USB Port Sparks

Phone the supplier you bought it from with the intention of taking it back and having it tested. It sounds like you are still under guarantee (and I hope you bought Applecare). Anything electrical that sparks is not good news in my opinion.

Your iMac has a grounded aluminum enclosure tied directly to the grounding pin on your electrical outlet. Unless you have a miswired electrical system in your house then I doubt that your iMac is the cause of the arching. I suspect that it is the USB peripheral device you are plugging into the iMac that is providing the voltage that causes the arching.

If you have a multimeter you could measure the voltage between the iMac enclosure (aka ground) and the USB cable housing to see if there is a measurable voltage coming from the USB peripherals. The metal USB connector housing is the most likely culprit because it's the part that makes contact with the iMac enclosure first when you are connecting it. If in doubt you could have an electrician test your wiring. Be sure to note that the iMac enclosure appears to have a finish that may not provide a good electrical connection when trying to take a voltage measurement. You may need to find an area where the finish is scratched down to bare aluminum, or just use the electrical ground from the outlet. If you don't know how to do this safely then bring in somebody who does.

At my house I use one of the inexpensive circuit testers like the one linked to below to verify that my outlets are wired correctly (ground/hot/neutral). I actually found a couple of outlets that had been mis-wired (hot and neutral reversed).

3-wire Circuit Tester

USB arching usually isn't a problem.

I suggest powering down your USB devices, then plugging them into your iMac. There shouldn't be any sparking. If there is, then you have static electricity issue. Once plugged in, power them up and you should be fine.

What devices do you have plugged into the iMac?

icare is obviously knowledgeable about electricity and the advice seems sound to me ... but. You can never be too sure. If I buy a piece of electrical equipment and I find myself beset by sparking ... I want to know it is safe. And the people to assure me are those that sold the item to me.

Get it professionally checked out ... you only have one life.

Hi,

I had a similar sparking issue both with a DLink USB powered hub plugged into a Mac Air, and a Samsung powered hub plugged into an HP laptop, so its not Mac-specific.

Its cause the hub wasnt earthed, and some voltages leaked onto the USB plug's sheath. To diagnose that it is in fact the issue, check:

* Does the sparking occur when the hub is unplugged from power?

* Does it happen when the laptop runs on battery? (unplug from mains, not just switch off mains)

In my case, both devices had to be powered to see the sparks.

To fix it, I fashioned an earth by taking another usb cable, plugged it into an unused port on the hub, cut up the other end and connected the sheath within to earth (note that some cheaper USB cables have only 4 wires and no sheath).

Cons: Cost of 1 USB cable, and i lose one port on my hub.

Pros: Potentially better life for my machines. I did notice that whenever the sparks occurred, the mac would briefly shift to battery, hence i realized that the flow of electricity may not be a trivial matter.

Cheers!