Overview
IEC TR 60479-5:2007, published by the International Electrotechnical Commission (IEC), addresses the effects of electric current on human beings and livestock, specifically focusing on touch voltage threshold values for physiological effects. This technical report provides guidance for technical committees and safety professionals on determining acceptable combinations of touch voltage and exposure duration to limit physiological risks, based on analysis of body impedance and effects of current flow. The thresholds discussed are derived from established data in IEC/TS 60479-1 and adapted to account for uncertainties and environmental conditions.
Key Topics
- Touch Voltage Thresholds: The report sets forth a systematic approach for identifying voltage-duration combinations that may trigger physiological effects when humans or livestock come into contact with electrified conductive surfaces.
- Current Pathways and Body Impedance: Emphasis is placed on various current pathways (such as hand-to-hand or hand-to-feet), and how body impedance varies based on contact conditions and environmental factors.
- Environmental Conditions: Threshold values are provided for different scenarios, including dry, water-wet, and saltwater-wet skin, taking into account contact area and moisture, which significantly affect body impedance and resultant risk.
- Physiological Effects: The document categorizes risk thresholds for key physiological responses such as startle reaction, strong muscular contractions (including inability to let go), and ventricular fibrillation.
- Voltage Types: Only 50/60 Hz sinusoidal alternating current (AC) or pure direct current (DC) without significant harmonic or superimposed components are considered.
- Guidance for Committees: Touch voltage-duration threshold recommendations are intended as a technical foundation for setting safety limits in diverse applications.
Applications
IEC TR 60479-5:2007 has practical value for many sectors where electrical safety is a priority:
- Standards Development: Technical committees use the voltage-duration thresholds to define safe touch voltage limits for products and installations, in line with risk assessment practices.
- Electrical Equipment Design: Designers employ these thresholds to ensure that accessible conductive parts cannot deliver hazardous current levels under normal or fault conditions.
- Occupational and Public Safety: Safety professionals reference these values to develop protection strategies for workers and the general public, particularly in environments where accidental contact with live parts is possible.
- Risk Assessment: The report supports comprehensive risk assessments by providing scientific criteria to evaluate touch voltage hazards under specified contact and environmental conditions.
- Product Certification and Compliance: Manufacturers and testing organizations use these values as benchmarks for compliance with international electrical safety standards, helping to ensure the reduction of electrical shock risks.
Related Standards
For a holistic understanding and application, IEC TR 60479-5 is best used in conjunction with the following IEC standards and technical specifications:
- IEC/TS 60479-1: Effects of current on human beings and livestock - General aspects (primary reference for current thresholds and body impedance values).
- IEC 60050-195: International Electrotechnical Vocabulary - Earthing and protection against electric shock.
- IEC 60990: Methods of measurement of touch current and protective conductor current.
- Other parts of the IEC 60479 series: These provide further detail on specific applications and considerations relating to electric shock.
Practical Value
By providing scientifically based touch voltage threshold values, IEC TR 60479-5:2007 enables:
- Informed decision-making about the design and installation of electrical systems.
- Enhanced personal safety through targeted protective measures.
- Efficient risk management in both high- and low-voltage installations.
Using IEC TR 60479-5:2007 as a reference supports the adoption of best practices in electrical safety, promoting harmonized protection for people and animals across different regions and industries.