I have an emonTx monitoring the in-coming 3 phase supply at one of the premises I use and am a little puzzled by the readings on one of the 3 phases (L1 Red) which presently has very little load.
The supply to the voltage reference is on the incoming L3 (Blue) phase (because that is what happens to be available on the socket by the incoming supply cables) and that is the one connected to CT1 (P1) input, with CT2 (P2) on L2 (Yellow) and CT3 (P3) on L1 (Red).
However today a heater was added for a few hours and this saw the measured figures on L1 (Red) go negative, so where I had originally placed the CT sensor one way around I came to the conclusion it must have been the wrong way so I have turned it around.
However that means now when the heater goes off the power used on that phase shows around negative 300W - I have checked the current calibration figures in the emonTx_3Phase_PLL_V1.7 firmware and they appear to be correctly showing 90.9 and I have swapped the CT sensor for unused one that I have and the result is the same.
I swapped the CT2 and CT3 sensors around, but that just showed the -300W appear on the other chart.
Is there anything else I should check or can do to try to improve the readings ?
I have another emonTx that I could try, but have not yet done that.
In case in matters I’m using a USB-> serial connection from an emonPi to the emonTx and the Radio is disabled.