DC Wire Size Calculator
Calculating the DC wire size is vital for budgeting any electrical project, as a bigger wire size implies more expensive cables. For that reason, we've created this tool.
As an example of how to size a DC wire, we'll calculate the wire size for a 200 amp DC system using this calculator.
You can additionally look at the FAQ section for other numeric examples, like what wire size for a 12V DC you should use.
How to calculate the size of a DC wire
The formula to calculate the wire size of a DC system is:
A = (2DIϱ) / V,
- V — Voltage drop between the source and the farthest end of the wire, measured in volts;
- I — Current running through the wire, in amps;
- ϱ — Resistivity of the conductor material, in ohm × meters;
- D — One-way distance (how far is the cable run from its source to the farther point), in meters;
- A — Cross-sectional area of the wire, in square meters; and
🙋 Important remarks:
- The 2 coefficient before D accounts for the return path after the current passes the load.
- V is the product of the allowable voltage drop percentage and the source voltage.
- ϱ is not constant; it varies with the operating temperature.
- For source voltages above 50 V, if L<16 m, this calculator assumes a distance of 16 m so that for small lengths, the wire doesn't result in excessively tiny sizes.
Example: How to size a DC wire of 200 amp
Suppose an electrical system with a 120 V source and allowable drop of 3%, a copper cable with a maximum temperature of 50°C, operating at 200 amps at DC. The **wire size is unknown, and the one-way distance (from source to load) is 50 m.
Follow these steps to know the wire size:
- In the DC wire size calculator, input:
- Source voltage: 120 V;
- Allowable drop: 3%;
- Material: Copper;
- Current: 200 A;
- Distance (D): 50 m; and
- Maximum temperature: 50°C.
- That's it. The wire size for your 200 amp DC system should be 104.65 mm², or AWG = 0000 (4/0)
- You can check your results using the formula presented in the previous section.
Other useful tools like the DC wire size calculator
What wire size for a 12V DC should I use?
The wire size for a 12 V DC depends mainly on the current and the wire length. Follow these steps to calculate it:
- Determine the electric current I (i.e., 20 A), cable length L (i.e., 5 m), conductor resistivity ϱ (typically 2.22 × 10⁻⁸ Ω⋅m for copper), and voltage drop V (typically 3% of the source voltage).
- Input the values in the formula:
A = (2IϱL) / V = (2 ⋅ 20 ⋅ 2.22 × 10⁻⁸ ⋅ 50) / (0.03 ⋅ 12 V)
- The result should be 0.0001235 m² or 123.5 mm².
What size wire for 30 amp DC should I use?
The wire size for a 30 amp DC depends primarily on the source voltage and the wire length. Follow these steps to calculate it:
- Determine the source voltage (i.e., 12 V), cable length L (i.e., 50 m), conductor resistivity ϱ (typically 2.22 × 10⁻⁸ Ω⋅m for copper), and voltage drop V (typically 3% = 0.03 of the source voltage).
- Input the values in the following formula:
A = (2IϱL) / V = (2 ⋅ 30 ⋅ 2.22 × 10⁻⁸ ⋅ 50) / (0.03 ⋅ 12 V)
- The result should be 0.00018525 m² or 185.25 mm².
These results are only a guide for informational purposes. Always consult a qualified electrician before proceeding with any electrical installation.