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RE: [802.3af] < 60v

Hi Roger,

There is no doubt that 60V is max under all operating modes..
It is not clear to me why you thought that I spec differently.
If you refer to the sentence "PSE port output voltage shall not exceed 60V
during disconnect detection phase" as
stated in "Disconnect detection ad hoc meeting March 2002.ppt" or in
"Meeting to get consensus, March 12.ppt" files than it is part of the
specification of the disconnect detection black-box parameters. The reason
that we specify this explicitly here is due to the special case that we add
additional ac voltage source above the dc level which may heat the 60V line.
Therefore, to prevent miss understanding we specify this requirement.
In the draft you may find the requirement that the PSE output is spec to be
an SELV grade which implies the following:
-Max voltage is 60Vp or DC.
-The voltage may be higher than 60V and less than 120V if it last less than
200ms on non repetitive base. 
 (See UL1950, EN60950 safety standards)

It is not imply that the 57V should move down and the reasons for it are:

Case 1:
Assuming that the ac voltage when PD is not connected will be 5Vpp max for
more than 200ms, it means that the PSE designer need to use 52Vdc max power
source. If he use 3Vpp than the DC source should be 57-3=54Vdc

Case 2:
Assuming that the ac voltage when PD is not connected will be 5Vpp max for
less than 200ms, it means that the PSE designer can use 57Vdc source in
addition to the 5Vpp source (all together 62V) which is OK according to SELV
definitions if it last for less than 200ms. (on non repetitive base which I
don't remember the definitions for that in terms of max duty cycle..)

Case 3: 

If you use the DC disconnect method that there is no imposed ac voltage so
the 57V max still holds.

The bottom line is that:
- we need to keep 60Vp or DC max to keep SELV definitions.
- We need to keep 57Vdc max PSE operating voltage including the effect of
the additional ac signal.
  Please note that 57Vdc+(5Vpp with duty cycle of 50%) can be 57Vdc as

If you believe that we should use different wording to make this clearer
please compose one and lets discuss it.
The target is not to change old IEEE802.3af numbers. Lets keep it simple.



-----Original Message-----
From: R karam [mailto:rkaram@xxxxxxxxx]
Sent: Tuesday, March 19, 2002 9:30 PM
To: stds-802-3-pwrviamdi@xxxxxxxx
Subject: [802.3af] < 60v

Hi Yair

fyi, we should not exceed 60v under any conditions... please
keep this in mind as you spec this, my first find.
if this means that the 57v has to move down, we would need to
bless this with avaya....