Hi all..... >From data presented in a Stanford University course on Electronics in Medicine approximately 20 years ago, heart fibrillation could be induced by passing only 1 mA directly through the heart muscle. When considering all the parallel current paths around the heart for an external exposure to a (potentially lethal) source voltage, the dangerous current threshold could easily vary from 5 mA (e.g., for a connection between a person's two hands) to hundreds of millamperes, depending on the source and return connection points on the body.
Because of this potential range of current, some standards group has made a subjective judgement (5 mA for US GFIs) that many other groups would not have made. If not prohibitively expensive because of inadequate technological solutions, it's better to be on the safer side of low trip currents. I agree with an earlier comment about the infrequency of nuisance tripping; i.e., low current thresholds are NOT a problem unless the circuits are degraded in the first place. Just my two cents worth, Mike Conn Owner/Principal Consultant Mikon Consulting
