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Wire Ampacity Calculator

Wire gauge + load + run → NEC ampacity check and voltage drop calculation.

Where this fits

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Wire & Load

12 AWG rated at 25A handles your 16A load (64% utilized).

Rated ampacity
25A
12 AWG @ 75°C (167°F)
Utilization
64%
adequate
Voltage drop
3.17V
2.6% of 120V
End voltage
116.8V
at 50 ft
1

NEC rated ampacity

Table 310.15(B)(16) — copper, ≤3 conductors in raceway

= 25A @ 75°C (167°F)

NEC 2023 Table 310.15(B)(16)

2

Load vs. capacity

utilization = load ÷ rated × 100

= 16A ÷ 25A × 100

= 64.0% — ADEQUATE

NEC 210.19: continuous loads must not exceed 80% of breaker rating

3

Voltage drop

V_drop = 2 × I × R × L ÷ 1000

= 2 × 16A × 1.98Ω/kft × 50ft ÷ 1000

= 3.17V (2.64%)

NEC recommends ≤3% for branch circuits, ≤5% total

4

End voltage

= 116.8V at 50 ft

Within 3% limit — no upsizing needed for voltage drop

Key insight

NEC 210.19(A) requires that continuous loads (operating 3+ hours) not exceed 80% of the overcurrent protection device rating. Most residential circuits use 75°C-rated terminations — even if wire is rated higher, use the 75°C column for termination-limited circuits.

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