What is Voltage Protection Rating (VPR) per UL 1449?

A rating selected from a list of preferred values as given in the latest revision of ANSI/UL 1449. The value of VPR is determined as a higher value taken from table of UL 1449 to the average measured limiting voltage determined during the first set of measured limiting voltages tests during the transient-voltage surge suppression test using the combination wave generator at a setting of 6kV, 3kA. As a standardized rating system, VPR allows the direct comparison between like SPDs (i.e. same Type and Voltage).