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I have a client who keeps roasting their PLC processor which sits in a small building in the middle of a field. The 480VAC 3 phase power to this building is fed underground from switchgear about 1/4 mi away. An MCC and transformers are inside the building to knock the power down to 120/208 which feeds a breaker panel, which then feeds the PLC. There is local digital I/O to the MCC buckets, and remote 4-20 mA signals fed underground to monitor flows, pressures, etc. An RS-422 link (also fed underground) allows the PLC to be networked to others and to the SCADA system. The roasting of PLC's seems to be directly related to inclement weather/thunderstorms, and I am pretty sure that we need some sort of lightning/surge protection. The PLC is the only 'electronic' item in this building, and it is the only thing to have ever failed. The question I have is where should this protection be? On the 480V 3 phase? On the breaker panel? In the control panel? Should I also protect the RS-422 comms? I know that there are various technologies for lightning protection...Any advice on which to use? Recommendations on vendors? Info/tutorials on-line? Thanks in advance! Jeffrey R. Gee