Power leak - aluminium enclosure

I just bought a WD 3TB My book Studio external drive - firewire with aluminium enclosure. I had a usb cable plugged into my computer and I noticed a spark from the plug as it touched the hard drives aluminium enclosure. I thought that’s wrong. Was I imagining things? I certainly was not going to try that again. Then a bit later I brushed my arm against the drive and I noticed a distinct tingle as the drive shocked my arm. This only happened when my other hand was earthed to the metal case of my iMac. So getting a bit concerned by this time, I took a look at the back of the drive. What I saw was a design fault where the aluminium enclosure actually touches the power plug. There is only a small clearance and alignment is out. What I then did was wrap some sticky tape around the base of the power pin to insulate it from the aluminium enclosure and this solved the problem. I will most likely return the drive. But what I was wondering if anyone has heard of this problem before and is there much of a risk of frying my computer or other components due to the leak. Like the usb plug with the metal outer casing picking up the current? Any ideas - thanks?

Haven’t seen that problem before, maybe a defective power plug. You can also try connecting the power cable to another power socket to see if that helps. But if you notice that the problem continues, you can create the RMA online. 


If you plug the USB cable into the enclosure and leave it disconnected from your computer, do you feel a tingle when you touch the exposed connector? If so, then your enclosure’s ground reference point is rising to the voltage level of the AC adapter’s negative DC terminal. This voltage is usually half the mains potential, ie 60VAC or 120VAC, depending on your locale. Although it sounds dangerous, it is in fact harmless (to you) because it is coupled via a high impedance Y2 capacitor.

Similar problems occur in other domestic appliances that are fitted with a 2-prong AC plug. For example, here is the power supply section of a DVD recorder:


Notice the blue disc-shaped ceramic capacitor to the left of the “MSC” transformer and above the 68uF 450W bulk capacitor. It straddles a hot-cold demarcation line and connects the AC side of the supply to the DC side. That’s what gives you the tingle. The capacitor will have a Y2 safety rating that guarantees that it can never fail in a short circuited mode.