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We purchased a second hand NEC desktop computer and just lately we had a long beep problem that occurred. I figured it might be the RAM, so I disassembled the system unit and cleaned the RAM. However, there is an instance when I plugged it all in again and experienced some electric shocks on the case.

Everywhere I touched has this electricity so I immediately shut it down. I know static electricity might affect the motherboard that's why I am quite worried. I checked the plugs and found out that it was 3 prong plug but the ground is missing. I am not sure if the previous owner just cut it down or it just had a space available to input ground (not sure if this is a thing though).

I am thinking of buying a 3 prong plug and replace it but I am not sure if that would be safe. I am aware that every unit is designed specifically whether it needs to be grounded or not. That is why every single one of them comes with a different plug type.

Would replacing the plug a good idea and will prevent future instance of this issue?

Can someone enlighten me more about this?

Any help would be appreciated. Thanks in advance.

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  • \$\begingroup\$ What country are you in and did you test to see if the third prong actually goes anywhere on the PC? Is there voltage on the case when you plug it into a socket in a different building? \$\endgroup\$ – DKNguyen Nov 9 '20 at 1:57
  • \$\begingroup\$ @DKNguyen Im from the Philippines and havent tried to plug it on a different area. Do all the outlets we have at home have the same voltage? \$\endgroup\$ – ros_beginner Nov 9 '20 at 1:59
  • \$\begingroup\$ The normal ones do but the ones for things like stoves and laundry machine are different and look different. \$\endgroup\$ – DKNguyen Nov 9 '20 at 2:03
  • \$\begingroup\$ @DKNguyen Do you think replacing the plug would make any difference? \$\endgroup\$ – ros_beginner Nov 9 '20 at 2:08
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    \$\begingroup\$ What you're probably feeling is the switching power supply's EMI filter making the case "float" at roughly 1/2 of the AC line voltage. Without a ground, it's free to do that. With a ground, it doesn't, and that also completes the EMI compliance. Plus, if something goes wrong inside that would have made the case completely "hot", the ground connection will trip the breaker instead of killing you. \$\endgroup\$ – AaronD Nov 9 '20 at 2:25
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It's unsafe without the ground pin! You need to cut that damaged plug off and throw it away. And NEVER remove a ground pin yourself. The 2- to 3-prong adapters are meant to provide a ground via the tab and a screw, not to remove it.

What you're probably feeling is the switching power supply's EMI filter making the case "float" at roughly 1/2 of the AC line voltage. Without a ground, it's free to do that. With a ground, it doesn't, and that also completes the EMI compliance. Plus, if something goes wrong inside that would have made the case completely "hot", the ground connection will trip the breaker instead of killing you.


Like Chris Stratton said in a comment to the question, your outlets may also be dangerously miswired. A common form of that in the U.S. is called reverse-polarity-bootlegged-ground, where:

  • The ground and neutral that are supposed to run independently back to the distribution panel, are instead tied together at the outlet and a single shared wire runs back for both. That's a bootlegged ground, and is hazardous enough already by itself.
  • In addition to that, the hot and neutral wires are also swapped. If they're both black, like in old wiring in the U.S., or otherwise don't have a color code, then that's an easy mistake to make.

The combination of both factors gives you a ground pin that is connected to AC hot, in a way that a casual plug-in tester will NOT catch! Touch that and a real ground at the same time, and you complete the circuit!

You say you're in the Philippines, so the standards might be a little bit different there, but physics still work the same for everyone. Take the principles that I described and apply them to your standards.

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