Here is what happened. I have a Belkin Surge Protector. I have connected my iPhone charger (5v 1A) to this and it powers my Pi. I have also connected powered USB hub, transcend hub3k to this surge protector. I connected my Seagate External HDD to powered USB hub and when I tried to connect the USB to Pi, I suddenly felt the current in Pi. (Pi was already running) Obviously I did not connect and I tried to touch the USB port on cable of hub, I could still feel the current.
I had tested this USB hub earlier and it was working fine. So I reconnected everything this time without surge protector. When I touched the USB port, I felt the current(this time was very less). But after a few seconds, when I touched again, nothing happened. I went ahead and connected this to my Pi. And I touched again on the Pi's USB and I feel no current.
Is it common to feel some current on the powered USB hubs? both usb hub and my HDD are USB 3.0. This is my first time using powered USB hub.
I know that I shouldn't touch and play with electronics, however I just couldn't resist (as I was sure that USB hub was not faulty). I am soon gonna get a multi meter so that I will know.
Now, if I had turned off everything and connected, then I wouldn't have known this problem at all! So, if had done that, could that damage my Pi? So I mostly supplied power to Pi from USB ports, how damaging this could have been?
and also how do I make sure that surge protector here is the culprit?