High-voltage and low-voltage cables should be run together in cable trays

High-voltage and low-voltage cables should generally be separated in cable trays to prevent interference, ensure safety, and comply with NEC and industry standards.

Separation Requirements

High-voltage (power) and low-voltage (control, signal, or instrumentation) cables should not be routed together in the same tray without proper separation. Mixing these cables can cause electromagnetic interference (EMI), cross-talk, signal distortion, or even equipment damage in dense or congested installations . Industry best practices recommend:

• Separate trays or compartments for different voltage classes.
• Vertical or horizontal spacing of at least 12 inches (300 mm) between power and control trays when possible .
• Divider brackets or metal partitions if cables must share a tray due to space constraints .

Code Compliance

The National Electrical Code (NEC) provides specific rules for mixed-voltage installations:

• NEC 300.3(C), 725.136, 760.53/760.136, and 805 outline routing and separation requirements for Class 1, 2, and 3 circuits .
• NEC 392.20(B) allows high-voltage cables (>600V) to share a tray with lower-voltage cables only if:
  • The high-voltage cables are Type MC, or
  • A fixed solid barrier compatible with the tray material is installed between voltage classes .
• Class 2/3 circuits cannot share space with Class 1 circuits unless reclassified and installed using Class 1 wiring methods .

Practical Layout Considerations

• Electrical on top, instrumentation below: Positioning high-current power cables above sensitive low-voltage cables reduces EMI .
• Straight, accessible pathways: Minimize bends and crossovers to reduce cable wear and simplify maintenance .
• Shielded cables: While shielding can reduce interference, it does not replace required spacing or NEC separation rules .
• Future expansion: Leave spare capacity and access routes to accommodate additional cables safely .

Summary

Routing high-voltage and low-voltage cables together without separation is not recommended. Use separate trays, dividers, or barriers to maintain safety, reduce EMI, and comply with NEC and IEC standards. Proper planning ensures reliable operation, easier maintenance, and inspection readiness.