The PTN system had been specified in terms of voltages and I did not see any reference to current.
The maximum (and minimum) voltage that had been defined in the HK standards is a sine wave between +95V and -142V (a sine wave of 75Vrms** with a DC of voltage between 40 and 48V). This voltage is encountered when the phone rings.
The PTN should supply a steady voltage of -40 to -48V when idle (compared to the other wire, which is grounded).
This power should not be used by any other electrical equipment because all equipments that are plugged into the PTN need to be cerTIfied or you would have breached the regulaTIons set by OFTA.
** 1Vrms wave is approximately a wave with amplitude of 1.4V, which is about 2.8V from the peak of the wave to the trough of the wave.