What is clamping voltage or VPR (voltage protection rating) on a surge protector?

VPR is the maximum voltage allowed to pass through the surge protector during a spike. It’s the voltage level which causes the MOV to “clamp” down on the spike to prevent most of the surge from passing through to connected equipment. MOV’s convert the electrical charge into heat and absorb it so it won’t damage your equipment. When measuring the VPR of a surge protector, the lower the number usually means better protection.