If the DC system is grounded, then the AC and DC grounding electrodes must be tied together. If not there will potential differences between the 2 grounding systems that may lead to problems. About 15 years ago we installed a DCS control system where the manufacturer insisted on an independent grounding system for the DC ground. No connection to the AC ground was permitted, other than the earth. For the first three years every time there was a thunderstorm in the area, boards would be burnt out on the control system. We told the manufacturer that the grounding systems should be tied together to eliminate the problem. They insisted otherwise and had us repeatedly prove that the two grounding systems were independent. After the third year of burnt out boards, they let us tie the grounding systems together. The problem went away.
Don(resqcapt19)
