Cable Section Calculator – Electrical Wire Sizing
Estimate copper cable section for a voltage-drop limit
How to Use
- Enter the current (amperes) your cable will carry
- Enter the system voltage (volts)
- Enter the cable length (meters)
- Set the maximum voltage drop percentage (typically 3-5%)
- Select the phase type (single or three-phase)
- Click calculate to see the voltage-drop cross-section estimate
What is Cable Section?
Cable section, also known as wire gauge or cross-sectional area, is the conductor area measured in square millimeters (mm²). Voltage drop is only one input to conductor selection.
Ampacity, insulation, protection, installation method, temperature, grouping, and local codes must be checked separately from this voltage-drop calculation.
Factors Affecting Cable Size
- Current Load: Higher currents require larger cable sections
- Cable Length: Longer cables need larger sections to minimize voltage drop
- Voltage Drop: Maximum allowable voltage drop affects minimum cable size
- Installation Method: Cables in conduits require larger sections due to heat buildup
- Ambient Temperature: Higher temperatures reduce current-carrying capacity
- Cable Grouping: Multiple cables together require derating
Understanding Voltage Drop
Voltage drop is the reduction in voltage as electrical current flows through a conductor. Excessive voltage drop can cause equipment malfunction, reduced efficiency, and overheating.
Common maximum voltage drop limits:
- Lighting circuits: 3%
- Power circuits: 5%
- Combined (distribution + final circuit): 5-8%
Installation Types
| Installation Type | Characteristics | Derating Factor |
|---|---|---|
| In Conduit | Reduced heat dissipation, most common in buildings | 0.8 |
| Open Air | Best heat dissipation, outdoor installations | 1.0 |
| Buried | Poor heat dissipation, underground installations | 0.7 |
Standard Cable Sizes (mm²)
Common standard cable sizes: 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240, 300 mm²
The next standard size shown only satisfies this voltage-drop model. It is not an ampacity or code-compliance recommendation.
Frequently Asked Questions
- What is the difference between cable section and wire gauge?
- Cable section (mm²) is used in metric systems and represents the actual cross-sectional area. Wire gauge (AWG) is used in imperial systems and is inversely related to size (higher gauge = smaller wire). This calculator uses mm² which is more intuitive.
- Why is voltage drop important in cable selection?
- Excessive voltage drop causes equipment to receive less voltage than designed for, leading to poor performance, overheating, and potential damage. Electrical codes typically limit voltage drop to 3-5% for safety and efficiency.
- Can I use aluminum cables instead of copper?
- Yes, but aluminum cables require approximately 1.6 times the cross-section of copper cables for the same current-carrying capacity due to higher resistivity. This calculator is designed for copper cables.
- Do I need to consider other derating factors?
- Yes. This calculator does not apply ampacity or installation derating. Consider ambient temperature, installation method, cable grouping, harmonic currents, protection, and local electrical codes with a qualified electrician.