What do VPR and MCOV mean, and why are they important specifications?

VPR (Voltage Protection Rating): This is a key performance indicator defined by the UL 1449 standard. A lower VPR value signifies better clamping performance, meaning the SPD can limit the surge voltage to a lower level, providing superior protection for downstream sensitive electronic equipment. For example, for a 120/240V system, a lower L-N VPR (e.g., 600V) is preferable to a higher one (e.g., 1200V).

MCOV (Maximum Continuous Operating Voltage): This is the maximum RMS voltage the SPD can safely endure continuously. The MCOV rating of the chosen SPD must be higher than the nominal voltage of the electrical system it is protecting. For example, for a 120/240V system, the L-N MCOV should be 150V or higher. Using an SPD with an MCOV that is too low (e.g., installing a 120V-rated SPD on a 240V system) will cause the device to fail instantly due to continuous overvoltage.