Calculator reference

Every formula CircuitProof uses, with its source. These are transcribed from the published codes; the underlying tables are pending licensed-professional verification (see FAQ).

Conductor ampacity

Base ampacity from NEC Table 310.16 (60/75/90°C columns, copper & aluminum), then derated:

• Ambient temperature correction — NEC 310.15(B)(1)
• More than 3 current-carrying conductors — NEC 310.15(C)(1)
• Capped at the termination column — NEC 110.14(C)
• Marine: ABYC E-11 Table VI (105°C, engine-space factor)

Voltage drop

DC: Vd = 2 × L × I × R ÷ 1000, with R per NEC Ch.9 Table 8. AC single-phase adds reactance: Vd = 2 × L × I × (R·cosφ + X·sinφ) ÷ 1000. Targets: 3% per NEC 210.19(A) IN; ABYC uses 3% critical / 10% non-critical (ABYC E-11.4).

Minimum wire size

The smallest AWG that satisfies both the derated ampacity requirement (×1.25 for continuous loads, NEC 210.19(A)) and the voltage-drop target for the run.

Overcurrent protection

Smallest standard device (NEC 240.6(A)) ≥ 125% of continuous + 100% of non-continuous load (NEC 210.20(A)), never exceeding the conductor it protects (NEC 240.4, with small-conductor limits 240.4(D)). Marine placement per ABYC E-11.10.

Battery bank

Ah = (Wh/day × days) ÷ V ÷ (DoD × tempFactor × inverterEff × cableEff). Default depth of discharge: 80% LiFePO4, 50% lead-acid.

Inverter

Continuous = Σ(simultaneous AC loads) × 1.2 headroom; surge = largest starting load × its surge factor + steady-state remainder.

Solar

Array watts = daily Wh ÷ peak-sun-hours ÷ system efficiency (~0.7, NREL PVWatts range). Charge-controller current ≥ module Isc × 1.25 (NEC 690.8(A)(1)).