The fitting of adequate fuses or circuit protection in all DC circuits is essential. the DC fuse size must be big enough to carry the maximum expected current, but not over-sized for the current rating of wire used. The reason for a fuse is to protect the circuit. Correct cable sizing is also incredibly important.
Suitably rated fuses of the types listed below should be used between the battery and load or charge circuits, placed as close as possible to the battery. DC fuse size is based upon the length of time the maximum current will occur taking into account surge ability of the inverter or other devices.
Currents need to be 10% to 20% lower than fuse ratings to avoid nuisance fuse blowing. Also inverter efficiency needs to be considered. eg. if this is 85% at high load a 3 kW AC load would draw 3450 W from the DC battery, (ie. 288 A @ 12 V; 144 A @ 24 V).
DC rated circuit breakers can also be used. These can then act as safe and convenient disconnect switches if servicing is required.
In all on our 12v solar panel kits we supply to correctly sized cable and DC fuse size.