🚀 go-pugleaf

Paul E. Schoen wrote:
> "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.

I did try immediately afterwards (after plugging it in again for a bit). 
Couldn't see much. But it may be a time issue - it's possible to get 
one's hands onto the pins rather more quickly that a pair of multimeter 
probes. Depends how long the capacitor would remain charged with no 
output load.

Further experiments using my hand might be informative, but I'm not game.

Sylvia.