Aircraft Wire Voltage Drop Calculator: Compute AWG Line Loss

Calculate electrical voltage drop, remaining load voltage, and percentage line loss for mil-spec aircraft wiring profiles using FAA AC 43.13-1B standards.

The Physics of Aircraft Wire Voltage Drop

Every electrical wire possesses a small amount of native resistance to the flow of electrical current. As amperes travel down a conductor, some of this electrical energy is converted into heat and lost. This loss is known as voltage drop.

In aircraft electrical systems, minimizing voltage drop is critical. If a wire is too thin or a run is too long, the voltage reaching a component can drop below its minimum design threshold. This can cause critical avionics to reset, dim landing lights, or degrade the performance of electric fuel pumps and actuators.

FAA Regulatory Limits (AC 43.13-1B Chapter 11)

To ensure operational safety, the FAA sets maximum limits on allowable voltage drop across aircraft electrical networks. According to FAA Advisory Circular AC 43.13-1B Chapter 11, lines should be sized so that the voltage drop from the main bus to the electrical load does not exceed these general benchmarks:

• Continuous Operation Circuits: A maximum drop of 2% to 3% of the total bus voltage is typically permitted for systems running non-stop during flight.
• Intermittent Operation Circuits: A maximum drop of 5% is acceptable for systems that operate briefly (such as landing gear motors, flap actuators, or starter circuits).

Choosing the correct American Wire Gauge (AWG) size balances these electrical requirements against airframe weight savings.

Mil-Spec Copper Wire Resistance Values

The calculator evaluates circuit line loss using standard mil-spec stranded copper conductor resistance baselines. For reference, these are the exact resistance properties per 1,000 feet processed by the tool’s selection dropdown menu:

How It’s Calculated

When you select your inputs and click Calculate Voltage Propagation, the tool processes your circuit parameters through these precise plaintext steps:

1. Total Wire Resistance Resolution

The tool selects the specific resistance rating per 1,000 feet associated with your chosen AWG size. It divides that value by 1,000 to find the resistance per single foot and multiplies it by your input wire length:

Total Resistance = (AWG Resistance per 1000 Feet / 1000) * Wire Length

2. Calculated Voltage Drop

Using Ohm’s Law (V = I * R), the calculator multiplies your active circuit current load (Amperes) by the total resolved wire resistance:

Calculated Voltage Drop = Current Load * Total Resistance

3. Voltage Remaining at Load

The derived voltage drop is subtracted from your chosen aircraft bus baseline (14 VDC or 28 VDC) to display the absolute electrical force remaining at the terminal end of the wire run:

Voltage Remaining at Load = Bus Voltage – Calculated Voltage Drop

4. Percentage Line Loss

Finally, the total voltage loss is divided by the original source bus voltage supply and multiplied by 100 to show the overall efficiency loss percentage:

Percentage Line Loss = (Calculated Voltage Drop / Bus Voltage) * 100

Scope and Limitations

• Mil-Spec Copper Standard Only: The built-in resistance constants are calibrated strictly for standard mil-spec stranded copper aircraft wiring. This formula does not model aluminum wiring layout structures or alternative alloys.
• Fixed Temperature Profile: Calculations assume standard ambient operating temperatures. Because copper resistance increases as temperature rises, real-world voltage drops will be slightly higher in high-heat zones like engine compartments.
• Positive Non-Zero Rule: Inputs for current and wire length must be positive numbers greater than zero. Entering zero or negative values will block computation and trigger a parameter entry error.
• Overload Supply Guardrail: The calculator will block the output and trigger a critical validation error if the computed voltage drop mathematically exceeds the total available bus voltage supply (14V or 28V).