§ 17
Which cable cross-section should bilge pump have when cable is 6 m long?
Answer: When you lay a new cable to e.g. an anchor winch, a bilge pump or navigation lights, the cross-section must be large enough to keep voltage drop within limit. ABYC E-11 says at most 3 % on critical circuits and at most 10 % on the rest. The calculator works backwards from current, cable length and limit to the minimum cross-section, chooses the next standard size and shows voltage drop with that. You must check the cable's current rating (how much it may carry) separately.
Mindste tværsnit A = 2 × længde × strøm × 0,0175 ÷ (spænding × tilladt fald i %)
Factor 2: current flows out in plus and home in minus
0.0175 Ω·mm²/m is copper's resistivity at approx. 20°C
Standard cross-section: 1 · 1.5 · 2.5 · 4 · 6 · 10 · 16 · 25 · 35 · 50 · 70 · 95 · 120 mm². If requirement exceeds 120 mm², 120 is shown and then the circuit must be split or voltage stepped up.
| Symbol | Meaning | Unit |
|---|---|---|
| stroem | Consumer current | A |
| laengde_m | Cable length one way (from panel to consumer) | m |
| spaending | System voltage | — |
| maks_fald | Permitted voltage drop | — |
| = | Next standard cross-section | mm² |
| = | Minimum cross-section (calculated) | mm² |
| = | Voltage drop with standard cross-section | % |
Does not apply when
The calculator's own default values inserted. The figures are calculated with exactly the formula the tool uses.
Substituted
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Når du skal trække et nyt kabel om bord, regner du baglæns fra strøm, længde og tilladt spændingsfald til det mindste tværsnit. Beregneren vælger næste standardtværsnit og viser spændingsfaldet med det.
En lænsepumpe på 20 A sidder 6 m fra tavlen i et 12 V-system.
It means: Beregnet minimum er 11.67 mm², og næste standardstørrelse er 16 mm². Med det kabel er faldet 2.2 %.
Kabinelys på 5 A, 8 m kabel én vej, 12 V. Det er en ikke-kritisk kreds.
It means: Du kan nøjes med 1.5 mm², og faldet bliver 7.8 %.
Et ankerspil trækker 80 A og sidder 10 m fra batteriet. Producenten tillader 10 % fald.
It means: Det kræver mindst 23.33 mm², så du skal bruge 25 mm². Tjek producentens anvisning for ankerspillet.
Dobbelt længde kræver dobbelt tværsnit for samme fald.
Standardtværsnittet skal være større end eller lig det beregnede.