Question

[hvanoch]

I also have an SDM630 hooked to a 3fase net without N. I also see that I don't get a reading for the L2 power consumption (Watt) (always 0). I only get values forL1 and L3. Do you know why that is?

[niobos]

Hi @hvanoch,

You have the same kind of power supply than I have. In the readme.rst, I included a sample output that I get. And as you noticed, you get only two power measurements. That is because there is nothing more to measure:

For a 2-wire connection, you can measure 1 voltage (between the two wires). You could measure two currents (one per wire), but they'll be identical (but opposite, obviously). Therefore, you only have 1 power measurement to calculate.

For 3-wire connection, you pick a reference wire (just like the 2-wire case, L2 in case of the Eastron) and you can measure 2 voltages (U1=L1-L2 and U3=L3-L2), and 2 currents (I1, I3). The 3rd current (through your reference wire, I2) is the sum of the two measured currents. You can calculate two power measurements (P1 based on U1, I1; and P3 based on U3, I3). Loads will either show up in P1 (when connected to L1-L2), in P3 (for L2-L3), or half in both (for L3-L1).

Notice that I discovered that my Eastron Firmware calculated I2 wrong, so this code re-calculates it and ignores the reported I2.

For 4-wire, things are easier, since loads are usually put between a Line and the reference (neutral), and you have no loads that split over multiple measurements.