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.
Nearly 51,000 deaths and 28,500,000 medically treated injuries were recorded by US Consumer Product Safety Commission in 2019 and 2020, respectively. 1 Governmental regulatory bodies, third-party safety certification laboratories and other jurisdictional authorities help maintain safe product use. This paper provides overview of key regulatory considerations to help achieve safer products.
Current trends in powered wearable technologies show that users are spending more time than ever in contact with their devices. Users now wear devices such as smartwatches and fitness trackers up to 24 hours per day to make use of ubiquitous health, exercise, and sleep-tracking features. Long duration contact with these heat dissipating devices increases the thermal dose delivered to user's the skin tissues. Methods for accurate, real-time prediction of the time-temperature response of the skin based on device heat dissipation and external conditions are needed to characterize and monitor the thermal dose received by the user. This article presents methods for building reduced-order models (ROMs) based on proper orthogonal decomposition (POD) for modeling transient heat transfer in partially-perfuse tissue in prolonged contact with a heat-generating wearable device. ROMs generated using this methodology are able to provide fast, accurate temperature forecasts for arbitrary time-varying boundary conditions, heat sources, and environmental conditions given an appropriate set of training data. The solution of these reduced-order models is shown to be over an order of magnitude faster than a finite-volume implementation of the same scenario, even in one spatial dimension.
