Site survey considerations

Power over Ethernet (PoE)

There are currently two standards available for PoE:

  • 802.3af provides a maximum of 15.4 W per channel
  • 802.3at provides up to 30 W per channel

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

Table 1 describes the minimum and maximum power consumption levels required for both the Power Sourcing Equipment (PSE) and the Powered Device (PD).

Class Usage Power Output from (PSE) Maximum Power Levels at the Powered Device (PD)
0 Default 15.4 W 0.44 - 12.95 W
1 Optional 4.0 W 0.44 - 3.84 W
2 Optional 7.0 W 3.84 - 6.49 W
3 Optional 15.4 W 6.49 - 12.95 W
4 Valid for 802.3at High PoE 30 W 12.95 - 25.5 W

 

Table 1. The minimum and maximum power levels for PSEs and PDs. Use these values when calculating the power budget of a system. Note that the maximum power available to a PD takes into account the invariable slight power loss over the network cable.

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.

Figure 6: The datasheet for AXIS P1344-E shows that with High PoE, the camera can operate at temperatures down to -40°C.

Conclusion