The rated impulse voltages used in IEC 664-1 are to my knowledge based on statistical data from various installations word-wide. The classification according to Overvoltage Catergories I-IV is in accordance to IEC 364-4-443. In the example OV Cat. IV would be at the origin of the installation (eg. a electricity meter). Usually IT equipment is Overvoltage Cat. II. If within the equipment no higher voltages than the working voltage (1000V in the example) are generated, the test voltage would be 8.000 V. This is the highest mains transient that would be expected to enter the equipment. Since this was measured with the working voltage (1000V rms) present, I assume this voltage has not to be added on top of the 8.000 V.
>I am trying to understand the requirements and the rationale behind the >Insulation co-ordination Impulse tests of IEC664, IEC1010-1, etc. > >Were these impulse levels determined by testing? >If so does a report on the testing exist in a location that I can access? >I assume testing was done and a multiplication factor was applied to the >maximum value found. > >Are the impulse test levels defined peak from ground, >or peak value added to the power sinewave at 90 and 270 degrees? >Another way of asking this is, in testing for a 1000 V, CAT III circuit, >is it 8,000 volt peak impulses, or 8 KV plus 1,414 V = 9,414 V peak? > >Any input would be greatly appreciated, either directly or through this >great network. >Thank you in advance. > >Wayne Thomas >Tektronix > Mit freundlichen Gruessen/Best regards, Volker Gasse
