I just wanted to learn some differences between volts, amps, ohms and so forth and came up with this question. If your skin has 100k ohms resistance and the outlet is 220v wouldn't the current flowing through your body be 0.0022 amps?
Answer
In Europe the rule is generally 60V DC is safe for casual contact with live conductors. Read what the IEC says: -
The International Electrotechnical Commission (IEC) has issued several reports on electrical safety. The IEC “Electrical installations of buildings” report (IEC 60634-4-41:2001) specifies that for unearthed circuits “if the nominal voltage does not exceed 25 V a.c. r.m.s. [35 VPEAK] or 60 V ripple-free d.c., protection against direct contact is generally unnecessary; however, it may be necessary under certain conditions of external influences (under consideration).” For earthed circuits the IEC considers protection unnecessary when “nominal voltage does not exceed 25 V a.c. r.m.s or 60 V ripple-free d.c., when the equipment is normally used in dry locations only and large-area contact of live parts with the human body is not expected; 6 V a.c. r.m.s. [8.5 VPEAK] or 15 V ripple-free d.c. in all other cases.”
Extract taken from this document.
The sort of voltage level talked about in the extract isn't generally believed to sufficiently break down the skin's "high surface resistance" BUT, mains voltages are lethal because they DO break down the surface resistance and then you just have the body's internal resistance and this is only a few hundred ohms. With (say) 220V AC applied, the current can be greater than 100mA and this is really problematic: -
NEW SECTION:
An interesting and related spin off subject is the well-known effect of a human body damaging electronic circuits by static discharge. The human body is modelled as a capacitance to earth of about 100 pF. This capacitance is charged up to several kV and the discharge path into the electronics under test is via a current limiting resistor.
An important thing to note is that unless the human body directly connects to earth (a rarer situation than normal), the current flow due to touching a live wire is somewhat limited by this capacitance.
This document entitled "Measurements upon Human Body Capacitance: Theory and Experimental Setup" concludes that about 160 pF is a the human body capacitance in the following experiment: -
So if we connect to 220V 60Hz, 160 pF has an impedance of 16.6 Mohms (reactive) and would cause a reactive current of about 13.3 uA. I don't think capacitive effects are going to be very significant.
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