If you are running a 50mm DB2 underground conduit, for a 2-wire, single phase 600V system (no neutral) between two lighting panels (which have a 600V to 120V transformer) is it mandatory to run a third wire as bonding conductor(to ground)?

The panel themselves have their own grounding electrodes.
The 600V circuits are #2Cu, so in general the code would call for a #6 bonding conductor.

What is the CEC rule/subrule that would make the bonding conductor mandatory? I am not sure I read 10-106 properly.