Understanding NEC Informative Annex I: Recommended Tightening Torque Tables from UL Standard 486A-486B

Informative Annex I provides recommended tightening torque values for screw-type connections in power, lighting, control, and signal circuits. These guidelines, derived from UL Standard 486A-486B, ensure proper conductor termination and enhance connection safety.

Purpose of Annex I

• To provide default torque values when manufacturer-specific recommendations are unavailable.
• To ensure reliable electrical connections by preventing under-tightening (leading to high resistance) and over-tightening (causing mechanical damage).

Important Note: Torque checking after installation is unreliable due to normal relaxation during service. Always adhere to torque specifications during installation​.

Key Torque Tables

1. Table I.1: Torque for Screws in Power and Lighting Circuits
   • Covers screws for conductors from 30 AWG to 2000 kcmil.
   • Torque values depend on screw size and type:
     • Split-bolt connectors: For example, a 2 AWG conductor requires 275 lbf-in.
     • Other connectors: For 2 AWG, torque is 150 lbf-in​.
2. Table I.2: Torque for Smaller Screws (< No. 10)
   • Includes screws for conductors up to 8 AWG.
   • Example: A slot width ≥ 1.2 mm for a 5/32-inch slot length requires 12 lbf-in torque​.
3. Table I.3: Torque for Allen or Square Drive Screws
   • Provides torque for screws with recessed drives based on socket width.
   • Example: A 3/16-inch drive requires 120 lbf-in torque​.

Applications

1. Power and Lighting Circuits
   • Ensures secure connections for larger conductor sizes in electrical panels, lighting circuits, and distribution systems.
2. Control and Signal Circuits
   • Prevents connection failures in sensitive low-voltage or control wiring.
3. Split-Bolt and Recessed Drive Connections
   • Provides values for specialized connectors and drive mechanisms used in industrial settings.

Recommendations

1. Follow Manufacturer Guidelines First
   • Use Annex I tables only if specific torque values are not provided by the equipment or connector manufacturer.
2. Use Proper Tools
   • Employ calibrated torque wrenches or drivers for accuracy.
3. Avoid Post-Installation Torque Adjustments
   • Post-installation checks are unreliable due to relaxation in connections over time.

Conclusion

NEC Informative Annex I ensures proper electrical connections by providing standardized torque values. By preventing loose or overtightened connections, these recommendations enhance system reliability and safety.