Here is the install manual for the RSH-50. 

The RSH-50 works by absorbing the surge. Since its tied to the front of unit electrically it allows that surge protector to absorb the surge before it enters the rest of the system. Electricity will always take the shortest path. Good for furnaces and air conditioners and heat pumps. If you are installing a minisplit or any other type of inverter, consider the 96421, or the 96424 which also feature a line voltage monitor.