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My external hard drive came with a 12V 1.5A two-pronged Switching adapter for powering itself. But as with 90% of switching power supplies, the output isn't isolated. If you touch the output (supposedly 12V) you can feel a mild tingle. The leakage current is too faint for multimeters to detect, but my high-sensitivity line tester reports it at around 90V (220V line voltage).

Well, I do not think it is a problem with the adapter because my laptop's power adapter does this too IF I do not connect the grounding pin to the wall socket. And so do almost all of the switching power supplies that power my devices, with the third, grounding pin disconnected.

This leakage current mightn't cause immediate problems, but I'm sure it's harming the computer's sensitive components in some or the other way. So I want to ground the Hard Drive's power adapter. Is it as simple as connecting a grounding wire from the wall to the negative terminal of the output? Will doing this harm the adapter? I checked my laptop's adapter with a multimeter, but the ground pin and the output aren't directly connected. So I am confused. Could you please help?

  • Out of curiosity, what is the model of "high-sensitivity line tester" that shows you 90V ? – Nick Alexeev Nov 27 '15 at 01:34
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    I'm not sure why you think this will be a problem... –  Nov 27 '15 at 02:03
  • Line tester @Alexhttp://www.urjakart.com/taparia-digital-line-tester.html –  Nov 27 '15 at 02:06
  • @Bagho I doubt that this this tester is more sensitive than a multimeter. The former doesn't even have a return connection (I don't see it). – Nick Alexeev Nov 27 '15 at 07:00
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    "But as with 90% of switching power supplies, the output isn't isolated" - what you have said is just not true - of course it isolates and uses a transformer - do you think the 1.5 A is coming direct from the AC input via some 200 watt/VA dropper circuit? –  Nov 27 '15 at 10:07
  • "I checked my laptop's adapter with a multimeter, but the ground pin and the output aren't directly connected. So I am confused." Maybe because it IS isolated, like 90% of the power supplies are? (just to throw a number out without any reference) –  Nov 27 '15 at 10:20
  • Andy: Not really. They use a transformer of course. I'm curious myself why most switching power supply leak, though. A correctly built linear power supply doesn't, right? Is it because of the close proximity of high voltage and low voltage components in a switching power supply? –  Nov 27 '15 at 11:07

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