Default Class (Class 0)
The reason we can skip classification altogether in some cases is that the IEEE standard specifies a default value of power—one that we can assign to any unknown PD and would be at least “safe,” because it is based on the worst-case assumption of a CAT3 cable. That default value is 12.95 W (on the PD side), which translates to 15.4 W on the PSE-side; see Fig. 4.2. It is the equivalent of “no class,” or equivalently Class 0.
FIGURE 4.2 PoE power-classification levels.
But this is also the maximum power as per the ...