The history is lost in committee activities from years ago, but I can provide my own thoughts.
The limit for accessible parts on circuits not connected to protective earth is set below the threshold of sensation, since that current is likely to pass through the user in normal use if he touches the part. The limit for hand held equipment is set low enough that if the earth path fails, the resulting shock is not likely to cause someone to drop what they are holding. Note that the higher limits of 3.5 ma for the general case can provide a substantial but not harmful shock under single fault conditions. Bob Johnson ITE <http://www.itesafety.com/> Safety -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of xingwb Sent: Sunday, June 23, 2002 7:57 PM To: [email protected] Cc: Rich Nute Subject: TOUCH CURRENT LIMIT Dear colleagues I have a question regarding touch current limit of IEC 60950? We can read from table 5A of IEC60950:1999: Touch current limit for accessible parts and circuits not connected to protective earth: 0.25 mA question 1 : How does it (0.25mA) come from and what it is based on? based on IEC479? OR other source why it is not 0.5mA(based on IEC60479) question 2 :for hand-held equipment it is 0.75mA why ? Please shed some light for above questions Any comments are appreciated Best Regards Xing weibing 2002-06-24
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