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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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PoE Is an Intrabuilding Standard
PoE is essentially an intrabuilding standard. There are some confusing references in IEEE 802.3at to Environment A and Environment B:
In Section 33.4.1.1, titled “Electrical isolation environments,” and in Section 33.4.1.1.2:
There are two electrical power distribution environments to be considered that require different electrical isolation properties. They are as follows:
•  Environment A: When a LAN or LAN segment, with all its associated interconnected equipment, is entirely contained within a single low-voltage power distribution system and within a single building.
•  Environment B: When a LAN crosses the boundary between separate power distribution systems or the boundaries of a single building…. ...

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