should come close to matching their specced input power.

Maybe you can post a screenshot of your Power Meter showing the microwave in action ?

I have the same microwave, draws 1800 + watts. Confirmed with two other means of energy monitors. Have looked into it before, seems it’s the case with all of that model.

My microwave is part of a double oven and on a 50 amp circuit. It pulls about 1800 all the time

Here’s the model if curious

Here are some pictures of a one minute run on the default power level. It’s not identified by Sense yet but it’s very consistent and this is with my power lines very quiet.


entire minute


before


during

It seems to be using quite a bit more power than expected.

If you want to verify that it’s correct, grab a kill-a-watt meter from Amazon, Home Depot, Walmart etc for $25 and see what you get.

I would agree that over 2k is unusually high for microwaves based on my non scientific, googling. How old is the unit?

Edit:. The kill-a-watt isn’t rated for power consumption at the levels provided by the OP. While they are great tools, using one in this case would not be advised.

I have a kill-a-watt (they’re great) but I think its limit is 1500W. Looks like the microwave is about 6 years old.

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I would pick a “Traveling” Kasa KP115 over a Kil-A-Watt, because the KP115 can pull longer term data straight into Sense, so you can see the full time history of the device’s power usage over time.

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I suggested the kill a watt over the plug in this case because the plug isn’t rated for continuous use at that power level. The OP would be exceeding the max rating by quite a bit with a KP115 on the microwave.

Edit: I see the kill a watt would be exceeded as well.
The one I have will do up to about 1900w. Don’t do either then :man_shrugging:

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You’re right. The KP115 is specced at 15A, 120V, 1.8kW. But the good news is that the internal relay is specced at 16A @ 250V. Still not enough really, but I might try as a temporary thing, just to capture the typical microwave waveforms.

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I’m sure I would try it as well, monitoring the device while I do, I just wasn’t going to advise that :joy:. Makes me wonder though if it would even report above the 1.8.

It seems very un logical & unsafe to pull more power than the standard 80% of a nema 15 plug.
12 amps (80% of 15 amps) @ 120 volt =1440 watts
As you stated it is rated at:
Max Power Consumption 1480 Watt
source:

&

If this microwave would be really pulling 2000 watt, that would be in direct violation of all NEC codes/requirements/approvals.
I can not believe it is really pulling 2000 watts.
Since you mentioned you noticed it pulling 2000 watts, how/where did you see that?
Can you post screenshots? ALREADY DONE

UPDATE
I was notified screenshots were posted. I just didn’t notice them. Sorry about that.
2641-634=2007 watts

The NEC code requires 80% rule for something that will draw power over hours of time.
A microwave doesn’t do that, full power for hours.
So the max the microwave would be allowed to go is 15 amps x 120 volt = 1800 watts.

I can still not imagine that a respected manufacturer like Panasonic would state “max 1480 watt” but IRL would go 2000 watts meaning they exceed the max power of nema15 outlet by 2007/1800= 11.5%
That would be such a liability.

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Thanks for the screenshots - seems to clearly show 2000W consumption. Two thoughts:

  • How well has your Sense been correlating with your overall house usage and electric meter ? Just wondering if you might have a calibration issue on you mains.
  • The slow ramp of the microwave is identified as two transitions by Sense (the two tags). That slow ramp might impede detection.

Seems to correlate well. I have my dehumidifier on a kill-a-watt showing about 280W which is right around where the Sense has it. The lightbulb measurements seem to be accurate too. The bigger stuff I haven’t double checked but anything that plugs in and is under 1500W I could check with the kill-a-watt.

This is only my 4th day with Sense. I’ll see how well it tracks my meter.

Thanks. It’s on a dedicated 20 Amp circuit though but still a little over 80% of that. Maybe the 80% rule doesn’t apply for the use case as you said. I agree it still seems odd it would use more power than they claim.

If it is fitted with a normal nema 1-15 amp plug it is rated for 15 amps.
nema_1-15p

Would be allowed a peak while the device starts up, maybe even to 20 amps for a few seconds but the moment a micro wave is not allowed to pull 16.725 amps through a 15 amp rated plug.
For that they invented the nema 1-20 plug
nema_1-20p

So I still have a hard time believing that they would pull 2007watt through a “normal” plug.

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Yeah, it’s a NEMA 5-15 plug so I guess that’s more evidence that there’s something wrong. I’m going to stop using it. Thanks.

Do you have access to either kill-a-watt or one of those smart plugs that can measure energy?

If so: plug it in between and get a second reading apart from Sense.
Since it has inverter technology, there isn’t a giant peak when it switches on (like an ‘old school’ microwave does)
I would run it for 10-20 seconds and take a reading with something in series (energy reader).
If that confirms >2000 watt, I would call Panasonic and start asking questions.
“what happens if my outlet catches fire because the NN-SN651 pulls more than the allowed 15 amps from outlet ?” would be my favorite question to ask.

But please perform a confirmation reading first.

Whirlpool WMH32519HZ 30 Inch Over the Range Microwave Oven with 1.9 cu. ft. Capacity, 1000 Cooking Watts, Ducted Venting, 300 CFM, 10 Power Levels, Add 30 Seconds, Turntable On/Off, Popcorn Button, Sensor Cooking in Stainless Steel

2 Minutes exactly

Full Power - 10

“1,000 cooking watts” in listing above -1523 Watts according to Sense/KASA

So 52.3% above description


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Cooking watts is the amount of power that heats whatever is inside the microwave.
You have to add to the overhead of everything in the microwave, including the motor that turns the table etc.
From the feature sheet:


16 amp rated.
15 amp x 120 volt = 1800 watt ← max power from nema1-15 outlet
16 amp x 120 volt = 1920 watt ← specification
So your microwave is imo not asking more than specified and allowed according to NEC rules.

From the installation manual:

Dedicated 15 ( or 20) amp circuit for just this unit.
But even with the 15 amp outlet, it doesn’t even come close to what you are allowed to pull.

@lagomorph situation is different.
He either has a unit that surpasses the specs and the allowed power from outlet or the sense measurement is somehow not accurate.
Imo it would be good to somehow confirm the actual usage with a non-sense measuring device.

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