The fuse for the T100MD+ is optional and if use, it should be attached to the +24V lead into the PLC's power supply input, not the 0V side. Since all the outputs are current sink type (i.e. they return current from the load to the power supply ground via the 0V terminal), the current drawn from the +24V terminal is mainly for powering the CPU and the inputs/outputs LED and this current (typically between 0.2 to 0.3A ) is independent of the current drawn by the NPN output load.
If there is a high current flowing into the +24V terminal it means something is wrong on the PLC circuit, probably a short circuit occurred in some components. If you have a fuse the fuse will blow to prevent further damage. However, replacing the fuse alone is probably not going to recover a failed PLC if there are permanent short-circuited components in the PLC. It just prevent more extensive damage (such as burning up of the PCB) so that the PLC would not become unrepairable due to extensively burnt PCB.
The two 10A PWM outputs on the T100MD888+ has two extra GND terminals to enable high load current to return to the power supply via the screw terminals instead of via the thin copper layer on the PCB. Actually these two GND terminals are internally shorted with the power supply 0V terminal, so if the load current is small you can actually omit to connect these two GND terminals to the power supply. But for higher current load the connection of GND terminals to the power supply 0V is definitely required to prevent interference to the PLC's power system..
