Bathroom cabinet electrical shock?
Andy Wade wrote:
On 12/05/2011 09:04, Ret. wrote:
[...] When my wife's iPod is on charge (using a non-Apple compatible
charger), if you pick it up and run your finger lightly over the
metal surface, there is also this 'buzz' sensation. I wouldn't
describe it as an electric shock - just a very very mild 'tingling'
sensation.
These 'tingles' are usually the result of capacitive leakage between
the mains and the case of a Class 2 ('double insulated') appliance.
The relevant safety standards usually allow up to to 0.5 mA leakage
at 50 Hz (more at higher frequencies). It's completely harmless[*]
but can be annoying and/or worrying. (The 'return' path for the
current is via the body's natural capacitance to earth, typically a
few hundred picofarads.) It's becoming more common with the move
away from iron-cored transformers to switch-mode circuits in
wall-wart PSUs - a consequence of the WEEE and EuP directives.
With a high impedance voltmeter (any DMM these days) you'll typically
measure 100 volts or more between the case and earth. The source
impedance of these errant volts is very high though, and just touching
the case will lower the touch voltage considerably. Temporarily earth
the case via (say) a 10k ohm resistor and measure the voltage across
the resistor if you want to get an idea of the available touch
current.
As the output of the charger is low, I am assuming that there is no
danger from this...
Unless there is a fault, no.
[*] One case to be aware of is where several items of Class 2 AV
equipment are interconnected by the signal wiring. Here the available
leakage touch current will add up and can reach dangerous levels (3.5
mA is considered dangerous, 10-15 mA can be lethal). Earthing the
system (either directly or via a resistor) is advised in such cases.
Thanks for that.
--
Kev
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