🚀 go-pugleaf

USB only uses 4 wires for each USB port.  Motherboards usually have two
USB ports in a 5x2 pin block.  Some have a pin missing on the
motherboard and this is I suppose a keying pin to keep the connector on
only one way.  Like mouse connectors on motherboards, Com ports (16th is
not used).

So my guess it is a keying pin.  Some manufactures don't bother with
keying pins and modified connectors as they cost more, they expect you
to line up pin 1 and the cable with the striped wire correctly.

And a lot of connectors have dual grounds, look at audio cables for
CD-ROM to sound cards.  There are four wires Right Ground Ground Left. 
Only more expensive sound cards have a cable using that pattern.  You
are supposed to shield each channel individually.  Instead they cheap
out and shield both channel wires with a common shield leaving a ground
connection free.

I would assume USB cables are being made without the ground shielding
leaving that ground pin on the connector free.

So a keying pin and or shield ground would be my guess.

Fred Klabuster wrote:
> 
> Does anyone know why the USB port has two ground / neutral / mass cables
> on the board side (i. e. on the other side of where you plug your
> equipment in)?  I have an Epox mainboard, BAT sized, and just bought the
> USB connector thingie for it.  What I noticed is this:  the USB port has
> FOUR visible sprockets, the USB-socket-to-mainboard cable has FIVE
> wires, and the mainboard has FOUR sprockets.  When I took it back to the
> shop, the salesperson told me that the fourth and fifth wire were both
> DC - ground, so that the fifth wire "wasn't really needed".  I find that
> a bit hard to believe.  Can anyone tell me what this fifth wire IS and
> what it DOES?
> Please e.mail me as well as replying to the group.  MANY thanks in
> advance.

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