A system comprising: a first communications bus isolator; and a subordinate controller (570; wherein a first side of the first communications bus isolator is coupled to a first portion of external communications bus cabling, wherein the first portion of the external communications bus cabling is coupled to a first plurality of peripheral devices (510, 520, 550), wherein a second side of the first communications bus isolator is coupled, via external bus cabling receivers on the second side of the first communication bus isolator, to a second portion of the external communications bus cabling, wherein the second portion of the external communications bus cabling is coupled to a second plurality of peripheral devices, wherein the subordinate controller is coupled to the first communications bus isolator via a dedicated fault bus isolation output of the subordinate controller using a communications line that is different than the first portion of the external communications bus cabling and the second portion of the external communications bus cabling, wherein the subordinate controller is adapted to detect a fault on the second portion of the external communications bus cabling or on at least one of the second plurality of peripheral devices and transmit, via the dedicated fault bus isolation output of the subordinate controller and the communications line, a first signal indicative of the fault to the first communications bus isolator, wherein the first communications bus isolator is adapted to isolate the first portion of the external communications bus cabling from the second portion of the external communications bus cabling by actively disabling the external bus cabling receivers on the second side of the first communications bus isolator when the first communications bus isolator receives the first signal from the subordinate controller, wherein the first portion of the external communications bus cabling and the second portion of the external communications bus cabling are located outside of a control panel enclosure, wherein the first communications bus isolator includes a communications bus repeater, and wherein the communications bus repeater is adapted to automatically pass second signals between the first portion of the external communications bus cabling and the second portion of the external communications bus cabling when detection of the fault on the second portion of the external communications bus cabling or the at least one of the second plurality of peripheral devices is absent. a first communications bus isolator; and a subordinate controller (570; wherein a first side of the first communications bus isolator is coupled to a first portion of external communications bus cabling, wherein the first portion of the external communications bus cabling is coupled to a first plurality of peripheral devices (510, 520, 550), wherein a second side of the first communications bus isolator is coupled, via external bus cabling receivers on the second side of the first communication bus isolator, to a second portion of the external communications bus cabling, wherein the second portion of the external communications bus cabling is coupled to a second plurality of peripheral devices, wherein the subordinate controller is coupled to the first communications bus isolator via a dedicated fault bus isolation output of the subordinate controller using a communications line that is different than the first portion of the external communications bus cabling and the second portion of the external communications bus cabling, wherein the subordinate controller is adapted to detect a fault on the second portion of the external communications bus cabling or on at least one of the second plurality of peripheral devices and transmit, via the dedicated fault bus isolation output of the subordinate controller and the communications line, a first signal indicative of the fault to the first communications bus isolator, wherein the first communications bus isolator is adapted to isolate the first portion of the external communications bus cabling from the second portion of the external communications bus cabling by actively disabling the external bus cabling receivers on the second side of the first communications bus isolator when the first communications bus isolator receives the first signal from the subordinate controller, wherein the first portion of the external communications bus cabling and the second portion of the external communications bus cabling are located outside of a control panel enclosure, wherein the first communications bus isolator includes a communications bus repeater, and wherein the communications bus repeater is adapted to automatically pass second signals between the first portion of the external communications bus cabling and the second portion of the external communications bus cabling when detection of the fault on the second portion of the external communications bus cabling or the at least one of the second plurality of peripheral devices is absent.