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I bought two cheap monitors in a local shop. They are basically the same model, and both came with an ungrounded external power supply.

After getting a few shocks from the HDMI cable I realized it is outputting a constant voltage. I measured the ground casing of each cable coming out of the monitors with a multimeter and both registered around 1 V (it seems to be actually fluctuating a bit, or my multimeter rods are not very good).

The outlet where I plug my computer is grounded, so I think I can assume this current goes all the way to earth once I connect the HDMI to my computer. I had some instability problems before though, my computer seemed to be not giving the performance it should and I was getting frequent BSOD's. Long story short, I determined that the PSU was the problem, I replaced it, and the computer got back to normal. But I wonder now if this isn't damaging my computer on the long run. I also work with a Mac Mini that is not grounded (or I guess it has an internal PSU that should handle that), connecting these monitors to it makes the whole thing live and everything else that is connected to it. Any insight will be greatly appreciated!

Monitor models:

Monitor 1:

  • Product Name: Athen V2L 21
  • Model: PG-ATHV2L21-BL01
  • Certifications: FCC, CE

Monitor 2:

  • Product Name: Horizon Z21
  • Model: MCR-HZN21-BL1
  • Certifications: TÜVRheinland

PSUs (both are exactly the same):

  • INPUT: 100-240v~50/60hz 0.85A Max

  • OUTPUT: 12.0 V - 2.5 A 30.0 W

  • Certifications: FCC, CE, CB

  • The "certifications" I included solely based on what I saw on their back labels.

  • My AC is 220 V.

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  • \$\begingroup\$ "It shocks you.... and makes the whole setup live" The first and most important piece of advice is stop using it. This is dangerous and abnormal behavior. Yes, there is a good chance of getting hurt and yes there is a good chance of blowing out equipment. \$\endgroup\$
    – MOSFET
    Commented Apr 5 at 19:22
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    \$\begingroup\$ @MOSFET The power supply is likely just equipped with 2-prong ungrounded mains inlet. Perfectly normal these days. I would refuse to buy such a thing though and prefer monitors with grounded mains inlets. Most likely the description about there being constant 1V is wrong too, I'd expect several tens if not hundred volts of AC. \$\endgroup\$
    – Justme
    Commented Apr 5 at 19:38
  • \$\begingroup\$ I'm aware that 2-prong class II insulated devices are very common these days. My concern wasn't 2 prongs vs. 3 prongs. It was that the device (2 or 3 prong, doesn't matter) is shocking you! That's not intended by design (hopefully). Either the device is defective or it has a bad EMI capacitor that is leaky and coupling HV to the LV across an isolation barrier. Does the device have any UL, CSA, CE, or other agency certifying it? \$\endgroup\$
    – MOSFET
    Commented Apr 5 at 19:45
  • \$\begingroup\$ @Justme the fluctuation I talk about is a variation from 0.01 to 1v. But as you suggested in your answer, it is probably discharging when I test with the multimeter rods and goes down to these values. MOSFET Thanks for mentioning these regulators, I will be sure to check those and definitely gonna put these monitors models on the post. \$\endgroup\$
    – Ariel
    Commented Apr 5 at 20:55

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That is annoying but normal these days for equipment with 2-prong mains plugs. There are power supplies that either shock you or don't.

The voltage is high but current is safe as it should be few hundred microamps tops for safety. It is capacitive leakage.

It should pose no danger when the monitot and PC are connected together. The only thing to avoid is connecting (plugging or unplugging) them while being supplied with mains.

If there is any break in the ground connection and only data pins make contact, it may damage either the monitor or PC.

Doing so approximately equals discharging a couple of nanofarads charged to about 100V through the data pin, which isn't normal.

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  • \$\begingroup\$ I now regret buying these monitors, I guess I should always remember to plug my computer to the outlet (since it is grounded), before connecting the hdmi cables. In the case of the mac mini, I suppose there is nothing to be done beyond buying a new monitor that has the 3 prong plug. Thank you for your answer. \$\endgroup\$
    – Ariel
    Commented Apr 5 at 20:49

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