The P2 Interface is the connection between the fire control panel and the PAD-5 Main board. An isolator feature used to disconnect the outgoing FDnet from the main board if a short circuit is detected on the part of the FDnet. Due to the configuration of the PAD-5 with option expansion module, there is no polarity insensitivity, even if the expansion module is connected. Only the DPU programming port for programming the address is polarity insensitive.