🚀 go-pugleaf

"Sylvia Else" <sylvia@not.at.this.address> wrote in message 
news:00b8a4ce$0$7243$c3e8da3@news.astraweb.com...
> J.A. Legris wrote:
>> On Mar 8, 10:35 am, Sylvia Else <syl...@not.at.this.address> wrote:
>>> Sylvia Else wrote:
>>>> I've recently bought a D-Link DIR-300 wireless router. While
>>>> disconnecting its power supply from it, I got a tingling sensation 
>>>> when
>>>> I touched the plug (to be clear, I'm talking about the 5V DC plug, not
>>>> the mains plug).
>>>> An AVO meter shows about 90V AC to earth from either side of the 5V
>>>> plug. Short circuit current to earth is about 0.1mA.
>>>> Still, I thought these things were meant to be completely isolated. 
>>>> Has
>>>> there been a change of approach?
>>>> Sylvia.
>>> Apparently it's normal, and is related to RFI suppression.
>>>
>>> Sylvia.
>>
>> Just think, the only thing between you and the great beyond is a thin
>> layer of ceramic material, possibly contaminated with who-knows-what,
>> bearing a certification logo of dubious authenticity. It's time to
>> invest in some rubber-soled slippers.
>
> It's certainly not a happy thought. I will be treating the low voltage 
> side of such power supplies with more respect from now on.
>
> BTW, I tried the same tests with the power supply for my cable modem. It 
> showed higher voltages, but lower current.
>
> But immediately after I'd unplugged it from the mains, I happened to 
> touch the mains plug pins with the palm of my hand, and got a significant 
> shock off it. Reverse leakage through the rectifiers? But why should 
> there even be enough to feel?

100 uA is usually below the threshold of sensation (usually about 1 mA), 
but some people can sense current of lower value. If it has a three prong 
plug, it may have capacitors to ground. There is also some capacitance from 
the primary to secondary windings, especially if they are layer wound. The 
shock you got from the plug after disconnecting from the mains may have 
been from an RFI filter capacitor that was still charged. If you touched 
across two blades of the plug, that might explain it. If you only touched 
one blade, then there must have been another return path to ground, such as 
the secondary output to a chassis ground, and you would have had to touch 
something else grounded, or be wearing very conductive shoes. If it is a 
switching supply, there is a fairly large electrolytic charged to about 180 
or 360 VDC, and maybe there is reverse leakage through the bridge 
rectifier. You might check for DC voltage on the mains plug blades after 
disconnection.

Paul