Motor Startup wattage


New user here and have been running the energy monitor for a little over a week. First device detected was my well pump and no surprise there. I was told that Sense would detect the startup wattage of of the motor but I don’t think it is. I have a deep well with a 1hp motor and it shows up just fine but its always running at just over 2000 watts. I expect this but was thinking I would see closer to 3500-4000 at start up. I need this data to help size my generator otherwise I would not really care. Thanks for any advice!


At that many watts, your pump would be 240 volt. It is very common for Sense to only
detected one leg of service but will probably detect the other side eventually.
If you look at the total wattage instead of the tag on your timeline then I would
wager the total reflects the correct wattage while the tag is half.
Give it time, it will catch the other side eventually.


A couple more questions:

  • Where are you reading / viewing the 2000W ? Post a screenshot if you can.
  • How long do you 3500-4000W startup to take - just a few millisecond spike, or several minutes ?

Sense does the same thing to my 1.5 HP pool pump. It only detects 1 leg of the pump.

Here (first image) is the actual startup of the pump, the startup spike is 3282 watts.

Here (second image) is what Sense shows for the pump it’s identified, the startup spike is 833 watts. The other leg is being reported in Other.


Thanks for the replies to my question. Yes its a 240volt pump and yes the startup surge is a fraction of a second. My generator transfer switch has 2 analog watt meters on it and when the pump kicks on they both (very quickly) peg all the way to the right side and then drop back to the total of about 2000 watts. The thing that’s odd in sense is that I can’t see this anywhere even in my total home watts. For a 1hp pump the 2000 running watts is correct but it should show startup wattage of like 4000. Maybe I just need to wait for Sense to fully detect both legs?


If you are seeing 2000W steady state from Sense, and that’s what you expect, then Sense might have already detected both legs. And if you are expecting a sub-second spike, remember that even though Sense is taking microsecond readings, it’s aggregating one-half second RMS power results for your Power Meter viewing pleasure. Spikes can get partially averaged away.

We could be more helpful if you posted the Power Meter view of the startup of your well pump.


True, Power Meter usually doesn’t show the spike. Today, I have the startup spike on my pool pump. Still only showing 1 leg.


I think its just not showing the spike when the pump first kicks on since its a split second spike. Here is the power meter showing the pump. For some reason I can’t find this same screen on the website only on the app.


Yup, it looks like the spike is getting truncated due to 1/2 second averaging. To get a similar display in the web app, you need to select the Meter. Slightly different, but better laid out for a computer screen.


Certain devices don’t show the spike. I believe most of the devices that have a spike on inrush last for at least a half second but maybe not.

I was told after I suggested it that some spikes are filtered out simply because they’re so far from the rest of the data that it would cause viewing issues for the general user.

Example, my heat pump shows a fixed (false but at least detected) 6500 watts total. On startup, it’s 13000ish watts PER LEG. I believe its a scaling issue or on purpose. A refrigerator or smaller device’s start is usually small enough to ‘fit in’.


That makes sense (no pun intended). It would be nice in the device section to be able to see a max wattage number. Likewise, is there no place to see total wattage besides looking at the chart? I would like to know the most wattage my house has ever used as well. These things are crutual in using the device to size a generator for the home. Running wattage is great but does not tell the whole story. Thanks everyone for feedback on my question. :slight_smile:

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BYW - In the web app, you can look at the Meter at a Month’s usage, possibly zoom out a little more, and get a good idea of you max 1/2 second RMS usage. Probably have to guardband by 1.5x if you want to calculate for a spike level that might stymie your generator. Or if AC is your most trying electrical usage, you might have to wait for the right season first… My last month, plus a little extra from zooming out.


Just for the sake of reference, and perhaps to throw a complete wrench in the discussion, some motors can be equipped with soft starters which are designed to soften the startup load. There’s also variable speed motors that do not generate the expected startup surge at all - the newer crop of “linear compressor” refrigerators are a great example. Here’s my new LG Linear fridges startup signature for example:

It’s possible even a hefty single speed electric motor (IE, a furnace fan) with a digital soft start unit that is set to a very gentle curve could completely eliminate the surge that we all expect to see on Sense with inductive loads.

The most common application of a VS motor that one would expect to see at the consumer level would be a variable speed pool pump. Anyone who owns one knows that they start up extremely slowly and only ramp up to the speed configured. There would be virtually no surge startup signature whatsoever for a VS motor despite the fact that they can be quite significant large HP motors.


And some motors are DC motors or electronically controlled AC motors. Garage door openers with battery backup are typically DC. Many variable speed AC motors are electronically modulated. Neither of those types will have a spike or a corresponding phase angle (inductive) signature to them.


Yes, maximum wattage on a branch is important for solar inverter sizing.
You must know the maximum so you don’t trip the inverter.