I recently installed my IoTaWatt, and I’m having a few measurement discrepancies that I’m unsure of. I’m in Canada, in a home with 2x 100A 120V split-phase power service, ECS24200 CTs on the main lines and 4x ECS1050s on other circuits.
One of the circuits I’m attempting to monitor is a 2x 120V 30A breaker for a clothes dryer. I read a related thread on this (Question about monitoring clothes dryer) and it seemed like the simplest approach was to pass one conductor in the opposite direction through a single CT (ECS1050). I didn’t care about measuring the individual power on each leg, but thought this approach would get me the total power usage.
When the dryer is running, things look about right… there’s draw on the both Mains, and a reasonable looking power usage for the Dryer.
When the heating element isn’t active is when things start to look strange, as the Dryer circuit appears “reversed”. My interpretation of this is that the direction I clamped the red & black wires / orientation of the CT is inverse of what would be needed for the 120V leg running the dryer motor to be “positive”. I could either flip the CT, click the reverse button, or ignore the reverse arrow; but regardless my measurements seem plausible…
But then I also noticed that when the dryer motor-only is running and the rest of the house’s power draw is low (relative to above, the “Garage” circuit was shut off), the Main_B suddenly also shows a reversed draw. My 200A CTs on the mains are installed in opposite directions from each other, and generally don’t show this icon:
So I’m not sure what that means. My best guess is that the current on Main_B in this screenshot is so low that measurement errors are creeping in? Any other possibilities?
I also captured this weird situation earlier in the day – here (Main_A + Main_B) is less than the power of all the other circuits, even though there is definitely miscellaneous draw throughout the house as well. If I take (Main_A + Main_B) and subtract all other circuits, I get -55 W.
Both of these two situations feel like the same thing – small scale measurement error. Is that the right analysis, or is it possible that I have I messed up the installation in a way to cause these discrepancies?