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
Every page names its nominal voltage, its one-way cable length and the current it was sized for, and shows the voltage drop that fell out. 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. None of it is guessed.
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. If a run passes through somewhere hot, pick the next size up. 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 smallest wire in the ABYC E-11 ampacity table that clears two tests at once: it carries 1.25 × 50 A without running warm (E-11's continuous-load derating), and over 3 m one way it drops no more than E-11.14.2.6 allows for this kind of circuit. Never thinner than 1.5 mm², whatever the arithmetic says — that floor is about the wire surviving vibration and handling, not current (E-11.4.1.1).
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.
The smallest rating on the standard fuse ladder at or above 1.25 × 50 A that still sits at or below what the wire can carry. The fuse is there to protect the wire, so it has to give up before the wire does.
Cranking circuits do not follow these steps. A starter pulls a very large current for a few seconds, so E-11 exempts it from the continuous-load derating and from the fuse-below-ampacity cap, and its protection is a class-T fuse sized to ride the crank. Every page says which basis produced its numbers.
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.