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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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Failing the Hi-Pot Test
We can fail the hi-pot test for any number of reasons. With special attention to PoE, some of these reasons are
1.  Capacitors bridging the two domains may have inadequate ratings. In PoE these caps are the Y-caps from PoE/MDI side to the enclosure/host. They should be 2.5 kV, but most vendors use 2 kV.
2.  We also showed in Chap. 9 that the 10- or 22-nF blocking caps in the terminations can fail because of the voltage distribution.
3.  The same could happen with the port capacitors, especially if they are very small. We can calculate how much voltage will directly fall across the port capacitors (both the PD and PSE sides) with 2500-V applied hi-pot voltage.
4.  The data/pulse transformers can be substandard. We ...

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