just brew it! wrote:
I suspect you may have a defective 3rd (ground) wire on your electrical circuit. This is a potential safety issue, and needs to be checked out. Know any electricians?
Oh dear. Thanks.
Don't panic here or waste money. The ground wire system is there to protect you in the extreme case where something has gone very wrong and provides a path from the metal of the power supply chassis to ground. So, if you had an short from the hot line to the case it would go to ground through the wire not your body. In normal operation there ground wire is not a factor.
You can easily check this yourself with a cheap simple tester. No need to call in professional help unless this tester reveals a problem.https://www.amazon.co.uk/13-Amp-Plug-So ... B004BLPIBK
And all of the above is likely not related to your problem as you noted neither of the suspect devices has a ground connector.
Is the spark you see a one-time quick event or continuous? If one time and causes a reboot, that seems more like a static discharge. The USB hard drive is isolated via its power supply transformer. So, effectively it is floating ground relative to the computer and gets brought to the same ground potential when you plug in the cable. It could be possible those two grounds are far enough apart that you see a small spark when you initially connect them, but no real current should be flowing.
Just as an aside, I assume you are in the UK based on your currency comment. I was over there this year an noticed several outlets that had switches for the outlet right there on the outlet face. Is that a fairly common arrangement?