How much fault current a fuse can safely stop. Lithium can dump enormous current into a short, so the main fuse needs a high AIC — that is why Class T is specified at the battery.
A fuse’s amp rating is not the whole story. Its interrupting rating (AIC) is how much fault current it can actually stop — and a lithium bank can deliver far more than a cheap fuse can break.
It governs the choice of main fuse: lithium can dump enormous current into a short, so the battery fuse needs a high AIC — which is why a Class T is specified there.
Design your van, boat, cabin or RV system in Wattonomy and it computes the fault current your bank can deliver and specifies a main fuse with enough interrupting rating to clear it — 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.
The amp rating is the normal current the fuse passes; the AIC is the maximum fault current it can safely interrupt without failing. Both matter, especially on lithium.
Because a lithium bank can pour tens of thousands of amps into a dead short. The main fuse must be able to break that — hence Class T at the battery.
It takes about a minute. No account, no email.