A cable size ampacity calculator helps you to find the right wire size to safely carry a given amount of electrical current.
It Depends On Conductor Type, Wire Size, Insulation Rating, Ambient Temperature, And The Number Of Current-Carrying Wires, All Based On NEC Guidelines.
Cable Ampacity Chart Copper Aluminium
| Conductor Size (AWG / mm²) | Copper (A) | Aluminum (A) |
|---|---|---|
| 14 AWG / 2.0 mm² | 15 | 10 |
| 12 AWG / 3.0 mm² | 20 | 15 |
| 10 AWG / 5.3 mm² | 30 | 20 |
| 8 AWG / 8.4 mm² | 40 | 30 |
| 6 AWG / 13.3 mm² | 55 | 40 |
| 4 AWG / 21.1 mm² | 70 | 55 |
| 2 AWG / 33.6 mm² | 95 | 75 |
| 1/0 AWG / 53.5 mm² | 125 | 95 |
| 2/0 AWG / 67.4 mm² | 145 | 115 |
| 3/0 AWG / 85.0 mm² | 165 | 135 |
| 4/0 AWG / 107 mm² | 195 | Aluminium (A) |
Wire Ampacity Calculator for Building Wiring
A wire ampacity calculator tells you the maximum current a wire can safely carry without overheating. It uses NEC tables and adjusts for things like temperature, insulation, number of wires, and how they are installed. You just enter the wire size, material (copper or aluminium), and conditions, and it gives the safe ampacity.
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Cable Size Voltage Drop & Ampacity Table
An ampacity table shows wire sizes and the maximum current they can safely carry at 86 °F for up to three wires, according to the NEC. You also need to check the voltage drop, which should stay under 3 % for branch circuits. Use this formula for single-phase circuits:
\(V_{drop} = 2 \times I \times R \times L\)where I = current, R = resistance per unit length, L = one-way wire length.
Current Rating and Cable Size Selection
In the U.S., pick a cable size based on the current needed (I = P/V), voltage drop limits, and installation conditions. Always check the NEC tables for guidance.
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Ampacity Chart for Insulated Conductors
Use NEC Table 310.15(B)(16)/(17) to find the safe current for copper and aluminium wires up to 2000 V. The table lists ampacity based on the wire’s insulation temperature rating (60°C, 75°C, 90°C).
Voltage Drop Considerations in Cable Selection
When selecting cables in the U.S., aim to keep voltage drop below ~5% of the nominal voltage, per NEC guidelines. Voltage drop increases with longer runs, smaller wires, higher current, or higher temperatures. For single-phase circuits, the formula is
\(V_{1} = 2 \times I \times R \times L\)where, I = current, R = wire resistance, L = one-way length
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Frequently Asked Questions about Cable Size Ampacity Calculator
What is ampacity, and how is it calculated?
Ampacity is the maximum current a conductor can safely carry without overheating, calculated based on conductor material, size, insulation type, ambient temperature, and installation conditions.
How do I choose the correct cable size for a current?
Select a conductor whose base ampacity meets or exceeds the load current. Then apply any required derating (temperature, bunding) and verify insulation, voltage drop, and breaker size rules are satisfied.
Can I use the same calculator for copper and aluminium cables?
Yes—calculators can handle both conductor types, but you must input the correct material because aluminium has lower conductivity and thus lower ampacity than copper.
How does ambient temperature affect cable ampacity?
Higher ambient temperatures reduce a cable’s ability to dissipate heat, so ampacity must be lowered using correction factors when temperatures exceed the reference (often 30 °C/86 °F).
What installation factors reduce cable current rating?
Bundled conductors, more than three current‑carrying cables in a raceway, poor ventilation, conduit fill, or direct burial raise heat, causing required derating.
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