these are picopsu 150w, connected to dps-2000bb 2000w psu 4kw(2 x 2000w psu together) unit connected to a ap7811 PDU. after spending most of the day looking and testing components i think it was from no ground points to the motherboards. since picopsu's don't have grounds in the atx connector like a normal psu. I was thinking the 2000w psu's would be grounded and them touching the tier shelving would ground mind you the bottom tier isnt touching the 4kw. I have an old system sitting around and will use it to test the tier shelving out, this time ill put the system on a piece of wood or cardboard to separate it but ill also ground the board at the screw to the PDU unit (common ground). unless im missing anything, as for metal etc ive had no issues in the past with it but i have always used a normal PSU and not a picopsu.

the 4kw can easily handle 4 systems of 6 cards, especially when its not mining. im running 6 systems with 2 x 4kw psu units 4-2. the burning occurred right when i power the system on.