Frequently Asked Questions

The wire gauge you should use depends on several factors:

• Current draw: Higher current requires larger wire gauge (smaller AWG number)
• Wire length: Longer runs require larger wire to minimize voltage drop
• Operating voltage: Lower voltage systems are more sensitive to voltage drop
• Ambient temperature: Higher temperatures reduce wire ampacity
• Industry standards: Aerospace, military, and motorsport have different safety margin requirements

Our MIL-SPEC Wire Calculator helps determine the optimal wire gauge by factoring in all these variables and applying appropriate safety margins.

MIL-SPEC wire standards (such as MIL-W-22759/16) include more stringent requirements compared to commercial standards:

• Materials: Higher grade conductors and insulation materials
• Temperature ratings: Often rated for continuous operation at 150-200°C vs. 75-90°C for commercial wire
• Environmental resistance: Better resistance to chemicals, fluids, UV, and extreme conditions
• Testing: More rigorous qualification and quality control testing
• Safety factors: Higher safety margins in ampacity ratings
• Documentation: More detailed specifications and traceability requirements

These differences make MIL-SPEC wire essential for critical applications where reliability and performance under extreme conditions are paramount.

Temperature has a significant impact on wire ampacity (current-carrying capacity) for several reasons:

• Increased resistance: Copper's resistance increases approximately 0.393% per °C rise
• Reduced heat dissipation: Higher ambient temperatures reduce the wire's ability to dissipate heat
• Insulation limitations: Insulation materials have maximum temperature ratings

For example, a wire rated at 20A in a 20°C environment might only be safely rated for 15-16A in a 50°C environment.

Our calculator applies temperature derating factors based on industry standards to ensure wire selections remain safe at elevated temperatures.

The fuse size should be selected to protect the wire while allowing the circuit to operate normally:

• Standard approach: Fuses should be sized at 125% of the maximum continuous current draw
• Wire protection: The fuse must never exceed the wire's ampacity rating
• Standard sizes: Common fuse sizes are 1, 2, 3, 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 100, 125, 150, 175, 200, and 250 amps

When calculating fuse size:

1. Multiply the continuous current by 1.25
2. Round up to the next available standard fuse size
3. Verify that this size doesn't exceed the wire's ampacity

Our calculator recommends appropriate fuse sizes based on both the current requirements and the selected wire gauge.

The calculator may recommend a larger wire (smaller AWG number) than expected for several reasons:

• Voltage drop limitations: Long wire runs at high current may require larger wire to prevent excessive voltage drop, even if the current itself is within the smaller wire's ampacity
• Temperature derating: High ambient temperatures reduce a wire's current-carrying capacity
• Safety factor requirements: The selected industry (aerospace, military, motorsport) may require higher safety factors
• Wire bundling effects: Multiple wires bundled together generate more heat and require derating

For critical applications like aerospace and military systems, these conservative recommendations are essential for system reliability and safety.

The main difference between slow-blow (time-delay) and fast-acting fuses is their response to overcurrent conditions:

Fast-Acting Fuses:

• Respond quickly to overload conditions
• Offer immediate protection against short circuits
• Little tolerance for temporary current spikes
• Best for circuits with sensitive electronics

Slow-Blow (Time-Delay) Fuses:

• Allow temporary current spikes
• Designed to handle motor starting currents or inrush currents
• Still protect against sustained overloads
• Best for motors, transformers, and inductive loads

Voltage drop is the reduction in voltage along a wire due to its electrical resistance:

• Cause: All conductors have resistance, causing voltage to drop along their length
• Calculation: Voltage drop = Current × Resistance (V = I × R)
• Factors affecting voltage drop: Wire length, gauge (diameter), material, temperature, and current

Excessive voltage drop can cause several problems:

• Equipment malfunction or performance degradation
• Motors running slower or with reduced torque
• Increased heat generation in wires
• Reduced efficiency and wasted energy
• Premature component failure

For critical applications, voltage drop should typically be kept below 3%, with even tighter tolerances (1-2%) for aerospace and military applications.

For extreme environments, consider these factors when selecting wire:

Temperature Extremes:

• High temperature environments: Use wire with PTFE (Teflon) or silicone insulation, such as MIL-W-22759/16 (200°C rating)
• Low temperature applications: Select wire with insulation rated for flexibility at low temperatures, avoiding PVC which becomes brittle

Chemical Exposure:

• Fuel/oil resistance: PTFE, FEP, and ETFE insulations offer excellent resistance
• Hydraulic fluid exposure: MIL-SPEC wire typically has superior fluid resistance

Mechanical Stress:

• Vibration: Use fine-stranded wire for better flexibility and vibration resistance
• Abrasion: Consider additional mechanical protection like braided sleeving or conduit

Electrical Interference:

• EMI/RFI concerns: Use shielded wire for sensitive circuits
• Signal integrity: Twisted pair configurations can reduce noise in data lines

MIL-SPEC wire types like MIL-W-22759/16 are designed specifically for harsh conditions found in aerospace, military, and high-performance applications:

• Silver-plated copper conductors for improved conductivity
• PTFE insulation for excellent temperature and chemical resistance
• Stringent quality control and testing
• Proven reliability in extreme environments

Silver-plated copper wire offers several advantages over standard copper wire, particularly in high-performance applications:

Advantages of Silver-Plated Copper:

• Improved conductivity: Silver is the most conductive metal, with approximately 106% the conductivity of copper
• Better high-frequency performance: Silver plating reduces skin effect losses in RF applications
• Enhanced corrosion resistance: Silver plating protects the copper core from oxidation
• Superior solderability: Silver surfaces are easier to solder and maintain better conductivity at connection points
• Improved high-temperature performance: Silver plating helps maintain conductivity at elevated temperatures

Applications where Silver-Plated Copper is Preferred:

• Aerospace and military systems per MIL-SPEC requirements
• High-frequency RF circuits
• High-temperature environments
• Mission-critical applications where reliability is paramount