Lightning Protectors

A surge protector works by clamping the transient surge voltage to a safe level and directing the excess energy to ground. They are composed of two parts: a switching device or circuit and a good ground connection. Design and choice of a power surge protection device is a challenge because the nature of the event responsible for the surge is unpredictable. A strike might be close or far. The surge can arrive with a wide variation in energy magnitude and temporal behavior. 

Optical-Isolators

There is a misconception that optical isolators and surge protectors are the same thing. That is not so. Whereas surge protectors re-direct excess energy to ground, optical isolators block unwanted currents originating on one side from reaching the other side. Optical isolators are designed to eliminate ground loops. A ground loop is a current across the cable created by a difference in potential between two grounded points.