Solar 3-Phase System: Why Don't Solar + Grid Currents Equal Load Currents?

Dear all,

We just commissioned a Solar System 3phase with a maximum total output around 20A per phase in a 3phase 380V/50Hz grid.

When we check the current in each of the circuits we come with the following results:

Solar Circuit:
R:20A/S:20A/T:20A/N:0A

Public Grid:
R:30A/S:30A/T:40A/N:15A

Load:
R:40A/S:40A/T:50A/N:15A

As you see the total of Solar+Grid is not equal to Load.

If we then switch off the Solar Circuit we get the following readings:

Solar Circuit:
R:0A/S:0A/T:0A/N:0A

Public Grid:
R:40A/S:40A/T:50A/N:15A

Load:
R:40A/S:40A/T:50A/N:15A

Load=Grid

I also would like to add that the grid is connected to the bottom side of 1 main MCCB and the solar together with the Load cables are connected to the upper side of the MCCB.

I would like to add that the cables going to the Load are extremely hot and furthermore when Solar current decreat to 5A per phase seems that solar+grid= load

Can someone let me know what can be the reasons? Undersized cables? Unbalancing?

We never face that problem before and I don't know how to solve it.

Thanks

It sounds like something the solar system company needs to troubleshoot with their system, but here's my two cents worth.

The solar system may be driving current onto the public grid that is out of phase with the voltage. That might explain the seemingly "extra" current. You might confirm that with a Watt-meter.

If only the load cables are getting too hot and the circuit breaker is not tripping, I would say they are probably undersized. If the solar system or grid wires are just transferring heat to the load cables, those may be too small or it may be due to some other abnormal condition in the solar system that is creating heat. If you remove the solar system and the wires return to normal, then you can confirm the heat is coming from the solar system. If they stay hot, maybe they should be larger.