What quota should be applied to the jumper wires of the cable tray

Jumper wires in cable trays should be sized according to the highest-rated circuit in the tray, following NEC Table 250-95, typically using #4 AWG or larger for single-conductor EGCs.

Sizing and Selection

Jumper wires, often used as equipment grounding conductors (EGCs) or bonding jumpers between cable tray sections, must be sized to safely carry fault currents without excessive voltage drop. According to NEC Section 318-3(b)(1) Exception 2, insulated, covered, or bare single-conductor EGCs of #4 AWG or larger may be used in cable trays . The exact size should correspond to the highest fuse rating or circuit breaker trip setting of any circuit in the tray, as specified in NEC Table 250-95 .

Material and Installation

• Material: Copper or aluminum conductors are commonly used, with copper preferred for lower resistance and better corrosion resistance.
• Continuity: Jumper wires must ensure electrical continuity across tray sections, especially at splice plates or tray joints. UL-listed connectors should be used to maintain reliable bonding .
• Tray as EGC: If the cable tray itself is used as the EGC, the tray's cross-sectional metal area must meet minimum requirements based on the protective device rating. If insufficient, a separate jumper wire or EGC must be installed .

Practical Considerations

• Spacing: Jumper wires should be installed to minimize mechanical stress and maintain proper separation from power and data cables .
• Durability: Wires must be tray-rated or metal-armored to withstand exposure in open-air trays .
• Bonding: For aluminum or steel trays, bonding jumpers across splice plates are generally not required if the tray is electrically continuous, but they may be added for additional safety in high-traffic or outdoor areas .

Summary

To comply with NEC standards and ensure safety:

1. Use #4 AWG or larger single-conductor EGCs for jumper wires.
2. Size according to the highest-rated protective device in the tray.
3. Ensure electrical continuity with UL-listed connectors.
4. Use tray-rated or armored conductors for durability.
5. Verify if the tray itself can serve as the EGC; otherwise, install a separate jumper wire. Following these guidelines ensures that jumper wires in cable trays provide a safe, low-impedance path for fault currents and maintain compliance with NEC Article 392 and related grounding requirements .