Don't think Parallax provides a drawing for the 5355 power center. However they do provide a website that answers your question.
This is Parallax's answer to your question:
A: These fuses protect the converter from damage in the event of a reverse polarity scenario. In the event the battery or batteries are connected backwards, the two 30A ATC fuses will blow to protect the converter. Before replacing a converter suspected of being inoperative, always check these fuses first! These are standard automotive type 30 amp fuses.