IEC 61000-4-2 calls for neutralizing the test article for ungrounded equipment where a discharge event fails to occur. This process is based on the premise that a residual charge is present when the next discharge trial is applied and the residual charge adds to the subsequent event voltage. This could result in testing at an unknown value potentially higher that the specified voltage. The residual charge will dissipate over time but it could take several seconds for complete neutralization especially if testing in a low humidity environment.
To meet the standard, testing should include a neutralization process to conform to the test standard. This is accomplished by using a conductive cloth or brush through a resistive connection to the ESD simulator ground reference.
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