Impulse voltage versus RMS, versus VDC

[sunnydaze]

Hello,

The below link describes National Instruments interpretation of CAT I - CAT V meanings. I've pasted an example from their paper that has me a little confused.

Can someone explain how they get the 2,500 V impulse voltage in the below example?

Thanks
Mike

http://www.ni.com/white-paper/5019/en/

Maximum switching voltage

Channel-to-ground.................................300 V Category II, 600VDC, V ACpk Category I.

Using the chart below we deduce the following: This specification informs the user this module is rated for 300V CAT II and 600V CAT I. In other words, this module can withstand up to 2,500V impulse voltage.