Always arrange wiring such that the data source is at one end of the cable. DMX cannot be split by simply soldering 3 cables together. Dasy-chain everything, but see the section on isolation. 3.2 Line termination. All DMX lines must be correctly terminated if reliable operation is to be obtained.
Some equipment has a switchable line terminating resistor built in.
In these cases make sure that only the last item in the chain has its terminating switch set to on. You may like to back fill the XLR with potting compound or epoxy resin to provide protection. A simple DMX tester. This tester can be used instead of a line terminator to provide a simple means of checking for cable continuity. Build this into the back of a 5 pin XLR with the LED showing out of the back.