ESF-Report No. 6E

A new approach to protection against harmful electric shock based on tolerable risks and fault protection by automatic disconnection of supply for a.c. 50/60 Hz and for d.c. (2008)

Authors: H. Bachl, G. Biegelmeier†, R. Hirtler and A. Mörx

Summary

In this report a new approach to protection against electric shock is proposed based on holistic considerations with clear conventional agreements for tolerable and non tolerable risks of harmful electric shock. This approach has become possible due to considerable progress achieved in electro-pathology during the last decades.

The procedure for the derivation of time/current zones Z1 (AC) and Z2 (AC) as well as Z1 (DC) and Z2 (DC) for tolerable and non tolerable risks of harmful electric shock is explained. They are based on the results of fibrillation experiments with sheep, dogs and hogs. In addition the results of experiments with corpses and human hearts and that of experiments with dead hogs and hearts of dogs are taken into account. For establishing suitable disconnection times for automatic disconnection of supply in low voltage installations various current paths in the human body for final and distribution circuits in low voltage installations are considered. The same criterion for the risk limit as used for decades, namely ventricular fibrillation, is conventionally taken for defining the time/current zones.

As an alternative to the requirement to consider certain disconnection times a simple method using disconnection current factors is proposed.

Furthermore, with the new approach the advantages and disadvantages of TT- and TN-systems concerning fault protection can be explained easily.

 

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