And 48v is the nominal unloaded voltage supply. The P48 spec calls for an unloaded 48v±4v at the terminals, so you can get between anywhere between 44v and 52v. The voltage at the mic, once the P48 is 'loaded' is normally a lot lower.

The power is supplied through a pair of 6.81k resistors per channel (which should ideally be matched to within <0.5% to get the best common mode noise rejection). The resistors limit the maximum current that can flow to ground (if the mic lead is shorted) to about 15mA to a) hopefully stop the short affecting other microphones and b) reduce the risk of excess current overheating components and risking possible component failure or even fire. Of course the main desk P48 supply has to be capable of supplying 15mA or over, otherwise the P48 power will still be maxed out.

But once current starts flowing through those resistors, you'll get a voltage drop across them, about 3.4v per mA draw (as the current is split across two resistors), so the voltage at the mic will always be lower than the nominal voltage, and can drop right down to 10v dc for a mic that draws the maximum allowable 10mA of current if the nominal voltage starts at 44v DC.