Q. How do RAC and Waitlists all work???
Ans. When all the available seats/berths in an individual train/class have been sold, the railways start selling RAC tickets (2A, 3A, FC & SL only), when all the RAC tickets have been sold, then a waitlist is started for all the train classes, and you’re sold a waitlisted ticket.
As people cancel tickets, a RAC/WL ticket will move closer to a confirmed berth. Also, when the final reservation chart is prepared, any un-sold quota berths will be used to reduce the RAC/waitlist.
Tickets...
more... will be sold in the following order....(4 RAC places in this example)
Available 02
Available 01
RAC 01
RAC 02
RAC 03
RAC 04
WL 01
WL 02
and so on...
Source: bit.ly/IqRG4