The big fuse right at the battery positive that protects the main cable. It is the last line of defence if a heavy cable shorts, so it sits within ~178 mm (7 in) of the terminal.
If a heavy main cable ever shorts, the main fuse is the last thing standing between a fault and a fire. It protects the biggest, most dangerous conductor in the system.
It sits right at the battery positive — within about 178 mm (7 in) of the terminal — before the cable reaches the switch or busbar.
Design your van, boat, cabin or RV system in Wattonomy and it sizes the main fuse to protect the main cable and places it at the battery positive, with the interrupting rating matched to your bank — from the appliances you actually run, sized to the recognized standard for your region. You see it on the wiring diagram, in the sized parts list, and in a plain-English build pack that explains the reasoning behind every choice. No account, no email — about a minute to a complete, validated design.
As close to the battery positive terminal as practical — within about 178 mm (7 in) — so the main cable is protected along its whole length.
Large enough to carry the system load without nuisance-tripping, but at or below the main cable’s ampacity. Wattonomy computes the rating and interrupting capacity for your design.
It takes about a minute. No account, no email.