Hans....
I may be wrong in my explanation to the following question you posed but I
will give it a shot.....You said:
I don't know any reason why the system has
to be keyed, I always assumed the US development of keyed plugs
was triggered by old DC systems (since in DC Eq. it is necersarry
to know the orientation), but not a new addition. Strange, we
dropped all orientationwhen switching to AC (with Protective
Ground). Could anyone give give a reason why the system has
to be keyed _IF_ a Protective Ground is included (other than
define the Protective Ground pin)
If you hook an scope up circuit such as a TV and hook the ground probe up to
signal ground but you have the plug reversed the circuit will short out and
you will blow the device you are testing. That is because you just provided
a current path to frame ground for the signal which you thought was signal
ground. TV repairman who have used scopes have done this more than once.
Tony Niemann
2606 Merriwood Avenue
Louisville Kentucky 40299
tniemann_at_msn.com
502-267-9233
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Received on Tue Oct 02 2001 - 05:27:56 BST