The VCL (Maximum Clamping Voltage) represents the high end of the voltage characteristic curve. It is the peak voltage that will appear across the TVS device during the rated peak pulse current test. However, it is not the highest voltage that could ever appear across the AK device. A shorter pulse with more current would cause a higher voltage than VCL to appear across the device. Not all real world lightning wave forms will follow the industry specifications, nature does not read specs! Similarly, the TVS diode could be destroyed if a voltage lower than VCL but higher than VBR is applied to the device for a sustained period of time. It is important to note that because the AK series are made of silicon, there is no aging mechanism like that found in ceramic technologies like metal oxide varistors. As long as the peak pulse current rating is not exceeded, an AK device will not wear out or degrade over time. The VCL rating in the data sheet therefore is tied very closely to the peak pulse current test waveform. It is a good measure of comparing one overvoltage protection choice against another to get a good idea of their relative performance. This is why the AK series is rated using the same waveform as the MOV devices. Since they share a peak pulse current test wave form their maximum clamping voltages can be compared directly.