DIFFERENCE BETWEEN CLASS 1 LIGHTNING CURRENT AND CLASS 2 SURGE CURRENT

It is important to understand the difference between class 1 current (lightning) and class 2 current (surge). The following figure 2 illustrates the difference which lies in the time duration of the transient which will determine the power or amount of energy in the transient.

Class 1 = 10/350us from zero to peak takes 10us (microsecond us =10־6 or 10 millionths of a second) and 350us to 50% of the tail of the transient.

Class 2 = 8/20us from zero to peak takes 8us (microsecond us =10־6 millionths of a second) and 20us to 50% of the tail.

This simply means that a 10KA (10/350 class 1) arrester can dissipate 18 times (1800%) more current than a class 2 10KA (8/20 class 2) arrester. Therefore a class 2 arrester in a class 1 area is ineffective and will fail and this failure can be violently explosive. Figure 2 shows clearly that the class 1 waveform carries a huge amount more energy than the class 2 for the same current value.