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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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PoE Cable Categories
From a PoE perspective we need to remember this:
1.  IEEE 802.3af-2003 assumes a worst-case of AWG26 (CAT3).
2.  IEEE 802.3at-2009 assumes a worst-case of AWG24 for higher-power applications (CAT5e).
(Keep in mind that AWG24 is thicker than AWG26.)
In terms of resistances:
1.  IEEE 802.3af assumes that a 100 m CAT3 cable that has a worst-case (DC) loop resistance of 20 Ω. This is the cable resistance assumed for low-power applications (13 W at the end of the cable).
2.  IEEE 802.3at assumes that a 100 m CAT5e cable that has a worst-case loop resistance of 12.5 Ω (for Type 2 medium power applications). This is the cable resistance assumed for medium-power (Type 2) applications (25.5 W at the end of the cable).
We will ...

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