device that contains at least one nonlinear component that is intended to limit surge voltages and divert surge currents

NOTE: An SPD is a complete assembly, having appropriate connecting means.

 

SPD having no intended series impedance

NOTE A one port SPD may have separate input and output connections.

 

SPD having a specific series impedance connected between separate input and output connections

 

SPD that has a high impedance when no surge is present, but can have a sudden change in impedance to a low value in response to a voltage surge

NOTE Common examples of components used in voltage switching type SPDs are spark gaps, gas tubes and thyristors. These are sometimes called "crowbar type" components.

 

SPD that has a high impedance when no surge is present, but will reduce it continuously with increased surge current and voltage.

NOTE Common examples of components used in voltage limiting type SPDs are varistors and avalanche breakdown diodes. These are sometimes called "clamping type" components.

 

SPD that incorporates both, voltage switching components and voltage limiting components.

The SPD may exhibit voltage switching, limiting or both

 

SPD tested according to Class II tests which changes its characteristic to an intentional

internal short-circuit due to a surge current exceeding its nominal discharge current In