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I've tried to turn on my old PC with my old LCD monitor, which is powered by a kettle cable directly from mains, no power supply brick). When trying to get it to work, I have noticed the following phenomena:

1) The VGA connector from the monitor produces electrical sparks against the PC case, even when the PC PSU is switched off (but both are connected to the same extender cord) - See video: https://youtu.be/6Jxlndc2ZUA

2) While bending down to look at the connector (with the VGA cable connected), and touching the PC case with my hand, my head accidentally touched one of the strings on my electric guitar and I felt an electric spark on my head (not very strong but noticeable). The guitar is connected to an external sound card, which in turn is connected via USB to my main PC, which is connected to a different power outlet.

At first I assumed it's some kind of grounding problem on my monitor. So I hooked up some random grounded electrical device I found in the house (the base of an electric kettle) to the same extension cord, and tried to brush the VGA cable against its metal casing while the other end is connected to the monitor. I couldn't see any sparks this time.

I have also tested this the other way - I have connected the VGA cable to my PC, and tried to see if it produced sparks when rubbing the other end against the electric kettle base casing, and nothing happened.

Since I am alive and the sparks don't look too big, I assume the VGA cable isn't really live with 220V but instead something else is going on.

Can anyone suggest an explanation to the above situation?

Update:

I have repeated the experiment using a different wall plug and extension cord, one that I have personally tested with a multi-meter and made sure that is wired correctly regarding live/neutral/gnd.

Turns out that one of the kettle cables I have been using is indeed missing a ground prong, and has a hole instead:

enter image description here

This is meant for sockets that have a ground prong (mine doesn't), so effectively, it wasn't grounded.

I have tested the following combinations:

1) ungrounded monitor, grounded pc (psu off) - VGA cable is arcing against PC casing 2) grounded monitor, ungrounded pc (psu off) - VGA cable is NOT arcing against PC casing.

In this case, I assume there is some kind of issue with the computer monitor. Getting a grounded power cable for it would merely hide the problem, and I should probably replace it.

Is there anything else I should look at before dismissing the issue, just to be safe?

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  • \$\begingroup\$ Could it be that your cables have pinout different from what your computer/monitor expecting? e.g. ground wire going to neutral pin and VV? \$\endgroup\$
    – Maple
    Commented Jun 15, 2018 at 23:38
  • \$\begingroup\$ I doubt it since these two have been working together for a long time. It might have been with a different cable though. \$\endgroup\$
    – eliba
    Commented Jun 16, 2018 at 0:43
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    \$\begingroup\$ what in the world is kettle cable? \$\endgroup\$
    – jsotola
    Commented Jun 16, 2018 at 0:44
  • \$\begingroup\$ I didn't say they could not work. I just pointed out why you might have different ground potential. \$\endgroup\$
    – Maple
    Commented Jun 16, 2018 at 1:16
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    \$\begingroup\$ There (probably) isn't anything wrong with either item. One or both contain power supplies that require a ground connection. If that is absent, the parts that should be grounded, e.g. the computer metalwork, will drift to some voltage (at some impedance) from ground, causing a voltage difference to any part that is grounded. Which makes the sparks. This isn't' "hiding" the problem. It's operating the equipment as intended. \$\endgroup\$
    – Ian Bland
    Commented Jun 16, 2018 at 15:56

2 Answers 2

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All VGA monitors must have Earth bonding. Yours doesn't, so get the right cable or hardwire a frame screw to earth bond screw. (for kiwi's only)

A continuity or line voltage tester or a DMM to check for gnd voltage can be done to isolate the HV problem.

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    \$\begingroup\$ I think the monitor is a red herring. The last time I got minor belts from a PC was due to the PC not being earthed resulting in some kind of voltage appearing on the PC metalwork, which tingled but wasn't full on mains. The VGA cable probably is just acting as an earth, hence the sparks. I strongly suspect the PC PSU or the grounding thereof. \$\endgroup\$
    – Ian Bland
    Commented Jun 15, 2018 at 21:37
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    \$\begingroup\$ If the line and neutral orientation is critical wrt. Missing Earth bond. It can fry fish \$\endgroup\$
    – D.A.S.
    Commented Jun 15, 2018 at 21:49
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    \$\begingroup\$ The kettle cables I'm using have 3 prongs on both sides. Searching on google images yields similar results to what I have and am using. \$\endgroup\$
    – eliba
    Commented Jun 15, 2018 at 21:50
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    \$\begingroup\$ Ok Then you have a ground fault somewhere . Do you have a DMM to measure ground voltages and a known good earth test point? \$\endgroup\$
    – D.A.S.
    Commented Jun 15, 2018 at 21:52
  • \$\begingroup\$ Unfortunately I don't have a multimeter but I will borrow one and run some tests, as suggested in laptop2d's answer as well. \$\endgroup\$
    – eliba
    Commented Jun 15, 2018 at 22:03
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Most likely you have a faulty ground at the first location, or a mains fault inside either monitor or computer. Another thing that could do this is maybe someone connected the power wrong in the wall outlet.

Have an electrician check the wall to make sure it's good.

The best way to measure these is with a volt meter, measure the voltage between the devices, and then between each device and ground (if it really is grounded) if the chassis of either device is more than 0V with respect to ground then that is a faulty device and needs to be replaced. Make sure you follow protocol for handling high voltages and treat each device as a live mains wire because you could be electrocuted.

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  • \$\begingroup\$ I will borrow a multi-meter tomorrow and report back with results. \$\endgroup\$
    – eliba
    Commented Jun 15, 2018 at 22:05
  • \$\begingroup\$ the OP said that the sparks occur even when the PC and the monitor are both connected to the same extension cord \$\endgroup\$
    – jsotola
    Commented Jun 16, 2018 at 0:43
  • \$\begingroup\$ I am sure that of someone connected live to gnd in the outlet it would have been noticed earlier \$\endgroup\$
    – PlasmaHH
    Commented Jun 16, 2018 at 5:34
  • \$\begingroup\$ @PlasmaHH What if you swapped netural and gnd? Another thing that might be happening is maybe the ground has some kind of voltage on it \$\endgroup\$
    – Voltage Spike ♦
    Commented Jun 16, 2018 at 5:42

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