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
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
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.
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From: Geoff Thompson [mailto:gthompso@xxxxxxxxxxxxxxxxxx]
Sent: Monday, January 13, 2003 6:48 AM
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.
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 |
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