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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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Safety in AC Disconnect
There is one requirement that the standard stipulates, but it is widely overlooked and not tested for either: The amplitude of the AC-probe signal. Though that is not directly specified, the standard does say that if the PD is suddenly disconnected, the port voltage (incoming DC with the open-circuited AC superimposed) should never exceed 60 V. The problem with PSEs that use a 5-V probe amplitude is that if the port voltage is at its maximum-DC level of 57 V, adding the 5 V on top of that takes it to 62 V, which exceeds the safety threshold of 60 V. Therefore, any solution, which targets a nominal AC-amplitude of only 2.5 V, with a max of 3 V is compliant, others are strictly not. Though no one may ever know!
One key ...

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