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Re: [8023-POEP] What's the max voltage drop thru a midspan?



Hi Steve,

Do you think the following text contained in the third from last paragraph 
of subclause 33.4.8 'Midspan PSE device additional requirements' of IEEE 
Std 802.3-2005 covers what you are looking for:

---oo000oo---

Configurations with the Midspan PSE in the cabling channel shall not alter 
the transmission requirements of the "permanent link." A Midspan PSE 
inserted into a channel shall provide continuity for the signal pairs. A 
Midspan PSE shall not provide DC continuity between the two sides of the 
segment for the pairs that inject power.

---oo000oo---

Regardless, I agree that the IEEE 802.3at specification will need to be 
written carefully to ensure that, for example, it doesn't retrospectively 
place a higher current carrying requirements on existing IEEE Std 
802.3-2005 compliant Mid-Span PSEs.

Regards,
  David



owner-stds-802-3-poep@xxxxxxxx wrote on 10/06/2006 05:34:39:

> Guys,

> 
> As you all know, we're planning to run current from the endspan thru the
> midspan in a 4P system.

> 
> Although I think its unlikely that we'll see Af-midspans with fused 
traces
> or delaminated boards, technically we can't prove that it won't happen
> because 802.3af doesn't specify a min current rating for this path. 
There
> seems to be no max limit for dc resistance either.  (If these specs are 
in
> 802.3af and I've missed them, then someone please point me to the 
applicable
> table or paragraph.)

> 
> We should make sure 802.3at specifies both these parameters.  (But only 
for
> midspans that output >15.4W so we're not retroactively putting new
> requirements on Af-midspans.)

> 
> Any comments?

> 
> Steve

> 
> [attachment "C.htm" deleted by David Law/GB/3Com]