Build a Power Splitter

What you will need:

Wiring diagram:

The inner core joins pins 3, which carries the audio and call lamp signalling. The screen of the cable is connected to pins 1, this is the ground. The pins 2 are left unconnected, and this isolates the two sets of power supplies. The bodies of the XLR connectors are not connected to anything, ie they are left floating.

Finally, ensure you label the cable so that it doesn't get misused! How to label the cable? I tend to put a written (well, computer printed really) label under a bit of clear heatshrink, so that the label never comes off.