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Hi all,
There are some potential issues that we need to check before we take the option of allowing 3 pair with high back feed voltage I.e requiring to meet back feed only for 2-pairs.
A) some PSEs are implemented with current source and a resistor across the PI to generate the detection voltage. This resistor was used to see just up to 30v . Now it will see 57v for ever. This is power dissipation issue I.e. Potential
damage to legacy 4-pair equipment. Rack bent or need to check if he Ok with it.
B) what will happen when PSE will be connected through crossed cable over 2pair and now 57v will be with opposite polarity on the in unpowered pair which will destroy the diode across the PSE PI or the Ideal diode bridge at the
PD.
C) When Midspan and Switch are connected together over 2-pair each with crossed cable, a potential of >60v may happen.
All the above worries are for the use case of a 4-pair PSEs operating over 2-pair.
I planned to verify it before the meeting however, columns make it, and also can't attend the meeting today. So please check these issues if they are real.
Yair
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