[sdiy] semi-OT: USB cable shield

[Colin f]

At a guess, assuming the outer shield makes contact first, the high
resistance would limit the sudden current flow between ground isolated
devices that might be floating at very different DC voltages.
Once the ground pin connects, you get the low resitance connection you need.

Cheers,
Colin f

> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl 
> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Ingo Debus
> Sent: 22 April 2014 20:13
> To: synthdiy diy
> Subject: [sdiy] semi-OT: USB cable shield
> 
> Hi all,
> 
> as far as I know, the shield of USB connectors usually is 
> connected directly to ground. However I've seen designs where 
> there's a smallish capacitor (10 nF) in parallel with an 1 
> megohm resistor between the housing of the USB receptacle and 
> ground. Why is this? I understand this is done for MIDI 
> connectors to break up ground loops (see? it's not completely 
> OT), same for Ethernet, but USB? USB connectors have a ground 
> pin anyway, so it seems pointless to me to break the ground 
> shield connection for low frequencies while there's still a 
> direct ground connection via the pin.
> 
> Any Ideas?
> 
> Ingo
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