grounding questions...

[René Schmitz]

At 18:53 13.05.00 +0200, you wrote:
>René Schmitz wrote:
>> At 15:25 10.05.00 +0200, Ingo Debus wrote:
>> >What about the tip of a phone jack (when the other end of the cable is
>> >plugged into a mains powered unit)?
>> >
>> >;-)
>> 
>> In essence this is connected to ground via the output of the circuit.
>> I think there needs only be a conductive path to mains GND
>
>This is no 'direct' connection, there are electronic parts in between.
>If there's an accidental connection between the live line and some point
>in the circuit no-one can guarantee that these parts are fried before
>the circuit breaker trips.

In the case of failure in a device whose chassis is connected to GND,
nothing ensures as well that you don't get fried touching the case until
the circuit 
breaker trips! (Or the fault current interruptor if there is one!)

I believe to recall that a device which doesn't have double insulated PSU 
musn't have any external connections (exept where these are not
galvanically coupled)! 
The point would be that we must use double insulated transformers/PSUs anyway.
The GND connection is merely an extra. And then its safe for the tip not to
be grounded. 

But as Tony already pointed out: classification of our homebrew devices is
difficult, I guess most falls inbetween class 1 and 2 with a questionable
safety.

Bye,
 René

-- 
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