OK, I found it: Origin2000 and Onyx2 Deskside and Rackmount Installation Instructions Document Number 108-0155-002 12/96 pg. 6-36 "Caution: You cannot install CrayLink interconnect cabling on a standalone deskside system because of power grounding requirements. The power differential between two interconnected modules should not exceed 500 millivolts; otherwise severe damage can result to boards and other components inside the chassis. The power distribution unit (PDU) inside the rack provides a common ground source for the modules. In addition, the groundstraps are installed on multirack configurations to help provide common grounding across the racks as described in Section 6.16" That seems about as blunt as you can get. -- "The Direct3D Graphics Pipeline" -- DirectX 9 draft available for download <http://www.xmission.com/~legalize/book/download/index.html> Legalize Adulthood! <http://blogs.xmission.com/legalize/>