UL 1449 Voltage Protection Rating (VPR)
As defined by NEMA: A rating per the latest revision of ANSI/UL 1449, signifying the “rounded up” average measured limiting voltage of surge protective device (SPD) when the SPD is subjected to the surge produced by a 6 kV, 3 kA 8/20 μs combination waveform generator. VPR is a clamping voltage measurement that is rounded up to one of a standardized table of values. The standard VPR ratings include 1000, 1200, 1500, 1800, etc. As a standardized rating system, VPR allows the direct comparison between like SPDs (i.e. same Type and Voltage).
Application definition: A measure of an SPD’s let-through voltage or residual voltage, which is the maximum voltage an SPD will let through to a connected device (load) after SPD has performed. The lower the VPR number, the better the protection.