Re: Ground fault clamp thingummy. Sorry, non-political post.

From: Ken Smith (kensmith_at_green.rahul.net)
Date: 09/18/04 

Date: Sat, 18 Sep 2004 20:57:07 +0000 (UTC)

In article <pan.2004.09.18.20.32.19.695522@bar.net>, Mac <foo@bar.net> wrote:
>On Fri, 17 Sep 2004 16:49:43 +0100, Keith Wootten wrote:
[...]
>So, the equipment has a ground shield, but you want a local ground because
>you don't trust the shield. This part really makes no sense to me. If the
>equipment is designed correctly, why would the shield be faulty?

I've seen the following:

(1) Because the shield has blown open due to an incorrectly applied mains
voltage.

(2) The thing did not get built according to the drawings.

(3) The ground of the outlet it is plugged into is not actually grounded.

(4) The other end of the cable is 4000 feet away and it really is
grounded but due to IR drops this end has +60V on it.

>Besides, how is the local ground more trustworthy than the remote one? Is
>it bare cable, bolted directly to a spike hammered into the Earth right
>at the test bench?

Usually (where I work), all of the outlets have a "ground" pin and all of
the metal of the bench and the grounds of the equipment are all connected
to it. It really doesn't matter if it is ground or +500V so long as all
voltages are referenced to it. If someone brings a real ground connection
into the picture it really starts to matter. 

-- 
--
kensmith@rahul.net   forging knowledge

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