The grounding of cable tray shall meet the following requirements when the design allows the use of tray system to form grounding trunk circuit:
1. The metal cable conduit leading in or out of the metal cable tray and its support must be reliably grounded (PE) or neutral (pen), and must comply with the following specifications:
(1) The total length of the metal cable tray and its support shall be connected with the grounding (PE) or neutral (pen) main line at least two places, so that the whole tray is an electrical path.
(2) The two ends connected between non galvanized cable trays shall be bridged with copper core grounding wire, and the minimum allowable cross-sectional area of grounding wire shall not be less than 4mm2.
(3) The two ends of the connecting plate between the galvanized cable trays may not cross the grounding wire, but the two ends of the connecting plate shall not be less than 2 connecting fixing bolts with locking nuts or locking washers.
2. The connection resistance between panel and ladder end shall not be greater than 0.00033 Ω, and shall be tested by equipotential bonding tester (conductometer) or micro Ω meter. The test shall be conducted on both sides of the connection point, and the connection resistance at both ends of the whole bridge length shall not be greater than 0.5 Ω or determined by the design, otherwise, the grounding point shall be added to meet the requirements. The coating shall be removed from the grounding hole, and the special grounding washer with claw shall be used for the flat pad on one side of the bolt in contact with the coating.
3. The expansion joint or flexible joint shall be connected with braided copper wire. When another grounding main line is laid along the full length of the bridge, the tray and ladder of each section (including non-linear section) shall be reliably connected with the grounding main line at a small point; spring washer shall be installed at the connection of the grounding part to avoid loosening.