USB on iMac Sparking?

[PeterHsieh]

Hey MacTalk'ers

Just wondering if anyone with a iMac (in particular a 27" one) has seen sparking around USB port area around the iMac.

I was plugging in a USB cord when the metal (of the USB head) came in touch with the side casing of the port, and I could see tiny little sparks. (and when i say tiny.. they look like little dots of light)

I was stupid enough to go touch it.. with my finger.. not getting electrocuted, so i presume its a very small current running through....

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Ok... just found out its caused by the power running through the USB cord, (as it is attached to a HDD dock with has external power connected to it....)

I guess this is just a head up type of thing ...

Peace Out!

[milliedog]

Two comments on this one. Firstly, you are right about the power. School kids have been known to use a paper clip or coin to short out the USB port - "Oh wow, it sparks!"

Secondly, I've never had it happen to me with USB, but I have felt a sting from groping around the back of hard drive while connecting a firewire cable - so watch what you are doing!

[iPirate]

I think FireWire's 12V. I used a FW-powered fan on the back of my MBP for a while when I was worried about it heating up too much with long Handbrake encodes.

[thre3dee]

Hmm. USB is only 5 voltz right? 5V is nowhere near enough to cause even a remotely large spark (you need about 3000V for 1mm spark), so something is probably not quite right.

[joshm]

I have the same issue with my G4 Powerbook that's acting as a server. Plugging in USB cables often spark. This is NOT GOOD™, but I've not figured out what causes it.

[soulman]

Hmm. USB is only 5 voltz right? 5V is nowhere near enough to cause even a remotely large spark (you need about 3000V for 1mm spark), so something is probably not quite right.

What you're thinking of there is an arc. Sparks occur most easily with DC, which is one of the reasons mains power is AC, and they require current flow, but they will happen even at low voltages. If you connect or disconnect something that is drawing power or trying to do so, you will most likely get a spark.