About MIL-SPEC 22759/16 Wire Sizing

Understanding MIL-SPEC 22759/16 Wire Standards

Military Specification (MIL-SPEC) wire standards are critical guidelines for the design and selection of electrical wiring in aerospace, defense, and other high-reliability applications. These standards ensure that wiring systems meet stringent requirements for safety, reliability, and performance in demanding environments.

This calculator specifically uses data from MIL-SPEC 22759/16, which is a specification for aerospace-grade wire with fluoropolymer insulation. These wires are designed to withstand extreme conditions, including high temperatures, mechanical stress, and chemical exposure.

Updated Current Ratings: This calculator now includes the latest current ratings for MIL-SPEC 22759/16 wire, providing more accurate ampacity values for all wire gauges from 24 AWG to 2/0 AWG. These values have been sourced from manufacturer specifications for high-temperature rated aerospace wire.

Wire Gauge Selection Factors

Current Capacity (Ampacity)

The primary factor in wire selection is its ability to carry the required current without overheating. The ampacity of a wire depends on:

  • Wire gauge (AWG size)
  • Insulation temperature rating
  • Ambient temperature
  • Bundling conditions
  • Installation method

Our calculator applies a 150% safety factor to the peak current to ensure the wire can handle transient loads and has adequate margin, following military specifications.

New Feature: The calculator now also shows an alternative wire size calculated at 100% of peak current (without the safety factor). This comparison helps you understand the trade-offs between following the full MIL-SPEC requirements and using a smaller wire that may be sufficient for non-critical applications where weight and space are primary concerns.

Temperature Derating

The current-carrying capacity of a wire decreases as the ambient temperature increases. Our calculator applies appropriate derating factors based on the MIL-W-5088 standard:

Temperature (°C) Derating Factor
201.00
400.88
600.75
800.58
1000.33

Voltage Drop

Voltage drop is the reduction in voltage along a wire due to its inherent resistance. It's calculated using Ohm's Law: V = I × R, where:

  • V = Voltage drop (volts)
  • I = Current (amperes)
  • R = Wire resistance (ohms)

In critical applications, it's recommended to keep voltage drop below 3% of the system voltage. Excessive voltage drop can cause equipment malfunction or damage.

Fuse/Circuit Breaker Sizing

Protective devices should be rated to:

  • Allow normal operation without nuisance tripping
  • Protect the wire from overheating during overcurrent conditions
  • React quickly enough to prevent damage to equipment

Our calculator recommends a fuse size that is 125% of the peak current, then rounds up to the next standard fuse size. This sizing prevents nuisance tripping while still providing adequate protection.

American Wire Gauge (AWG) System

The AWG system is a standardized wire gauge system used in North America. In this system:

  • Smaller AWG numbers indicate larger wire diameters
  • Each 3-gauge decrease approximately doubles the cross-sectional area
  • Each 6-gauge decrease approximately doubles the diameter

For very large sizes, the designation changes to MCM (thousand circular mils) or kcmil (thousand circular mils). Sizes larger than AWG 1 are denoted as 1/0 (pronounced "one-aught"), 2/0, 3/0, etc.

Common AWG Sizes in Aerospace Applications

AWG Size Diameter (mm) Resistance (Ω/1000ft) Typical Applications
4 5.19 0.28 Main power distribution, starter cables
6 4.11 0.445 Battery cables, main power buses
8 3.26 0.701 Alternator wiring, heavy-duty circuits
10 2.59 1.26 Landing gear motors, hydraulic pumps
12 2.05 2.02 Fuel pumps, cabin lighting circuits
14 1.63 3.06 Position lights, avionics cooling fans
16 1.29 4.81 Instrument lighting, low-power devices
20 0.81 9.88 Avionics signal wiring, sensors
22 0.64 16.2 Data bus wiring, low-current signals

Special Considerations for Aircraft Wiring

Important Safety Notice

This calculator is provided as a reference tool only and should not be the sole basis for critical aerospace or military wiring decisions. Always:

  • Consult the latest version of relevant military standards and specifications
  • Follow manufacturer recommendations for specific devices
  • Verify calculations with a qualified aerospace electrical engineer
  • Consider all environmental factors specific to your application
  • Comply with all applicable regulations and certification requirements

Altitude Effects

At higher altitudes, the reduced air density affects heat dissipation from wires. For altitudes above 60,000 feet, additional derating factors should be applied.

Electromagnetic Interference (EMI)

For sensitive electronic equipment, shielded wire may be required to prevent EMI issues. Always separate power and signal wiring according to applicable standards.

Vibration Resistance

Aircraft wiring must withstand significant vibration. Use proper strain relief, support, and routing techniques to minimize fatigue and chafing.

Fire Resistance

Aerospace wiring typically requires specific fire resistance properties. Ensure that selected wire meets all applicable flammability and smoke emission requirements.

References and Further Reading

  • MIL-W-22759/16 - Military Specification for Fluoropolymer-Insulated Wire
  • MIL-W-5088 - Military Specification for Wiring, Aerospace Vehicle
  • AS50881 - Aerospace Standard for Wiring Aerospace Vehicles
  • FAA Advisory Circular 43.13-1B - Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair