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[802.3af] ground one side?

Good notes, Yair! Yes, you guys talked us out of doing this, about two years ago.

Still, lots of people will do it. 

And, the battery plant is "positive ground." ;-) Lucas notwithstanding:



-----Original Message-----
From: Yair Darshan [ YairD@xxxxxxxxxxxxxx]
Sent: Monday, January 13, 2003 5:15 AM
To: 'Geoff Thompson'; stds-802-3-pwrviamdi@xxxxxxxx
Cc: thompson@xxxxxxxx
Subject: RE: [802.3af] Late comment

Geoff and all,

The reason that there is no specification for tying one of the PSE outputs
to the ground is the fact that in the early days of the standard (802.3af)we
got the conclusion that it is best to leave the outputs floating!.

It was once offered by Steve Jackson/Jennifer Rasimas/Nortel on July 10,

to tie one of the leads to the ground however it was voted down from the
following reasons:

1. In environment A, when single power supply is used to feed multiple
ports, the effective way to avoid
current ground loops is by keeping the PSE port floating or DC
isolated from system/chassis ground along with the PDs.

2. If you tie one of the PSE outputs to ground, it means that you tie
the MDI leads to ground.
This connection violates IEEE802.3 specific requirement which
specify 1500Vac or 2250Vdc between all MDI leads to frame ground/chassis and
repeater circuits.

3. If you tie one of the PSE outputs to ground, it means that the port
is no longer ac balanced and it may affect the RF parameters.

4. In any case if eventually we will find good reasons why we should
tie one of the PSE outputs to the ground than it must be the positive 
lead as it is being done for 100 years or so in the telecom field
however in the telecom infrastructure we didn't had the RF issues and
the IEEE802.3 requirements to consider..

From the above reasons I do not agree to change the standard as offered by

If any one think differently please lets discuss it over the reflector and
not at the meeting in order to save the time.



Darshan Yair
Chief Engineer
PowerDsine Ltd. - Powering Converged Networks
1 Hanagar St., P.O. Box 7220
Neve Ne'eman Industrial Zone
Hod Hasharon 45421, Israel
Tel: +972-9-775-5100, Cell: +972-54-893019
Fax: +972-9-775-5111

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-----Original Message-----
From: Geoff Thompson [ gthompso@xxxxxxxxxxxxxxxxxx]
Sent: Monday, January 13, 2003 6:48 AM
To: stds-802-3-pwrviamdi@xxxxxxxx
Cc: thompson@xxxxxxxx
Subject: [802.3af] Late comment


During the meeting in Vancouver I asked the group's indulgence with respect 
to acceptance of yet another comment from me.

There seemed to be general agreement that the comment addressed an issue 
that was important enough that it should be accepted.

The comment:
I can find no place where there is a specification as to which side of PSI 
is tied to ground (i.e. negative ground vs. the positive ground usually 
found in mid-fifties British sports cars with Lucas electrics.) I request 
that a specification be added that dictates which side of the supply is 

This documents my request to add this comment to the database and address 
it during the Santa Clara/January meeting.



| Geoffrey O. Thompson |
| Vice Chair, IEEE 802 |
| Nortel Networks, Inc. M/S: P79/06/B04 |
| 4655 Great America Parkway |
| P. O. Box 58185 |
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| Phone: +1 408 495 1339 |
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