VM3P75CT power measurement difference to grid meter ~10-20W

[MSl1]

Hello!

The VM3P75CT (VM3) is calibrated according to the manual, the device itself and also every CT separately.

However, I ALWAYS see a difference of approx. 10-20 W in the measured power in my Home Assistant Logs compared to the grid meter (Germany: mME Landis Gyr E220 ).
The CTs are connected correctly, L1-L3, and on the first available phase cable after the grid meter. The VM3 with his load is definitely connected behind the grid meter.

If I set the grid point to ZERO in the ESS settings, the grid meter show values about + (10…20)W in the middle. (Currently in the screenshot ESS, Grid Point=20)

Who is going wrong?

A “True, Reactive, and Apparent Power” problem?

The VM3 shows in Victron Connect, Total Energy forward=94.5, reverse=5.8. The grid meter difference since the last VM3 energy reset (31.10.25) is: 104.5 kWh. (1.8.0 is energy IN)

[mac]

This might be due to the low current, see this thread for example.

Is there a problem with the installation?

[MSl1]

Thanks!

There are NO problems with my ESS installation.

My workaround is to set the ESS grid value to -10 or -20 to reach the grid meter power value nearby ZERO.

[MSl1]

Some reading material:

Benutzerhandbuch-E220.pdf

https://www.energieverbraucher.de/de/eich-und-fehlergrenzen__746/

Assuming a grid meter class A with 10%. My energy values of november:

VM3: 94 kWh

E220: 104 kWh - 10% => ~90 kWh

Conclusion: If I would install another VM3 (with other CTs) or another grid meter, i would see other energy values in both systems.

… btw: 10% Verkehrsfehlergrenze (Traffic error limit) means in case if yearly grid costs of 2000 Eur → 200 euros paid too much or too little.

…I have found the real error class of my grid meter, class A / 10%: