How do I know which fuse size to select?

A fuse is a safety device for providing over-current and short-circuit protection on an electrical circuit. Fuse selection criteria depends on the maximum current expected to flow within the electrical circuit, the recommended sizing ratio is 125% of the maximum current.

For example, a system with an expected maximum current of 100A will make use of 125A fuses. For inverter-battery systems, the charge/discharge current of the inverter determines the maximum current that will flow between the battery and the inverter.

Please refer to this document for more information. 

https://portal.segensolar.co.za/reseller/docs/Applicationnotebatterydisconnect.pdf