Comment by BJBBB | Hacker News Reader

Comment by BJBBB | Hacker News Reader

Geez peoples - so much misinformation. Touch current test methods and limits are well-defined through out the world. Poor power 'quality' may affect this measurement, but is not a significant contributor to the magnitude of potential leakage through the ground wire or through exposed metal surfaces. It is a function of the power conversion equipment connected to, or internal, to the device. Even where wiring does not meet code, the upper limit to this measurement is well defined per the simulated fault conditions required in the test methods.

People that claim to be engineers need to read and understand the basic physics behind the product safety standards scoped by your equipment. For EU, code is defined in BS7671/IEC60364; and NFPA70 (mostly article 250) in the U.S.; and similar stuff in C22.1 for Canada.

ITE power supplies must meet the locally harmonized version of IEC60950-1 (soon to be obsoleted by IEC62368-1). Where there is no ground pin, North American power supplies must meet UL1310/CSA No.223. These standards all have specific limits for voltage, current, and VA levels that can be exposed to the end-user, for both normal and abnormal operating conditions.

> Where there is no ground pin, North American power supplies must meet UL1310/CSA No.223

So, as far as I can tell, with a brief skim of the standard, a class 2 device should have no more than 0.5 mA leakage current, right?

I just measured the leakage from my macbookpro through my body to ground and it's about 50 μA. Well within the limits.

So I guess that's why they never did anything about it. Still amazing that you can clearly feel this current: if you lightly brush your wrist around the sharp edges it actually hurts. I wonder how 500 μA would feel.

Depends on the 'bandwidth' of the signal and the test equipment and the individual. Generally consider many non-medical measurements below 025mA suspect, as few design engineers make an effort to understand the various frequency components of the voltage and current leakage signals, and/or understand the effects to the signal of instrument impedances.

Have had several discussions with Mr.Pete Perkins (he sits on several STCs and has written several IEEE papers) on this subject, and we agree that the human body model referenced by these safety standards being used for the measurement network (IEC60990) have problems because the medical community does not understand physics. As the various standards committees continue to look at the body of work being done by bioengineers, will probably see better measurement methods being codified.

Human response and perception to electricity has significant variance and resultant effects/affects. My wife can detect less than 10uA at 200Hz/42V. My detection threshold is at least an order of magnitude greater, even at 50Hz.

Need to correct some stuff.

Class 2 (arabic numeral) is for limited power sources, regardless of construction class.

Class II (roman numeral) indicates a construction class where safety cannot be dependent on a ground bond.

Class I (roman numeral) indicates safety is dependent on a reliable ground bound.

Class I equipment, depending on the scoped end-use equipment safety standard, can have up to 25mA of leakage.

Class II equipment, depending on the end-use environment, can be limited to 0.25mA of available touch leakage.

A good reference for Class 2 and 3 equipment is the UL5085-x series (same as CSA No66.x).

For the EU, there are no harmonized standards in the Low Voltage Directive that have an equivalent Class 2/3 construction, although there are several safety standards that address requirements for 'inherently limited' power sources.

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