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Wire Size Calculator (AWG & mm²)

ДанныеМатематика

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ВХОД

Автоматический процесс

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Load Current *

Supply Voltage *

One-way Cable Length *

System

Voltage System

Conductor Material

Installation

In Conduit uses NEC 310.16 ampacity. Free Air uses NEC 310.17 (higher). Direct Burial is derated to 85% of conduit.

Max Voltage Drop

NEC recommends ≤3% for branch circuits, ≤5% combined feeder + branch.

ВЫХОД

Клиентская сторона

Свойство	Ценить
Recommended Wire (AWG)	-
Cross-section (mm²)	-
Wire Ampacity	-
Voltage Drop	-
Voltage Drop (%)	-
Voltage at Load	-
Power Loss (heat)	-
Voltage Drop Formula	-

Enter your load values to get a wire size recommendation.

AWG Reference Table

Shows AWG sizes from 14 down to 4/0 with ampacity and the voltage drop your circuit would have at each size. The recommended size is highlighted.

AWG	mm²	Ampacity (A)	V-Drop (V / %)
Результат появится здесь

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Wire Size Calculator (AWG & mm²)

Pick the right copper or aluminum conductor for any DC, single-phase AC, or 3-phase AC circuit. Enter your load current, supply voltage, and one-way cable length and the calculator iterates the NEC ampacity table to find the smallest wire that handles the load и keeps voltage drop under your limit. Choosing a wire that is too small wastes power as heat, sags the voltage at the load, and is a real fire hazard — yet it is exactly the kind of decision generic AI chatbots get wrong because they confuse the NEC 310.16 and 310.17 tables or misquote resistance values.

Как использовать

Введите load current in amps. For motors and resistive loads use the rated full-load current.
Введите напряжение источника at the source (e.g. 12, 24, 120, 240, 480).
Введите one-way cable length from source to load. Pick feet or meters from the dropdown — the calculator round-trips internally for DC and single-phase, and uses the line-to-line factor (√3) for 3-phase.
Выберите voltage system: AC single-phase, AC 3-phase, or DC.
Выберите conductor material. Aluminum is cheaper but needs roughly one AWG size larger for the same current.
Выберите installation method. Free Air uses NEC 310.17 ampacity (higher because heat dissipates), In Conduit uses NEC 310.16, and Direct Burial derates the conduit value by 15 % to account for soil thermal resistance.
Set your max acceptable voltage drop percent. NEC recommends ≤ 3 % for branch circuits and ≤ 5 % combined feeder plus branch.
The recommendation appears instantly, along with the full AWG reference table showing the voltage drop your run would have at every standard size from 14 AWG up to 4/0.

Возможности

Copper and aluminum — separate resistance and ampacity tables for each material.
DC, single-phase AC, and 3-phase AC — correct round-trip and √3 factors automatically.
AWG and mm² output — recommended size shown in both North-American AWG and IEC mm² cross-section.
Voltage drop guard — calculator rejects any size whose drop exceeds your percent limit, even if ampacity passes.
NEC 310.16 / 310.17 ampacity — real reference data, not generic estimates. Free Air uses the higher 310.17 table.
Direct-burial derating — installation type adjusts ampacity to account for soil and conduit heat dissipation.
Power loss display — see how many watts your cable is dissipating as heat.
Full AWG reference table — every standard size from 14 AWG to 4/0 with the actual voltage drop your circuit would have at that size, color-coded for pass / under-ampacity / drop-exceeds-limit.
100 % client-side — calculations run in your browser, nothing is sent to a server.

 Часто задаваемые вопросы

Why does voltage drop matter when the wire can handle the current?

Ampacity tells you when a wire will overheat and become a fire risk, but a wire that survives thermally can still drop so much voltage along its length that the equipment at the far end gets too little voltage to run properly. Motors brown out and run hot, LEDs dim, and sensitive electronics misbehave. The NEC voltage drop recommendation (3 % branch, 5 % combined) exists to keep the delivered voltage close enough to nameplate that the load works as intended over the wire's lifetime.
Why does aluminum need a larger gauge than copper for the same current?

Aluminum has about 61 % of copper's conductivity by volume, so to carry the same current with the same voltage drop you need roughly 1.6× the cross-sectional area. In practice that means going up about one AWG size: where copper handles a load at 10 AWG, aluminum typically needs 8 AWG. Aluminum is still common in large feeders because it is much cheaper per amp delivered — the trade-off is bigger conduit and slightly larger terminations.
Why is the 3-phase formula different from single-phase or DC?

In single-phase and DC the current has to travel out on one conductor and back on another, so the total resistive path is 2 × length × resistance per unit. In a balanced 3-phase wye system the three phase currents return through each other, so there is no separate neutral return path. The voltage drop between phases works out to √3 ≈ 1.732 × length × current × resistance, which is less than 2× — that's part of why 3-phase distribution is more efficient than single-phase for the same delivered power.
Why does the same wire have a higher ampacity in free air than in conduit?

Current flow heats the conductor through I²R losses. In free air the heat radiates and convects away into the surrounding atmosphere on all sides. Inside a conduit, the conductor is surrounded by other current-carrying wires and trapped air, so heat builds up faster and the insulation hits its rated temperature sooner. NEC 310.16 (in conduit) and 310.17 (free air) give different ampacities for the same conductor for exactly this reason — typically 25 % to 50 % higher in free air.
What is the difference between AWG and mm²?

AWG (American Wire Gauge) is a legacy logarithmic numbering system where lower numbers mean thicker wire — 14 AWG is thinner than 10 AWG, which is thinner than 4 AWG. Each 3 AWG steps roughly doubles the cross-sectional area. mm² (square millimeters) is the IEC metric equivalent and names the conductor by its actual cross-sectional area: 14 AWG is about 2.08 mm², 10 AWG is about 5.26 mm². Most of the world uses mm²; the US and Canada use AWG.