Hi Vincent:


You asked:


2) Why is there no uniform values for SELV? Example: SELV is defined as voltage 
not exceeds 25Vrms and 30Vrms for IEC 60601-1 and IEC 60950-1 respectively. 


SELV is not a voltage but a scheme for protection against electric shock.  I 
think you are asking why aren’t TOUCH VOLTAGES uniform among standards?  


Touch voltage is defined in IEC TS 61201.  For ac, touch voltage varies from 15 
volts to 55 volts and depends on contact area and moisture of the contact.  
Touch voltages are derived from IEC TS 60479-series and are calculated from the 
body impedance and the current.  


30 volts is for dry contact, 1 cm2.  25 volts is for wet contact, 1 cm2.  In a 
medical environment, wet contact may be expected.  


Best regards,







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