Critical
Don't build this as drawn
A short that nothing can clear, a fuse that welds shut, a device on the wrong voltage. Fix it on the drawing before you buy a metre of cable.
Diagnostics reference
Every check Crimp runs on a 12 V drawing
The front page tells one story, the DC-DC charger that would have cooked a small alternator. That is one of 51 checks that run on every drawing, as you draw. This is the whole list, grouped by what each one protects you from.
Checked Sep 4, 2026 · 12 V DC planning · your manual wins
Reading a finding
Three severities, one meaning each.
The colour says how much of the drawing to trust while the finding stands. It is chosen by physical consequence, not by how hard the fix is.
Warning
It works, but not as intended
A run that sags, a fuse that nuisance-trips, a bank that ages unevenly. Often a real choice you're making; the finding makes sure you're making it on purpose.
Note
Something to confirm
A guessed length that decides a gauge, a part the assistant picked for you, a battery with no chemistry set. Nothing is wrong yet, but a number is resting on an assumption.
14 checks
Fuses and protection
Whether every conductor has a fuse that will open before the wire does, sits where a short can't get in front of it, and is a part that can actually be bought.
Critical
A positive run with no fuse anywhere on the path
A short on this cable melts it before anything trips. Every positive conductor leaving a battery needs a fuse; ABYC E-11 exempts only the engine cranking conductor.
Critical
A charging source's positive output reaches the battery unfused
The output cable of an alternator, a solar controller or a charger is a battery conductor too. A chafe anywhere on it dumps the bank's full short-circuit current with nothing to stop it.
Critical
A charger's BATT+ output reaches the battery unfused
Same fault as above, called out separately because the charger's manual usually shows the fuse and the drawing forgot it. ABYC E-11 wants the fuse within 7 in of the battery.
Critical
The feed cable into a fuse block is itself unfused
The slot fuses protect each branch, not the trunk that feeds them. If that trunk chafes on the way to the block, nothing opens.
Critical
A fuse-block slot is carrying a load with no rating picked
Until a rating is chosen the slot is a straight connection. The branch cable behind it can melt before anything trips.
Warning
A lithium battery has no fuse on its positive post
A lithium bank can deliver five to ten thousand amps into a short. With the first fuse further than 175 mm from the post, that conductor carries all of it until something else gives way.
Warning
The first fuse sits too far from the battery
ABYC E-11 wants the fuse within 175 mm along the conductor from the positive post. Everything before the fuse is unprotected cable.
Critical
A fuse rated above what its wire can carry
The fuse lets that current flow indefinitely, but the conductor's continuous ampacity is lower. The insulation cooks before the fuse opens. Fit a smaller fuse or a fatter wire.
Critical
A branch is relying on the battery's main fuse to protect a thin wire
The terminal fuse is sized for the bank's worst-case fault, not for a 25 A branch. That branch needs its own fuse near the load, not a fatter wire to suit a 300 A MRBF.
Warning
A fuse rated below the current its run actually carries
The devices downstream draw more continuously than the fuse will hold. Adding a starter or an inverter raises every fuse on the path back to the battery.
Critical
A fuse that can't break the bank's fault current
Every fuse family has an interrupt rating. A blade fuse breaks about 1,000 A; a lithium bank can deliver ten times that. Past its rating the fuse welds shut instead of opening. A properly rated fuse in series ahead of it counts, and then this drops to a note.
Warning
Fused runs on a high-fault bank don't say which fuse family
On a bank that can out-deliver the weakest family's interrupt rating, the type decides whether the fuse opens or welds. Without one, the interrupt and availability checks can't run.
Warning
A fuse rating nobody makes in that family
The circuit sized at 10 A behind MEGA slots gets a 40 A fuse fitted, because that is the smallest MEGA you can buy. The drawing still shows a fuse; the wire is protected well above what it was sized for.
Critical
Lynx branch fuses add up to more than the module allows
Victron limits the total of the circuit fuses on a Lynx chain to the lowest-rated module in it. Above that, the bus bar itself is the weak point.
4 checks
Wire, terminals and voltage drop
Whether each run and the stud it lands on can carry the current for as long as it flows, and whether the load at the end still sees enough volts.
Warning
A wire too thin for the continuous current on it
ABYC E-11 wants conductor ampacity above the continuous load with headroom. This run falls short, and without a fuse at or below its ampacity the conductor can overheat before anything trips.
Warning
Too much voltage lost between the battery and a load
Each cable on its own may pass, but the whole path from battery to load adds up. The threshold is that circuit's own ABYC E-11 allowance, 3 % on critical circuits and 10 % on general lighting, not one fixed number.
Critical
A cable carrying more than the stud it lands on is rated for
The conductor was sized for the current; the switch contact or bus stud was not. It heats at the lug and can fail long before any fuse notices.
Note
Two cables between the same parts with very different lengths
Cables between the same pair of components normally share a route, so a big difference is usually a typo. The longer length is the one voltage drop should be judged on.
9 checks
Charging sources
Whether the alternator, the DC-DC, the shore charger and the solar controller are matched to each other and to the bank they feed.
Critical
A DC-DC charger pulling more than the alternator can supply
Above half the alternator's continuous rating it runs hot at idle; past three quarters it will eventually cook. Only chargers whose input actually reaches the alternator are counted.
Critical
A DC-DC charger fed straight from the alternator with no battery on that bus
Nothing clamps the charger's input and nothing absorbs the alternator's load-dump transient. The first start without the start battery online takes out the regulator or the charger.
Warning
Combined charging current above what the bank will accept
Lead-acid is pushed above 0.3 C, lithium above 0.5 C, unless the battery's own maximum charge current says otherwise. On lead-acid that is a warning; on lithium the BMS usually saves the day, so it is a note.
Critical
An inverter that can draw more than the bank can deliver
The inverter's full-load current is above the bank's continuous discharge limit. Expect voltage sag under load and a BMS that cuts out mid-cycle.
Critical
A solar string whose cold-morning open-circuit voltage exceeds the controller's limit
Panel voltage rises as temperature falls. The longest string is checked at −25 °C using the NEC 690.7 correction; above the controller's maximum PV input, the first cold sunrise fries it.
Warning
A charger fed from the engine's starter terminal instead of the alternator output
That cable is sized for cranking surge and won't show alternator current when the engine runs. Charging devices belong on the alternator's B+ output.
Critical
A DC-DC charger's output landed on the same bus its input draws from
As drawn, the charger is trying to top up the battery that powers it. Its output belongs on the separate house bank.
Critical
A charger's input and output both reach the same battery
The charger would be charging the bank whose current feeds it. It refuses to run, or cycles losses through itself. The output belongs on a different battery.
Warning
A charger whose negative never reaches the battery
The positive is wired but the return isn't, or lands on something that goes nowhere. Without a path back the charger can't deliver a single amp.
13 checks
Wiring mistakes
The drawing errors that would be a dead short, a shock hazard or a device that never turns on.
Critical
A positive terminal wired straight to a negative
Energising it is a dead short. Cables vaporise before any fuse can react.
Critical
A live AC conductor landed on a DC rail
Mains potential then sits on every DC device and, through the bonding system, on the hull. No DC fuse will clear it. ABYC E-11 keeps AC and DC conductors apart; the only permitted link is the AC grounding conductor to DC negative.
Critical
A device rated for one voltage sitting on a rail of another
A 12 V device on a 48 V rail is destroyed instantly; a 48 V device on 12 V never starts. It needs a converter on the correct rail.
Critical
Two different voltage rails bonded together with no converter
Everything on the lower-voltage side sees the higher voltage the moment the system is switched on.
Warning
A ground terminal that carries fault current is not bonded
A case or chassis terminal exists to give fault current somewhere to go. Left unconnected, the fault goes through whatever touches it.
Warning
A load with no path to either battery terminal
It is on the drawing but not in the circuit, so it won't power on and nothing has been sized for it.
Warning
A load whose negative is wired but whose positive never reaches a battery
Half a circuit. The load stays dark until the positive side is closed.
Warning
A load whose positive is wired but whose negative never gets back
The other half. Current has nowhere to return, so the load stays dark.
Warning
A load fed through a converter that isn't itself wired to a battery
The load is connected correctly to the converter, but the converter has no supply yet, so neither does the load.
Critical
A voltage-sense lead being used as a bus
A monitor's sense terminal only measures. Two cables on it, or two battery positives joined only through it, means real current through a wire rated for one amp, unfused and unsized.
Warning
A cable marked as a series link between things that aren't like cells
Series jumpers make sense between batteries or between solar panels. Anywhere else, positive to negative is still a short.
Warning
More than one cable between the same two terminals
Almost always left over from editing. The duplicates carry no extra current and clutter the schedule.
Critical
A cable ending on a terminal the part doesn't have
Usually from a part that was swapped or a file that was edited by hand. It is drawn but connects nothing, so whatever it feeds is missing from every number.
5 checks
Battery banks
Whether batteries wired in parallel or in series actually behave as one bank.
Warning
Parallel batteries with unequal cable lengths
When the interconnects differ by more than 20 %, the battery on the shorter run hogs the charge and the discharge. It ages first and the bank's capacity follows it down.
Warning
Lithium and lead-acid batteries in parallel
They rest at different voltages and follow different curves, so one dumps current into the other whenever the system is idle. The lead bank wears out fast and the lithium cells see charge profiles they weren't designed for.
Warning
Series-stacked batteries with different voltages
The smaller cell discharges into the larger one every cycle, sags below its floor and eventually reverses. Series strings need matched cells.
Warning
A battery rail above the 60 V DC touch-safe limit
Ordinary tinned marine cable and most distribution blocks are not rated for hot-touch above 60 V. If the stack was meant to be that tall it needs special insulation and lockout; if it wasn't, drop some cells.
Note
A battery with no chemistry set
Its fault current and charge acceptance are unknown, which is not the same as zero. The interrupt-capacity and acceptance checks skip this bank until a chemistry is chosen.
2 checks
Energy budget
Whether the bank lasts the day on what the loads draw and the sources put back.
Note
No battery in the system yet
Without one there is no runtime, autonomy or charging time to estimate.
Warning
Loads with nothing putting energy back
The budget shows what the loads take per day and how many days the bank lasts with no source at all.
4 checks
Things left to confirm
Numbers that came from an estimate rather than a datasheet, so you know which ones to check before you buy.
Warning
A custom part whose declared currents can't describe a real device
A surge below the continuous draw, or an engine whose surge is so far above its draw that the two look swapped. These numbers feed every sizing decision, so they are checked before anything is sized from them.
Note
Parts whose specs were recalled by the assistant, not read off a datasheet
Everything downstream is computed from those figures, so a wrong nameplate number gives a wrong answer that still looks checked. One note lists them all.
Note
Parts the assistant picked because you didn't name one
The specs are the catalog's, but they describe the part it chose, which may not be the one you're buying. Swap in yours and the note clears itself.
Note
Guessed run lengths that actually decide a wire size
Only the runs where the length picked the gauge are listed. A short bus jumper's guess can't change a number, so it isn't in the way.
Where the rules come from
One standard ran. Your manual still wins.
Sized against ABYC E-11. Boats built to EU rules answer to ISO 13297 — check these figures against it before you build.
Where Crimp takes over
What the checks deliberately don't do.
They don't model conductor impedance, so a bank's fault current is the same figure everywhere on the drawing. They don't coordinate two fuses in series, only confirm that the upstream one can break the fault. They have no AC model: an AC run is sized by its inlet rating and left to the inlet's breaker. And they never guess a fuse family or a chemistry for you, because a guess that sizes a wire is worse than a note that asks.
Run them on your own drawingStill yours to know
How hot the engine bay gets, whether a run is in conduit, what the surveyor for your flag state will ask for, and the exact limits printed in the manual for the part in your hand. Where a finding cites a number, check it against that manual before you buy.
Victron EnergyWiring Unlimited: DC wiringThe plain-language reasoning behind fusing every battery conductor, keeping parallel interconnects equal, and why a DC-DC belongs behind a battery.Blue Sea SystemsSelect a fuse and fuse holder for your DC product installationWhere the 7 in rule comes from in practice, and how a fuse's interrupt rating is matched to the battery that feeds it.LittelfuseFuseology selection guideInterrupt ratings and the ampere ranges each fuse family is made in, which is what the interrupt and availability checks are built on.American Boat & Yacht CouncilStandards Update, Supplement 65ABYC's own notice of the current E-11 revision. The standard itself is sold, not published, so this is the public pointer to the edition the checks follow.