These three-stage surge protectors meet IEEE 1000-4-5: 1995 and IEEE C62.41-1991 recognized standards for premium surge protectors. It protects against lightning strikes, power surges, and other types of voltage disturbances with three stages of protection for each supported line: a gas discharge tube followed by a series resistor and finally a Transient Voltage Suppresser (TVS). Three RS-422/485 signals on terminal blocks are supported with a clamping voltage of approximately 6.8 Volts. <br /> <br /> These surge protectors housed in a tough metal, panel mount case with a protected signal ground connection and dedicated chassis ground lug.In order to work properly, it is important to have a good connection between the #10 screws and a solid earth ground. The BB-485HESP provides two terminal posts and two metal mounting brackets to provide a good ground connection.