■ 12 & 24 volt DC planning for small boats
Circuit Locker works out boat wiring from rules you can look up: the federal ampacity table in 33 CFR 183, the 150% fuse ceiling, and the copper voltage-drop formula. Then it keeps your whole panel in one private list, with labels ready to print.
The wire check is free. The Locker Pass is $1.95 a month, $19.50 a year or $1.00 for 7 days: free during preview, nothing is charged. What it adds
10 AWG
The ampacity table would allow 18 AWG; the 3% voltage-drop limit sets it.
105 °C boat cable, outside engine spaces. The ceiling protects the wire; use the pump maker's fuse size when it is lower. Open this check
Three tools, one panel
One circuit: amps, run length, drop limit and the insulation rating printed on the cable.
What a day at anchor draws, and what it takes to put it back.
Your boat's whole circuit schedule in one list, sized and fused line by line.
Numbers you can check
No guesses dressed up as advice. Each number on a result page comes from a published table or a formula, and the method page shows the working. The assumptions that are yours to change, like how deep you discharge a battery, are labelled as assumptions.
| What | Where it comes from |
|---|---|
| Wire ampacity | 33 CFR 183.425, Table 5, by gauge and insulation rating; lowered in engine spaces (note 1) and when three or more current-carrying wires are bundled together (note 2) |
| Engine-space derating | Table 5, note 1 (0.58 to 1.00) |
| Smallest wire | 33 CFR 183.425(d)–(e): 16 AWG, or 18 AWG inside a sheath |
| Fuse ceiling | 33 CFR 183.455(c)(1): 150% of the wire's Table 5 amperage |
| Voltage drop | CM = 10.75 × amps × feet out and back ÷ volts allowed |
| Drop limits | 3% for critical circuits, 10% for the rest (ABYC practice) |
Pricing
Pricing details · Payments are not switched on yet: there is no checkout and nothing can be charged.