Fire alarm cable variation in gauge size and resistance will affect the allowable run length from the panel to the start point of the zone. Protectowire panels are designed to accommodate up to 100 Ohms of feed or interposing cable. The allowable length is 100 Ohms divided by the number of Ohms per unit length (feet or meters) of feed cable. The maximum allowable feed cable length is typically reduced to 18 Ohms when the Alarm Point Location Meter is utilized in the control panel.