Not a lot to go on here, but certainly seems directly related to the AC unit. What sticks out to me in the above graph is:
The lapse at about 15:18 seems to begin when the AC comes on, and continues for a few minutes, then starts working again before the end of that AC cycle.
The lapse at about 15:24 also seems to begin when the AC would have come on, and ends about where the cycle ends.
There is another anomoly at about 15:53 where mains1 spikes briefly. That is inconsistent with the other normal cycles.
I’m assuming that the AC actually ran during the first two lapses, its just that the IoTaWatt wasn’t measuring anything. Even in the graph from yesterday, the voltage was not being measured properly.
By elimination, I conclude that what is going on is that the voltage signal is not symmetrical during those periods. One of the ways IoTaWatt checks the viability of a cycle sample set is to compare the number of samples taken between the zero crossings i.e. the “positive” and “negative” portions of the voltage cycle. If they differ significantly, the entire sample set is discarded. This is one of several integrity checks on the sampling and is intended to detect if an interrupt compromised the sampling. So the question is what could be triggering that?
I’m getting away from my comfort zone speculating about what is going on with this relatively complex AC system, but I’ll just throw a few things out there. Maybe they’re valid, maybe not:
Given that everything comes on at once, there is probably a tremendous inrush current. Looking at the Locked Rotor Amps of the compressor, it can be as high as 105 Amps. We are seeing about 42 amps at the time of the event, but that is an average potentially over a few samples, so it could be much higher for one cycle.
So it could be a starting issue, especially looking at that 15:53 event (and the tail end of the preceding cycle). Maybe something with a relay, or a capacitor in the starting circuit of one of the single-phase fan motors.
I’m also wondering about why the electrician mentioned a ground problem. Given that the compressor is delta wired (400V), the line of phase A (the VT) is connected to both of the other phases while that motor is running. If the ground is bad, I think the voltage could swing back and forth toward the other phases on a cycle by cycle basis and cause the asymmetry that would trigger this problem. This is not the macro level voltage that you see in the graph, I’m talking about the actual voltage during each individual cycle. It could even work out to a decent RMS voltage, but just not symmetrical enough to be acceptable to IoTaWatt. This could be a broader three-phase issue, although there has only been one other problem that might be linked. I can raise the threshold that triggers the sample rejection and see what happens.
The other issue that hasn’t been mentioned recently is the “flickering” that was previously reported. My suspicion is that these two are related.
So going forward, I’ll change that threshold in the next release and see what happens. Maybe even put in a temporary way to set it in the configuration so we can experiment.
You will have the electrician check things out, although I suspect the issue is in the AC unit rather than the general wiring as it’s intermittent.