I believe that BOB needs 24v to run the relay. See link for a wiring diagram. I've seen that BOB referred to a "China BOB" on forums.
https://wiki.printnc.info/en/electronics/wire-sizing
https://wiki.printnc.info/en/controllers/linuxcnc/bob
Link to manual
http://www.ijohnsen.com/blog/wp-cont...t_board-EN.pdf