FIG. 5A is a timing diagram (not to scale) illustrating operation of an isolator when shorts repeatedly occur and are detected by the controller, according to an embodiment. The short circuit occurs at 502, causing the current to increase. At 504, after some delay due to detection by the isolator plus an intentional wait, the isolator opens and the current drops to 0. Shortly after the isolator opens, at 506 the Ptest begins checking whether the short is still present. In this example, the Ptest at 508 detects that the short is gone; the isolator closes, the Ptest is turned off and the current rises to its normal operational value. FIG. 5A depicts a series of intermittent shorts (of which only two are shown), wherein one short may follow another by, for example, one millisecond at 510. The cycle repeats: the next short is detected at 510, the isolator opens at 512 and the Ptest is enabled at 514. At 516, the Ptest determines that the short is no longer present, the isolator closes and the current again returns to its normal operating value. If this cycle of isolate/de-isolate continues, communications along line 130 may be severely disrupted, impacting the ability of the fire detection system to function properly. An embodiment of the invention as described above identifies when this cycle is repeating by tracking the number of repeating shorts (RepShortCntr) that have occurred within a predetermined time frame and causes the isolator to remain open for a duration depending on the value of RepShortCntr.