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I would
not design a system with long cables without some form of voltage clamping
device(s). You are asking for trouble. Simple Trans-sorbs, high power
zener clamps, is the solution here. Mov's might work but degrade with
use.
Ed Walker
Technical Staff
Analog Product Specialist
Texas Instruments
Incorporated
HC66 Box
203
Mountainair, NM
87036
INTERNET: ed_walker@xxxxxx
WEB SITE: http://www.ti.com
Office
= 505-847-0576
Robert,
The reason for the
discharge path is the IP Phone which may have only a LAN connection.
In the
telephony domain, one purpose of the discharge path is to slowly discharge a
user that contacts the phone.
When I did a rotational assignment at
Indianapolis in the mid 60's, they had an interesting story concerning the first
colored phone.
The color plastic unlike the black plastic was an excellent
insulator. Due to the cost premium, users were executive with carpeted
offices. These users often had accumulated a large charge which was
discharged when the user talked into the transmitter in the hand set.
Black phone users were discharged by the poor insulating plastic.
Dieter
RDLove wrote:
OK, we got email notes from two of the experts
(Larry and Roger) indicating this is not a real issue. Unless there is
strong objection, I will take it off the issues list. If there is strong
disagreement (and this process will be in effect for any potential issues
raised) then it will stay on the list until the task force resolves
it. Best regards, Robert D. Love
President, LAN
Connect Consultants
7105 Leveret Circle
Raleigh, NC 27615
Phone:
919 848-6773
Fax: 720 222-0900
email: rdlove@xxxxxxxx
----- Original Message -----
Sent: Friday, September 15, 2000 4:21
PM
Subject: RE: Static
Discharge I
wasn't raising an issue, Bob.
Dieter was just asking
how Ethernet avoided the Telco grounding, and I was explaining "what it is".
At least, that's what I intended.
Roger seemed to think
I was taking a position of some sort. Look at Dieter's post, then
mine.
Cheers,
Larry
-----Original
Message-----
From: RDLove [SMTP:rdlove@xxxxxxxxx]
Sent:
Friday, September 15, 2000 12:09
PM
To: 802.3af
Subject:
Fw: Static Discharge
I meant to send the attached to all
802.3af. Sorry for the duplicate email to you, Larry.
Best regards,
Robert D. Love
President,
LAN Connect Consultants
7105 Leveret
Circle
Raleigh, NC 27615
Phone: 919 848-6773
Fax: 720
222-0900
email: rdlove@xxxxxxxx <mailto:rdlove@xxxxxxxx>
----- Original Message -----
From: RDLove
<mailto:rdlove@xxxxxxxxx>
To: Larry Miller <mailto:ldmiller@xxxxxxxxxxxxxxxxxx>
Sent: Friday, September 15, 2000 3:07
PM
Subject: Re: Static Discharge
Larry, thanks for your input. I
agree with all you say, but still don't know if this is an issue that
needs to be addressed. I would like to hear from other experts on
it.
Best regards,
Robert D. Love
President,
LAN Connect Consultants
7105 Leveret
Circle
Raleigh, NC 27615
Phone: 919 848-6773
Fax: 720
222-0900
email: rdlove@xxxxxxxx <mailto:rdlove@xxxxxxxx>
----- Original Message -----
From: Larry Miller <mailto:ldmiller@xxxxxxxxxxxxxxxxxx>
To: Dieter Knollman <mailto:djhk@xxxxxxxxxx> ; stds-802-3-pwrviamdi@xxxxxxxx <mailto:stds-802-3-pwrviamdi@xxxxxxxx>
Sent: Friday, September 15, 2000 1:07
PM
Subject: RE: Static
Discharge
Ethernet stuff is
not intended to run outdoors like regular telephones. The biggest risk
these days is picking up static electricity when the cables are pulled
through conduits and wiring troughs. That seems to get worse the better
the cabling gets (cat5E and up) due to
triboelectricity.
The insulation
scheme was chosen to accommodate ground level shifts within building
premises wiring (different AC feeds to different boxes). The wiring
cables float (up to 2250 VDC) with respect to ALL of these. There has
been much discussion in the 802.3af work group on how to handle
DC-powered cables. The 802.3 standard defines two environments ("A" and
"B") with respect to port-to-port isolation (See 802.3 spec or some of
the 802.3af presentations on the IEEE public site).
You are supposed
to used fiber optic links if you exit a building. IP phones are supposed
to be within a building, with the only wiring going to an Ethernet hub.
Wall warts if used are double insulated.
The 2kV caps are
not supposed to be leaky.
Larry
Miller
-----Original Message-----
From: Dieter Knollman [SMTP:djhk@xxxxxxxxxx]
Sent: Friday, September 15, 2000 9:53 AM
To: stds-802-3-pwrviamdi@xxxxxxxx
Subject:
Static Discharge
Hi,
My background is telephony. I'm totally new to 802.3, so
please excuse
my
ignorance.
One thing
that appears strange is the lack of an intentional
discharge
path for the
potential on the cable.
The only means that I have found is breakdown of the common
mode
termination
capacitors.
Are these
caps with 2 kV rating intended to be leaky?
On POTS line interfaces the Tip lead is typically biased around
ground
and serves as a
discharge path to earth ground for Analog Sets. Do
the
IP Phones require a
discharge path via the LAN?
Dieter Knollman
DMTS
Lucent
djhk@xxxxxxxxxx
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