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Calculating the total power needed

There are currently two standards for PoE: 802.3af allows for a maximum of 15.4 W per channel, whereas PoE 802.3at doubles the available power to 25 W.

To ensure that sufficient power is available per switch, you need to calculate the total power consumption requirements for all equipment that will be connected to a specific switch on a network. This total wattage requirement must be less than the switch’s PoE power budget – total PoE power per switch and per port.

Figure 7 describes minimum and maximum power consumption levels required for both the Power Sourcing Equipment (PSE) and the Powered Device (PD).

Determining the appropriate PoE

The PoE powering of a device becomes more critical depending on temperature. Many devices can function at different low temperature levels based on the amount of power available. It is imperative to verify that the correct midspan is used for exterior cameras. As seen in Figure 8, when high PoE is used, the AXIS P1344-E can operate at temperatures down to -40°C.