The 140XBE10000 Back-plane expander and Cable allows you to add a second back-plane to a local or remote drop.  The cable (P/N 140XCA71703/6/9, depending on length) can be 1, 2, or 3 meters long respectively.  The back-plane expander modules are identical, with the module located in the rack containing the CPU or RIO adapter considered Primary.  The cable ends appear to be identical; however, the cable end with the label closest to it is considered the Primary end.  This end MUST be connected to the Primary XBE module, and will not work when reversed. There is no indication if the cable is installed incorrectly.  Also, the cable must be installed before applying power to the back-planes.  For further information, please refer to the Quantum Automation Series Hardware Reference Guide (840 USE 100 00).