Grounding is an essential aspect of crane safety, ensuring the protection of both personnel and equipment from electrical hazards. Proper grounding mitigates the risks of electric shock, fire, and equipment damage by providing a reliable path for electrical currents to flow safely into the earth. This guide provides a comprehensive overview of grounding requirements for cranes, including scope, structures, and resistance standards, along with detailed instructions for implementation and best practices.
Grounding Scope
Scope of Grounding:
All metal enclosures and non-current-carrying metal parts of electrical equipment on the crane must be reliably grounded.
This includes metal conduits, metal cable sheaths, and one end of the low-voltage side of safety transformers.
Grounding ensures that these components, which normally do not carry current, do not become hazardous in case of insulation failure or fault conditions.
Grounding Structure
Structural Requirements for Grounding:
Use of Metal Structures as Grounding Conductors:
The metal framework of the crane can serve as the primary grounding conductor, provided it forms a continuous and reliable electrical connection.
If there are non-welded joints within the metal structure, supplementary grounding conductors or bonding jumpers must be installed to ensure continuity.
Grounding Conductors:
Grounding connections should use flat steel with a cross-sectional area of no less than 150 mm² or copper wires with a cross-sectional area of at least 10 mm².
The connection between the grounding conductor and equipment should be achieved through welding or bolted connections.
Bolted connections must incorporate anti-loosening and anti-corrosion measures to maintain reliability over time.
Driver’s Cab Connections:
If the driver’s cab is bolted to the main crane body, electrical bonding between the two should use multi-stranded flexible copper wire with a cross-sectional area of no less than 16 mm².
Both ends of the bonding wire should be fitted with crimped terminals, fixed with galvanized bolts.
When flat steel or round steel is used for bonding, the flat steel should be no smaller than 40×4 mm, and round steel should have a diameter of no less than 12 mm.
Each bonding point should have at least two connections to ensure redundancy and reliability.
Cranes Operating on Tracks:
Cranes that operate on tracks can generally be grounded through the wheels and rails.
In cases where this is insufficient, additional dedicated grounding conductors or other effective grounding measures should be implemented.
Grounding Resistance Standards
Grounding Resistance Requirements:
Each crane rail should have at least two grounding connections to ensure adequate grounding.
Electrical bonding should be provided at rail joints to maintain continuity.
The grounding resistance at any point on the rail or crane should not exceed 4 ohms.
In cases of repeated grounding of the neutral wire, the resistance should not exceed 10 ohms.
Best Practices for Grounding Implementation
Material Selection and Installation:
Use high-quality, corrosion-resistant materials for grounding conductors and connections.
Ensure all connections are secure and regularly inspect for signs of wear, corrosion, or mechanical damage.
Apply protective coatings or covers to grounding conductors in harsh environments to extend their lifespan.
Inspection and Testing:
Perform routine testing of grounding systems to verify compliance with resistance standards.
Use specialized equipment to measure grounding resistance and identify potential faults or discontinuities.
Document all inspections and maintenance activities for future reference and compliance verification.
Conclusion
Effective grounding is a critical safety measure in crane operations. By adhering to the outlined requirements and best practices, operators can ensure the reliability and safety of their equipment. Continuous monitoring and proactive maintenance of grounding systems will further enhance operational safety and prevent electrical hazards.
