MSB or FA-DUINO has small relay inside.
Sometimes the included relay is not enough to turn on and off a large load. At this time, you need to additionally use a large extra relay.
To remove spark when extra relay turn on/off, we recommend use Surge suppressor.
Look this power measurement result without Surge suppressor
Can see this spark signal on power line when external Relay turn on and off.
If add Surge suppressor like this:
Surge will gone.
if you don't use Surge suppressor looks like working fine. but huge demage goes to main circuit, finally make a problem.
I saw many user's control panel don't use Surge suppressor, they said “my machine often stop or reboot. I don't know why!”.
Surge suppressor price is very cheap, and very useful at your circuit.
refer this other company user's manual.
This is EATON's PLC manual. They said same story.