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I have a Microsoft Surface Pro tablet which, when charging from the included power adapter, gives a slight tingling feeling when touching anywhere on the Magnesium shell.

This is a commonly reported problem with the Surface Pro and Microsoft are willing to replace affected units free of charge.

Out of curiosity, I would like to measure the voltage on the case with respect to ground. The AC adapter is a 2-prong device which uses a IEC standard figure-8/shotgun connector (no ground pin) and outputs both 12V and 5V DC.

If I take a multimeter and connect one lead to ground, and the other to the case of the tablet, will I damage either the multimeter or the tablet? My understanding is that the voltmeter input is a very high impedance and as such a negligible current should flow.

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AC probing is safe so long as your multimeter is rated for the full AC mains voltage you'll be playing with, and the probes that you'll be using are insulation-rated for that voltage as well. Most reasonable-quality multimeters are OK for 120VAC work. Make sure the probe wire insulation doesn't have any breaks in it.

The meter will present a voltage measurement resistance in the megohm range, so there's no real risk of damaging anything (yourself, the meter or the tablet).

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  • \$\begingroup\$ bhillam is in Oz which has 240V AC mains not 120 V. However most reasonable quality multimeters will have at least a Cat-II 600V or 1000V rating. Some of the better ones will actually reach that standard. \$\endgroup\$ Commented Jul 29, 2013 at 9:55
  • \$\begingroup\$ Indeed. You don't want to use a $10 bargain-bin multimeter with falsified certifications for mains work. \$\endgroup\$ Commented Jul 29, 2013 at 13:11
  • \$\begingroup\$ My multimeter is Cat-II 1000V rated. I'm getting some weird readings though so I'll have to try again tonight (maybe I'm missing something) \$\endgroup\$
    – bhillam
    Commented Jul 30, 2013 at 0:36
  • \$\begingroup\$ Weird in what way? Please update your question with whatever weirdness you've found. \$\endgroup\$ Commented Jul 30, 2013 at 1:07
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The case of our Microsoft Surface RT sits at a 9 volt DC offset relative to ground, whilst the reported AC component, sinusoidal or otherwise, of the offset is 95 volts!

Measurements taken whilst the Surface was charging, with a basic digital multi-meter, which while not the absolute last word in accuracy, I know from testing against known reference sources is pretty good in terms of DC, and provides sensible readings when measuring the nominally 240 volt RMS mains.

And yes, you get a sharp tingle from the case when the Surface is running off the mains. More noticeable when you brush with the inside of your arms or wrists as the skin there is presumably thinner, presenting less of a barrier to the flow of current. Running your finger steadily along the casing whilst running from mains yields an odd, slightly rubbery, stuttering sensation. Disconnect the power lead and this changes immediately to the smooth brushing, sliding sensation you would otherwise expect from touching any metal object.

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I noted that the Microsoft Surface Pro adaptor does not have earth and I have read elsewhere that the tingling feeling have two external monitors which I tried connecting to my laptop through a type C to HDMI adaptor. One monitor is powered through a 3-pin plug and another is powered through a 2-pin plug. My observation is that the tingling sensation is felt when the laptops is connected to the monitor powered through a 2-pin plug, while there is no such sensation when the laptop is connected to the monitor powered through a 3-pin plug. My hypothesis is that when the system is connected to a 3-pin plug is connected, the entire system does have a grounding. Hope it is helpful.

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    \$\begingroup\$ What you are describing is Y capacitor leakage. If your monitor requires ground, you must supply it via a grounded outlet. \$\endgroup\$
    – winny
    Commented Jun 19, 2022 at 16:49

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