The B8512G and B9512G have slots for two B430 Plug-in Telephone Communicators to provide redundant telephone connections.
Upon power up the panel uses the B430 in the Mod-1 slot until a Test Report is initiated or when the panel phone supervision declares the line currently in use as failed.
B430, B8512G, B9512G
Bosch Security Knowledge Base How long will the C472 stay keyed up before they stop transmitting and how long does the transmitter have to wait before it can send signals again? C472, Multilink, Fastlink