You’ve just validated one of the better Sense marketing claims, namely that many of us have unknown power consumption that adds up over time. Your discovery, with Sense’s assistance, just saved you about $50/yr, a significant part of your Sense investment.
It’s too bad that so much personal effort has to go into such discoveries, but you wouldn’t even have known to look without Sense’s nagging.
Very interesting. The cycling was the thermal protection in the motor cutting in and out as the windings overheated due to the locked rotor. Good catch as that could be a fire hazard as well as likely burning up the motor over time.
Good reason, @michael.d.sullivan, to not delete the device and let Sense take a look at the history. That data could be handy for identifying future similar occurrences. @JustinAtSense & @RyanAtSense will be interested.
great find, @michael.d.sullivan. Definitely share your story on Sense Saves, this is exactly the type of content we love to see posted there.
Nice detective work @michael.d.sullivan,
Can we add your single legged whole house fan to the community device library here ?
We like adding devices that have been discovered after a long painful search, in order to make it easier for future sleuths… It would be helpful to have a few more specs (Make/Model) on the fan.
Absolutely.
Thanks the new entry is here:
I took a couple liberties with your explanation, to move it from 1st person to third and to remove the word leg which has 240V connotations (and confused me for bit). I also subbed in @pswired diagnosis since that seems closer to the behavior (typical operation of the fan at max speed would be 4.9A x 115V = 564W - running at 848W is liable to trip the thermal protection)
LMK if you want changes…
Thanks as always @kevin1.
I’m really intrigued by this one and especially what @pswired points out. So given we now have the Sense recording of the potential (?) actual wattage during the locked rotor state, I assume you can extrapolate the likelihood of it causing a fire because that 848-564=284W has to go somewhere. Luckily the thermal protection was switching it off.
It gives hints to using Sense + a whole-house fan or other exhaust vents for a poor-man’s blowerdoor test of sorts. Smart plug overheating issues aside, I would definitely put a 120V attic/whole-house fan on a smart plug and a 240V fan on it’s own dedicated Sense.
Also, it’s worth noting that during normal operation, 90-95% of the motor power consumption is going out the shaft, not into the windings. With a locked rotor, all that power is going into heating up the windings. They’re not capable of dissipating that much heat without overheating.
I am confused as to why the motor was getting any electricity.
Electricity needs a complete path to move forward.
For example, if you are standing on a thick rubber pad (completely isolated) and touch a live wire with only one hand, the electricity does not affect. There is no path to ground.
How does the electricity go up one side of the wire, through the motor, then hit an open switch and still heat up the motor?
Asking for a moron friend. 
If a 120v motor draw current while a switch is open, if there is only one switch it must be because the motor winding or neutral wire is ground…if the switch opens the neutral wire.
If the switch open the line wire, the switch is defective.
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