In cabling projects, common wiring methods include overhead lines, cables, steel pipes, cable trays, and busbars.

I. Grounding of Power Cables

1. For systems with 110kV and above, where the neutral point is effectively grounded, the metal sheath of single-core cables should be directly connected to the substation grounding device through a grounding switch.

2. At the terminal stations where cables transition to overhead lines in systems of 110kV and above, the metal sheath of the cable terminals should be separately grounded via a grounding switch. If not specified in the design, the grounding resistance should not exceed 4Ω. The separate grounding electrode for the cable sheath should be 3-5 meters away from the grounding electrode of the overhead lightning protection line.

3. If it is difficult to separate the grounding devices, the metal sheath of the cable terminals on overhead towers (for 110kV and above systems) should be grounded with the overhead lightning protection line through a grounding switch, with the grounding resistance not exceeding 4Ω unless otherwise specified.

4. For three-core cables below 110kV, the metal sheath at the terminals should be directly connected to the substation grounding device.

5. Grounding bolts on the casing of power cable joint boxes or intermediate junction boxes must be connected to the main grounding conductor. The metal sheath and steel armor of the cables within the box should be connected to the grounding bolts on the box casing using copper conductors equivalent to the cross-sectional area of the metal sheath.

6. When cables pass through zero-sequence current transformers, the grounding wire of the cable terminals should be grounded after passing through the zero-sequence current transformer. The metal sheath and grounding wire segment of the cable from the cable head to the point passing through the zero-sequence current transformer should be insulated from the ground.

7. When cable protection pipes are accessible, they must be grounded, either by welding to the main grounding conductor or by welding a grounding bolt to the protection pipe and connecting it to the main grounding conductor with a conductor. Inaccessible locations, such as protection pipes over 3.5 meters high or buried under roads, do not need to be grounded.

II. Grounding of Busbars

1. A busbar trunking system consists of busbars supported and insulated by materials and enclosed in a pipe or similar casing. The casing is usually made of aluminum alloy, thin steel sheets, or plastic.

2. The busbar trunking system must have grounding terminals at both the start and end, with grounding markings at these terminals. The metal casing of the busbar trunking should be connected to the PE (Protective Earth) conductor, and the contact surfaces at the connection points should preferably be galvanized for reliable grounding.

3. For aluminum alloy busbar trunking, there is no need for bridging between each section; if the casing's joint surfaces are galvanized, bridging is unnecessary. For busbar trunking with a painted casing, if the joint surfaces are not galvanized, bridging should be done using copper braided wire with a cross-sectional area of at least 16mm². Therefore, both ends of each busbar trunking section must have grounding terminals.

4. Thin steel sheet casings typically consist of four steel plates bolted together. Each bolt should have two serrated washers to pierce the insulation coating of both plates, ensuring continuity between them. Grounding bolts should be welded to the steel plate directly contacting the insulated busbars, with zinc-coated serrated lock washers. The resistance between any unpainted point on the busbar trunking and the grounding terminal should not exceed 0.1Ω.

5. The supporting frames for the busbar trunking should also be grounded. Frames that are difficult to reach may not need grounding, but the grounding of the busbar trunking casing must be reliable.

III. Grounding of Cable Trays

Cable trays include cable troughs, cable trays, and cable ladders, all of which must be grounded regardless of accessibility. In addition to connecting the cable tray's start and end to the PE conductor, interconnections between tray sections are also necessary.

1. For galvanized cable troughs, zinc is a good conductor and resistant to oxidation, and the tray's connecting plates are also galvanized, allowing direct use of the connecting plates as bridging plates. To ensure reliable bridging, each end of the connecting plate should be secured with at least two bolts with locknuts or lock washers. If the cable troughs are installed in vibrating areas, spring washers should be added to each bolt.

2. For painted or plastic-coated cable troughs, the coating is insulating, so bridging between trough sections is necessary. It is recommended to use tinned copper stranded wire with a minimum cross-sectional area of 4mm² for bridging, with tinned copper lugs crimped at both ends. Iron bolts welded at both ends of the cable troughs can rust and increase contact resistance. To avoid this, copper bolts should be welded at both ends of the cable troughs, or copper nuts should be welded to holes in the troughs for more reliable bridging.

3. The casing of plastic or fiberglass cable trays does not need grounding.

4. Copper stranded wire, galvanized flat steel, or metal components used to install supports along the cable trays can serve as the main grounding conductor. If the cable tray length is 30m or less, at least two connections to the main grounding conductor are required. If the length exceeds 30m, additional grounding points should be added every 20-30m. The start and end of the cable tray must be securely connected to the grounding network.