Electrical Shock Stimulation for Complex Leakage Current Waveforms

Leakage or touch current tests for electrical shock protection is mandated by safety standards in the process of issuing a safety certification for various electrical products. UL 101, the UL Standard for Safety for Leakage Current for Utilization Equipment, specifies leakage current limits and testing requirements and procedures used in UL end-product standards. IEC 60990, Methods of measurement of touch current and protective conductor current, is a similar standard used by IEC and IEC-based UL end product safety standards as a reference for touch current testing. Currently, UL 101 uses Root-Mean-Square (RMS) values for the leakage current limits, but IEC 60990 uses the peak value. The ratio between peak and RMS limits is based on pure sinusoidal waveforms, and the peak value is always 1.414 times that of the RMS value. For non-sinusoidal waveforms with higher crest factors, the ratio of RMS and peak limits are no longer related by this constant factor. In some circumstances, a product can meet the RMS limit but fail according to the peak limit when the crest factor for the leakage current waveform is significantly over 1.414. Little research has been done to study which parameter is the better one in terms of defining the electrical shock sensation for non-sinusoidal waveforms. In this paper, electrical shock sensation experiments were conducted for a complex waveform composed of a combination of 60 Hz and a higher frequency sinusoidal signal. The measured RMS and peak current are compared to the 60 Hz only equivalent signal with the same sensation. The deviation percentage is calculated and compared for RMS and peak. The results from an initial and limited experimental investigation showed that peak measurements aligned with perceived sensation more closely than RMS measurements.