Respectfully, What factory wiring are you referring to?
the factory wiring to the alternator to a #4AWG,
upping the fusible link to a #8AWG,
upping the wire from the battery to the PDC to a #4AWG,
and finally upping the 2 negative wires on the battery negative post to #4AWG wires
The increase in wire size to all the wires connected to the battery (except starter) is to allow the necessary current to flow from the battery make the fusible link melt before the wires in the case of a shorted alternator to ground. Note: The negative wire(s) at the battery also need to be matched to the alternator wire.
The fusible link is protecting the battery (power source) in case the alternator shorts, it isn't protecting the downstream loads of the PDC. Protection of the downstream loads belongs to each of the individual fuses in the PDC.