Hi,
I want to use a small stm32 or esp32 development board to monitor a motor encoder on an industrial machine (3 phase 415v electric). Do I need to do any kind of isolation for safety?

The machine runs on 3 phase 415v. The machine has 240v outlets that we use for an SBC and computer screen (they are also used for vacuum cleaners). I want to add the MCU to monitor motor speeds, buffer the readings and send to the SBC. I would either be powering the MCU from the SBC itself (sharing the power supply of the SBC) or I might power the MCU from the motor encoder's supply, assuming it might be 5v. There would always be data & ground between the MCU and SBC though of course (probably UART or SPI).

Is it important to do any kind of ground or signal isolation between these devices?

 

For pure electrical safety, no (but I would always check with a meter for proper connections or mis-wires first and abide by any plant requirements) if the MCU and SBC has a normal power supply with galvanic isolation from the utility lines. Signal isolation of the encoder signals is usually a good idea for signal integrity and RFI/EMI reasons because of wiring near the motor.

What type of encoder and what signal type do you want to monitor?
https://www.digikey.com/en/articles...utput-signals-to-aid-optimum-device-selection