High-temperature resistant copper wires such as THHN/THWN-2, MTW, XHHW-2, or tray cables are commonly recommended for distribution box wiring, chosen based on load, environment, and code compliance.

Key Considerations for Wiring Selection

1. Wire Material and Conductivity Copper is the preferred conductor due to its high conductivity, durability, and reliability under load. Aluminum can be used in some feeder circuits but requires careful termination and larger cross-sectional areas to handle the same current safely . 2. Insulation Type and Temperature Rating

• THHN/THWN-2: Suitable for general building wiring, resistant to heat, moisture, and chemicals, ideal for commercial and industrial panels .
• MTW (Machine Tool Wire): Flexible, oil-resistant, rated up to 600V, commonly used for internal panel wiring in industrial control equipment .
• XHHW-2: Cross-linked polyethylene insulation, high temperature and abrasion resistance, suitable for feeder circuits and harsh environments .
• Tray Cable (TC, TC-ER): Multiconductor, rated for ducts, conduits, and cable trays, often used in complex industrial panels . 3. Current Carrying Capacity (Ampacity) Select wire gauge based on the load current of each circuit. Ensure the cross-sectional area meets or exceeds the calculated load to prevent overheating and voltage drop . 4. Environmental and Mechanical Protection
• Indoor panels: Standard THHN/THWN-2 or MTW wires are sufficient.
• Outdoor or high-temperature areas: Use XHHW-2 or UV-resistant tray cables.
• Ensure wires are protected from physical damage, moisture, and chemical exposure . 5. Compliance with Standards
• Follow NEC (NFPA 70) in the U.S., IEC 61439 internationally, or local electrical codes.
• Use UL or CE-certified wires and components to ensure safety and inspection compliance . 6. Installation Practices
• Maintain proper grounding and bonding.
• Route wires neatly with adequate spacing and support.
• Avoid sharp bends, kinks, or exposure to heat sources.
• Label circuits clearly for maintenance and future expansion . 7. Special Applications
• Flexible power cables (DLO, welding cables) are used for generators, battery connections, or temporary power feeds .
• Explosion-proof or flame-retardant wires are required in hazardous environments .

Summary

For a distribution box, high-temperature resistant copper wires such as THHN/THWN-2, MTW, XHHW-2, or tray cables should be selected based on the load, environmental conditions, and compliance with local electrical codes. Proper installation, grounding, and labeling are equally critical to ensure safety, reliability, and long-term performance.