How the numbers are made
Every component page keeps three things apart: what the manufacturer says about the part, what we assumed for the reference run, and what the engine worked out from those two. Here is how each one is made — and what Crimp cannot know about your boat or van.
Catalog facts
Names, models, ratings and which terminal does what come from the catalog we keep by hand from manufacturer manuals. Treat them as planning data. Before you order or wire anything, check the current manual and the nameplate on the part in your hand — revisions change, and a catalog can lag behind them.
Reference assumptions
Pages with a calculated reference name its nominal voltage, one-way cable length, design current and resulting voltage drop. Terminal and control overviews do not supply a sizing recommendation. Those are our assumptions, not your installation. Move the part, bundle the cable with others or run it through a hot space and the answer moves too.
Deterministic sizing
Sized against ABYC E-11. Boats built to UK or EU rules answer to ISO 13297 — check these figures against it before you build. The conductor table, the voltage-drop allowance, the terminal clamp and the fuse ladder are the same code the canvas runs, so a number on a page here is exactly what the canvas would give you for the same run. Results remain conditional on the supplied data and supported model.
Planning boundary
Crimp checks the circuit you draw. It cannot see the route the cable really takes, how hot your engine bay gets, how many cables share the bundle, or what your local rules add. Use the actual temperature, insulation and bundling conditions to recalculate ampacity; one size up is not a universal derating rule. And have someone qualified look over the finished installation before it goes live.
Worked example · Victron Orion XS 12/12-50
One real part, its real numbers, in the order the engine takes them. The figures below are the ones printed on that part's page — nothing here is worked out twice.
The rated output the catalog declares for this part. If a part declares neither, it gets no reference run at all — we would rather show nothing than size a cable to whatever its terminals happen to be rated for.
The reference combines the circuit’s ampacity and voltage-drop constraints over 3 m one way with any documented manufacturer minimum. The generic calculation uses a 1.25 × 50 A continuous-current margin and a 1.5 mm² floor. This model’s instructions require at least 16 mm² for the stated example route. The reference assumes 105°C copper, outside engine spaces, with no additional bundle derating. Actual routing, insulation and terminal limits still need verification.
What that wire actually drops at 12 V over 3 m one way. It is a result of the pick above, not a separate test it passed — the allowance was already one of the two constraints.
This example retains the documented 60 A fuse choice from the linked component instructions. Victron specifies a 60–70 A range for the Orion XS 12/12-50A; this example selects 60 A. A manufacturer requirement takes precedence over the generic current-based baseline. Verify the exact fuse and holder, time-current behavior, DC voltage, interrupt capacity and battery-end placement against the actual installation.
Cranking circuits use a separate model because starter current is brief and large. Crimp’s reference applies no continuous-load conductor margin and uses a separate Class T planning selection with a 250 A floor. That engine policy does not establish a universal starter-fuse requirement or prove that a fuse will tolerate a particular engine’s cranking profile.
A note on these pages
A page here can change when the catalog or the engine does. It helps you plan; a qualified installer still owns the actual route, the derating, the fault protection and whatever your local rules add.