The Calsense TP-1 Transient Protection Board utilizes a bidirectional transient voltage suppressor. This device provides increased protection against high voltage, high-energy transients on the 24 VAC field side of the controller. The Transient Protection Board protects against these transient surges by using transorbs, a solid state device that directs or switches the incoming transient away from the controller to a ground rod. Outdoor installation requires a weatherproof TPB Box.