Hey Bloggsy.......we go further, the TCAS switch is never touched out of the TA/RA position unless directed by a non normal checklist or possibly if you desire during a PRM app in SYD to TA.
The Transponder is switched to Auto before start and back off after shutdown. Turning off the Txpd shuts down the TCAS at the same time.
Besides, in the AUTO mode the TCAS is inhibited on the ground anyway.