What is the significance of the Maximum Continuous Operating Voltage (MCOV) when considering a surge protector?
Surge protectors fail for one of two reasons; a surge that exceeds the current capacity of the unit or a swell in the line voltage supplied by the utility. Surge protection components have a voltage level at which it changes state to a low impedance path. This is the MCOV. The component MCOV selected by surge manufactures for their products is typically 1.15 the nominal service voltage, as the power companies usually promise AC power will be nominal +/- 10%. In developing countries, the utility power can swell, for short periods, way above the +10% value. When this happens, the surge protectors conduct and start to carry line current, heating up and going into thermal runaway, until failure. This means that the surge protection on a site fail because of the utility power swells, unrelated to surges, and is often not covered by some warranties. A higher MCOV generally implies a higher let-through voltage. Some manufactures use large block MOV components with higher MCOV’s, but the large
