From: Robert Baer
X-Mailer: Mozilla 4.75 [en] (Win98; U)
Subject: Re: what is this chassi symbol in the pic for?
Date: Sun, 08 Sep 2002 08:07:48 GMT
NNTP-Posting-Date: Sun, 08 Sep 2002 01:07:48 PDT
Organization: EarthLink Inc. -- http://www.EarthLink.net
David Jones wrote:
> I don't understand what the chassi symbol at the bottom of the schematic,
> which is in the file attachment of this post, means. if there are several
> of these chassi symbols, which i've seen before, what does that mean? are
> they all connected? when does electricity flow in that direction?
This is not common; either a ground symbol is used, or no ground is
shown (not common).
The chassis symbol (which was shown) is nominally reserved to show
components that are directly connected to a metal chassis, which may or
may not be a common wire for all of the circuitry.
The ground symbol is normally used as a common wire for all of the
In either case, current going into this "wire" from one or more
component will flow out to one or more other components; the net is
zero, just like any other wire.
There has been a lot of equipment that used a common wire for ground,
which was completely insulated from the metal chassis.
And in some of those, i have seen two capacitors of equal value, each
one going from one side of the incoming 2-wire power cord to the
chassis. That configuration was supposed to be a safety feature, and it
is obviously poor engineering and potentially very dangerous.
In some other cases, only the power transformer core is connected to
the chassis, which is connected to the third wire (ground).
In yet other cases, only the ground lead of the circuitry is connected
to the case (chassis) at one point, which is connected to the third wire
(PC computers are an example).
So one could show this in a schematic with a line from one ground
symbol to the other.