Xref: utzoo unix-pc.general:6309 comp.sys.att:10653
Path: utzoo!utgpu!watserv1!watmath!uunet!shelby!apple!voder!pyramid!ctnews!mitisft!dold
From: dold@mitisft.Convergent.COM (Clarence Dold)
Newsgroups: unix-pc.general,comp.sys.att
Subject: Re: UPS/SPS testing re: AC protective ground
Message-ID: <1643@mitisft.Convergent.COM>
Date: 23 Oct 90 15:04:33 GMT
References: <35147@cup.portal.com>
Organization: Convergent Technologies, San Jose, CA
Lines: 23

in article <35147@cup.portal.com>, thad@cup.portal.com (Thad P Floryan) says:

> My systems are properly grounded at ALL TIMES, all my RS-232 connections have
> pin 1 connected straight through, and my hands are NOT charred stumps.  :-)

On other Convergent Systems designed in the 3B1 era, pin 1 was not a good
place to attach the drain from the shield on an RS232 cable.

The chassis and logic ground are separate, "stitched" together with a number
of capacitors.  All of that shielding metal is to keep the zaps on the
outside.

Tying the shield to pin 1 allows the zaps to sneak inside, even if only for
an inch or two before they go to chassis ground (separate from logic ground).

Much better to tie the shield to the metal body of the connector, which must
always be secured to the chassis with screws.  Some connectors have a separate
tabe for attaching the shield.  Otherwise, it must be tack-soldered.
-- 
---
Clarence A Dold - dold@tsmiti.Convergent.COM            (408) 435-5293
               ...pyramid!ctnews!tsmiti!dold        FAX (408) 435-3105
               P.O.Box 6685, San Jose, CA 95150-6685         MS#10-007