[GreenKeys] Grounding and GFI's

[Roy Morgan]

At 01:45 PM 2/13/2005, Buzz wrote:

>Then there's the problem of a grounded neutral.
>http://www.softcom.net/users/buzz/temp/Linenoise.html


Buzz,

I assume that by "...the problem turned out to be the 120V AC common lead 
shorted to ground. " you mean that the neutral wire (white) was shorted to 
the rack cabinet frame (which was connected to the safety ground (bare or 
green) wire.

The current in the neutral wire back to the distribution panel causes a 
voltage between the neutral and the ground at the equipment. But 
your  waveform looks odd, so there the situation is likely more complicated 
than this.

Thanks for your info.. It may well help others solve a pesky noise 
problem.  Great use of a scope!

Roy





>the problem turned out to be the 120V AC common lead shorted to ground.



>Buzz
>
>
>On Sun, 13 Feb 2005 10:37:49 -0500, you wrote:
> >Hi
> >
> >GFI's are a significant problem when it comes to older gear. Since they
> >trip out on minor current imbalances they are really designed to work
> >with gear that has total isolation of the AC line to ground. The other
> >thing that they depend on is a single path back to ground *through* the
> >GFI. It's this second requirement that often gets messed up. Cross
> >grounding gear between different GFI'd circuits is a no-no. Running a
> >grounded antenna to the chassis of a GFI'd radio is also against the
> >rules. If the Model 28 is on one GFI and the computer is on another GFI
> >that's a problem if there is a direct ground connection between the
> >28's keyboard and the frame ground on the RS-232 input on the computer.
>
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- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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