Hi Bob You wrote: > I am looking for any reference(most likely European) which stipulate > 24Vac as a maximum touchable/safe voltage. I have found some references in > regards to 24Vac as a max. in wet or damp locations in mines and quarries(UK > regs.) but have been unsuccessful in finding this limit stipulated in regards > to electrical safety under normal conditions.
It's not a direct answer to your question, but IEC 479-1 : 1994 Effects of current on human beings and livestock, shows that 200mA a.c.for 10mS and 10mA for 2 secs and indefinitely have no harmful effects (fig 14). This, taken into account with Table 1, Total Body impedance, a.c., hand to hand, (95% of the population = 6100 ohms) give a short term (10mS) touch voltage of rather greater than 220V, and an indefinite touch voltage of about 50V. (approx 2-4 times higher for d.c). I'm not aware of a National Standard that specifies 24Va.c. as a touch voltage (wrt ground), though many commercial standards, e.g. machine tools, spec 24Va.c as the maximum volts for control systems, but NOT accessible terminals. I'd worry about the source impedance, 24V a.c. from a 2VA transformer is quite different to 24V a.c. from a 1kVA transformer, just try catching your wedding ring across those terminals and you'd see why! I'll be interested to see how this thread turns out. Cheers, Chris Dupres EMC Specialist. VG Microtech. [email protected] tel +44 (0) 1825 761077 fax +44 (0) 1825 768343 'Opinions expressed are personal, not necessarily Corporate'
