Calculadora de Dimensionamiento de Cables
Ingresa corriente, voltaje y distancia para encontrar el tamaño mínimo de cable AWG/kcmil según código NEC. Incluye caída de voltaje, eficiencia y factores de corrección por temperatura y agrupamiento.
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What is Cable Sizing?
Cable sizing is the process of selecting the correct conductor size for an electrical circuit based on the expected load current, ambient conditions, and installation method. The National Electrical Code (NEC) Table 310.16 provides the standard ampacity ratings for insulated conductors at 30°C ambient temperature. Proper cable sizing prevents overheating, reduces fire risk, and ensures voltage at the load stays within acceptable limits. Key factors include conductor material (copper vs aluminum), insulation temperature rating (60°C, 75°C, or 90°C), ambient temperature derating per NEC 310.15(B), and conduit fill correction factors for multiple conductors sharing a raceway.
How to Use the Cable Sizing Calculator
- Enter the load current in amperes and select single-phase or three-phase
- Choose conductor material (copper or aluminum) and insulation type
- Set the ambient temperature and number of conductors in conduit for derating
- View the recommended cable size with derated ampacity and correction factors
- Switch to Voltage Drop tab to verify the voltage drop is within NEC 3%/5% limits
Frequently Asked Questions
What NEC table is used for cable sizing?
NEC Table 310.16 is the primary ampacity table for insulated conductors rated 0-2000V with not more than 3 current-carrying conductors in raceway or cable at 30°C ambient temperature. For ambient temperatures above 30°C, apply the correction factors from NEC 310.15(B)(1). For more than 3 conductors in a conduit, apply the adjustment factors from NEC 310.15(C)(1).
What is the NEC voltage drop recommendation?
NEC recommends (but does not mandate) a maximum 3% voltage drop for branch circuits and 5% for the combined feeder plus branch circuit. For example, on a 120V circuit, the maximum recommended voltage drop is 3.6V for a branch circuit. Use larger conductors or shorter runs to reduce voltage drop.
How does ambient temperature affect cable ampacity?
Higher ambient temperatures reduce cable ampacity because the conductor has less thermal headroom before reaching its insulation temperature rating. NEC 310.15(B)(1) provides correction factors: at 40°C ambient, a 75°C rated conductor retains about 88% of its 30°C ampacity. At 50°C ambient, it drops to about 75%.
When should I use copper vs aluminum conductors?
Copper has higher conductivity (about 61% IACS) and smaller diameter for the same ampacity, making it ideal for space-constrained installations. Aluminum is lighter and less expensive for larger feeders (typically 1/0 AWG and above). NEC requires aluminum conductors to be one or two sizes larger than copper to carry the same current.
How do I calculate voltage drop for a three-phase circuit?
For three-phase circuits, voltage drop = √3 × I × Z × L, where I is line current in amps, Z is impedance per unit length (considering both resistance and reactance), and L is one-way cable length. The percentage voltage drop is (voltage drop / system voltage) × 100. Keep total drop under 5% per NEC recommendation.
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