Protection for Three-Phase Energy Meter PCB

Question

I intend to measure 3-phase power grid supply using three energy meter boards that will be connected to an ESP32 device, the current is measured using Current Transformers (CT) that came with the energy meters. The board does not contain any protection measurement such as MOV, fuse etc. I have tested each energy meter individually and they work fine. The schematic is attached below of the energy meter.

Additional information: In my house, we have 3-phase grid supply which is monitored using a Voltage protection relay which trigger a contactor if supply is okay. Thereafter, we have a 4 wire RCCB/RCDB and thereafter single phase MCB for devices/equipment in the house. We don't have any SPD device.

Assumptions:

1. My intention is to place it after RCCB because my understanding is that it will trip if there is any short between any phase and neutral.
2. The voltage protection relay will protect the circuit from any overvoltage, undervoltage and phase loss so no need to worry about over voltage except any surges from the grid.
3. Only issue can be the short circuit between the phases or phase(s) to neutral.

Questions/Concerns:

1. How to protect the board from short circuit between line to line?
2. How to protect the board from short circuit between line to neutral?
3. Anything else I should be concerned for such circuit?

Answer 1

Measuring inputs typically are not protected because they are high impedance. They are supposed to measure often up to 25% over. They are not damaged by surges when well designed.

The wiring must be fused with suitable fast blow fuses to protect the wiring the case of short.
An RCCB may protect against failure of isolation barrier, it will not protect against short circuits.

A short circuit on the metering board will vaporize traces and cause a spark. There is nothing to prevent.
Too much energy is available on the primary side.

My recommendation is you find a 4-pole fuse holder and insert low value fast fuses, such as 100mAFF. An RCCB can be placed before or after.
Such that you can also safely isolate the meter when accessing the ESP32 by pulling the fuses.

I will assume that you have a touch safe enclosure for these boards when in operation.