wire-wright

ABYC E-11 wire gauge, ampacity, and fuse sizing for small-craft DC circuits. Reads a CSV circuit list, prints a sizing table, and flags circuits whose inputs are still guesses.

npx wire-wright circuits.csv

Method

For each circuit, the conductor is the larger of:

1. Voltage-drop minimum — circular mils = 10.75 × amps × round-trip feet ÷ allowable drop volts, at 3% (critical circuits) or 10% (non-critical).
2. Ampacity minimum — smallest conductor whose allowable amperage, derated for engine spaces and bundling, carries the load (ABYC E-11 Table 6A).

The fuse/breaker is the smallest standard rating at or above 125% of a continuous load (100% if flagged non-continuous), and never above the derated ampacity of the chosen conductor — the conductor is upsized if no standard rating fits that window.

Data provenance

Ampacity values, engine-space correction factors, and bundling derates are transcribed from ABYC E-11 Table 6A as republished with ABYC's permission at https://boathowto.com/wiresize/wiresize_tables_abyc.pdf. The voltage-drop formula (K = 10.75, copper DC) is the standard E-11 method; this implementation's output is test-verified against the ABYC 3% and 10% conductor-size lookup tables from the same document (npm test).

CSV columns

| column | required | meaning | |---|---|---| | name | yes | circuit label | | amps | yes | continuous current, A | | length_ft | yes | conductor length source → device → source (round trip), ft | | drop_pct | no | 3 (default, critical) or 10 | | voltage | no | system voltage, default 12 | | engine_space | no | true/false, default false | | bundle | no | conductors bundled together, default 1 | | insulation_c | no | insulation rating °C, default 105 | | continuous | no | default true; false uses 100% fuse target | | amps_source, length_source | no | guess / spec / measured — anything not measured is flagged in output | | status | no | e.g. planned / installed — non-installed flagged | | notes | no | free text, passed through |

Limits

• DC only, copper conductors, AWG 18 through 4/0.
• Sizing is per-circuit; it does not sum loads, check panel totals, or verify fuse interrupt ratings (AIC) — lithium banks need the fuse type their battery manufacturer specifies (typically Class T).
• Output is informational. Physical installation is governed by ABYC E-11 itself and whoever surveys your boat.

License

MIT.