Do not expect a clean “add a 40-amp EV circuit” or a listed generator interlock on a residential fuse box. Contractor guidance commonly treats a fuse box, at any amperage, as something to upgrade first. Fuse panels are typically too small for modern loads, parts can be hard to match, and generator interlocks and EV breakers are made for modern breaker panels. Hire a licensed electrician; this is not a DIY add-on.
Replacement of a fuse box with a breaker panel is a different, though overlapping, job from a 100-to-200-amp heavy-up. Fixr (updated 2025-01-31) discusses fuse-box-to-breaker replacements in the same cost universe as other panel work, with a wide range depending on the new amperage. Whatever the price, the sequence is: replace and bring the service up to what the new loads need, then add the charger inlet or the generator transfer equipment under permit.
If you do not yet know the amperage, start with the “how to read the panel” page and an electrician’s inspection, not with buying a charger.
This is not a permit calculation, a utility approval, or a substitute for a licensed electrician, HVAC contractor, or the authority having jurisdiction. Panel Headroom is an independent educational site. It is not a utility, a certification body, or a contractor. Electrical and generator work that is done incorrectly can cause fire, shock, or carbon monoxide poisoning. Use the adopted electrical code and manufacturer instructions; pull permits where required.