Grounding Requirements for Cable Trays

1. General Requirements & Scope

• Metal cable trays must be grounded:
   
  Steel, hot-dip galvanized, stainless steel, and aluminum alloy trays shall be reliably connected to the PE protective conductor and bonded equipotentially to prevent electric shock.
• Non-metallic trays:
   
  Polymer, FRP, and composite non-conductive trays generally do not require grounding.

2. Quantity and Spacing of Grounding Points (Mandatory)

3. Connection, Bridging and Bolt Requirements (By Tray Type)

A. Non‑galvanized / Spray‑painted / Powder‑coated Cable Trays

• Each connection plate must be bridged at both ends.
• Jumper wire: copper flexible conductor ≥ 4 mm² (or as designed).
• Paint/coating must be removed at grounding contact surfaces to ensure metal‑to‑metal contact.

B. Galvanized Cable Trays (Hot-dip / Electro-galvanized)

• Jumper wires are not required if bolted connection is reliable.
• Each end of the connection plate shall be fixed with at least 2 bolts equipped with lock washers or lock nuts.
• Contact surfaces shall be cleaned to ensure conductivity (contact resistance ≤ 0.00033 Ω).

4. Special Conditions & Supplementary Grounding Requirements

Expansion Joints / Deformation Joints

• Steel trays > 30 m and aluminum alloy trays > 15 m shall be provided with expansion joints.
• At building deformation joints: use flexible braided copper wire ≥ 16 mm² to maintain grounding continuity.

Multi‑layer Cable Trays

• A grounding main bar (e.g., 40×4 galvanized flat steel or bare copper) shall be installed along the tray length.
• Each layer and each segment shall connect to the main grounding bar at least once.
• Interlayer bridging: connect upper and lower layers with ≥ 16 mm² jumpers approximately every 6 m.

Grounding Resistance

• Independent protective grounding: ≤ 4 Ω.
• Combined with lightning protection grounding: ≤ 1 Ω.

5. Construction & Acceptance Key Points

• The entire metal tray system must form a continuous electrical path.
• Connection bolts shall be securely fastened; nuts shall be installed on the outside; 2–3 exposed threads are required.
• All grounding contact surfaces shall be free of paint, rust, or insulation.
• Supports and hangers shall be equipotentially bonded to the cable tray.
• Cut or welded surfaces shall be re‑coated for corrosion protection.

Summary of Core Rules (Easy to Remember)

• At least 2 grounding points minimum; add one every 20–30 m for long runs.
• Galvanized trays: 2 bolts + locking to ensure conductivity.
• Painted/spray‑coated trays: 4 mm² copper jumpers + paint removal.
• Deformation joints: 16 mm² flexible jumper.
• Full continuity → safe and compliant.