As a follow-up to my previous posts in this thread, I came across this
doument from Cisco on Earthing and Bonding Recommendations for their MGX8800
routers. It is consistant with "grounding" schemes I had worked on, and many
other telco equipment providers.
Since pictures are worth a thousand words look at Figure C-2 to see the
number of "gnds" there are, but ultimately they are all one node just
labeled differently at different points.
http://www.cisco.com/c/en/us/td/docs/switches/wan/mgx/hardware/mgx8800_serie
s/installation/guide/hig/8850_apC.html
Hope this clears confusion,
Bert Simonovich
Signal/Power Integrity Practitioner | Backplane Specialist | Founder
LAMSIM Enterprises Inc.
Web Site: http://lamsimenterprises.com
Blog: http://blog.lamsimenterprises.com/
________________________________
From: Boris Bakshan [mailto:bbakshan@xxxxxxxxx] ;
Sent: 7-Jan-17 2:40 PM
To: bertsimonovich@xxxxxxxxxx
Cc: Lee Ritchey; si-list
Subject: Re: [SI-LIST] Re: An Article on what ground is
Bert,
Sorry, I'm not following... You previously mentioned that only one GND
exists in a system. Is there any connection between this GND and Chassis
GND?
Lee - by "card cage" do you mean the chassis itself?
On Sat, Jan 7, 2017 at 9:30 PM, Bert Simonovich <bertsimonovich@xxxxxxxxxx>
wrote:
Boris,
It isn't any different. The actual "Chassis Gnd" of the shelf is
connected to the frame or rack which is connected to the IBN of CBN of the
facility which is effectivly "earth gnd".
________________________________
From: Boris Bakshan [mailto:bbakshan@xxxxxxxxx] ;
Sent: 7-Jan-17 2:03 PM
To: bertsimonovich@xxxxxxxxxx
Cc: Lee Ritchey; si-list
Subject: Re: [SI-LIST] Re: An Article on what ground is
Hi Bert, Lee,
This makes completely sense.
However, as with any commercial electronic device that has a
metallic enclosure (VCR, amplifiers, multimedia boxes, etc') connected to
Earth/Safety ground via third contact in a power cord, I would expect the
same thing with a Shelf/Chassis. Why should this be different ? For safety
reasons, why shouldn't the (conductive) body of any chassis be connected to
earth ground?
Thanks.
On Sat, Jan 7, 2017 at 8:54 PM, Bert Simonovich
<bertsimonovich@xxxxxxxxxx> wrote:
Boris,
I have done essentially the same thing Lee has described in
all of the
backplanes I have designed in the past, except that in our
case the outer
PCB layers on both sides were "GND" plane, and the PCB was
edge plated. This
created a faraday shield for all the internal layers. The
backplane was
metalically connected to the shelf framework with screws
without isolation.
There was only one "GND" in the system, including the line
cards that
plugged into the shelves.
This "grounding" scheme was compatible with single-point
ground/integrated
bonding network (SPG/IBN) and mesh/common bonding
network(Mesh/CBN). Our
systems had to meet GR-1089-CORE - Electromagnetic
compatibility and
electrical safety for network telecommunications equipment.
-48V Battery and Battery return powering the system was
isolated from the
"Chassis GND" with an option to join the battery return to
"chassis ground"
at the single power entry point.
Regards,
Bert Simonovich
Signal/Power Integrity Practitioner | Backplane Specialist |
Founder
LAMSIM Enterprises Inc.
Web Site: http://lamsimenterprises.com
Blog: http://blog.lamsimenterprises.com/
<http://blog.lamsimenterprises.com/>
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx ;<mailto:si-list-bounce@xxxxxxxxxxxxx> ]
On
Behalf Of Boris Bakshan
Sent: 7-Jan-17 1:16 PM
To: Lee Ritchey
Cc: si-list
Subject: [SI-LIST] Re: An Article on what ground is
Hi Lee,
Thank you for prompt reply.
So, in fact, you are making a direct connection between the
logic ground of
the cards and the metalic chassis enclosure so that
backplane ground (return
path of signals) , cards logic ground and metalic chassis
enclosure are all
connected, did I get it right?
On Jan 7, 2017 7:57 PM, "Lee Ritchey"
<leeritchey@xxxxxxxxxxxxx> wrote:
> Thanks for the nice feedback.
>
> Aha! You have asked an EMI question! I use the ground
plane in a
> backplane as one side of my Faraday cage. Where that
backplane meets
> the flanges on the card cage, I leave the copper on the
top layer and
> connect that with vias to the ground plane in the
backplane. Now,
> there is the one connection between logic ground and the
Faraday cage.
> There can be no other connections such as on face places
if one is to
> avoid "leaking" at the cracks which is a common complaint
when more
> than one connection is made between logic ground and the
Faraday cage.
> Notice, I did not use the phrase "chassis ground" in this
discussion.
>
> I have used this method in dozens of systems with very
good EMI results.
>
> Hope this helps.
>
> Lee
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx
<mailto:si-list-bounce@xxxxxxxxxxxxx> ]
> On
> Behalf Of Boris Bakshan
> Sent: Saturday, January 7, 2017 5:24 AM
> To: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
> Cc: si-list <si-list@xxxxxxxxxxxxx>
> Subject: [SI-LIST] Re: An Article on what ground is
>
> Hi Lee,
> Very good, comprehensive article, thank you.
> What is your recommendation when it comes to backplanes? a
backplane
> is attached to the chassis with bolts/other conductive
mechanical
> parts. Do you recommend plating these PCB holes in the
backplane? If
> you do, should these holes be connected to (any)
electrical net?
>
> Thanks Lee.
>
>
> On Fri, Jan 6, 2017 at 10:43 PM, Lee Ritchey
> <leeritchey@xxxxxxxxxxxxx>
> wrote:
>
> > I have written an article on ground following the brisk
exchange on
> > this subject last month. I hope it clears up some of
the confusion
> > around this subject.
> >
> >
> > Here is where it is on the web.
> >
> >
> >
> > http://ubm.io/2ikEDat
> >
> >
> >
> > Lee Ritchey
> >
> > Speeding Edge
> >
> > P.O. Box 2194
> >
> > Glen Ellen, CA
> >
> > 95442
> >
> > 707-568-3983
> >
> >
> >
> > I just used the energy it takes
> >
> > To get mad and wrote some blues.
> >
> > Count Basie
> >
> >
> >
> > Or:
> >
> > Worry is like a rocking chair,
> >
> > It keeps you busy but.
> >
> > It doesn't get you anywhere.
> >
> >
> >
> >
> >
> >
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