Specification for Grounding Wires of Container Houses

The specification for grounding wires of container houses must strictly adhere to national standards, with core requirements covering grounding resistance, materials, construction, and inspection and maintenance, as detailed below:

I. Core Regulatory Bases

1. GB 50057-2010 'Design Code for Protection of Structures against Lightning'
   • Specifies the lightning protection grounding resistance values for container houses: Class I lightning protection buildings ≤10Ω, Class II ≤30Ω, and ordinary container houses (Class III) ≤10Ω; if located in high-risk areas (such as open spaces), the lightning protection grounding resistance must be ≤4Ω.
   • Material requirements for grounding electrodes: galvanized flat steel (40mm×4mm) or round steel (diameter ≥8mm), with a burial depth of ≥0.6 meters.
2. GB 50169-2016 'Code for Construction and Acceptance of Grounding Connection for Electric Device Installation Engineering'
   • Specifies the connection methods for grounding wires: welding requires three-sided welding, and bolt connections require spring washers to prevent loosening; anti-corrosion treatment involves hot-dip galvanizing or applying asphalt; and testing requires the use of a grounding resistance tester.
3. JGJ 46-2005 'Technical Code for Safety of Temporary Electrification on Construction Site'
   • Emphasizes that temporary buildings (such as container houses on construction sites) must adopt the TN-S system (three-phase five-wire system), with the working neutral wire (N) strictly separated from the protective neutral wire (PE).

II. Types of Grounding and Construction Points

1. Protective Grounding
   • To prevent electric shock from equipment leakage, the metal shell of the container house must be grounded. The cross-sectional area of the grounding wire must be ≥1/2 of the cross-sectional area of the phase wire (copper wire ≥2.5mm²), and the connection points must be treated to prevent loosening.
2. Lightning Protection Grounding
   • In open areas, lightning rods (height ≥4 meters) must be installed, with down conductors connected to independent grounding electrodes. The grounding resistance must be divided according to the lightning protection level, with high-risk areas requiring ≤4Ω.
3. Iterative Grounding
   • Mobile buildings (including container houses) must be equipped with iterative grounding, with a resistance of ≤10Ω in dry environments and ≤4Ω in humid environments, forming redundant protection through multiple connections.

III. Materials and Construction Process

1. Materials for Grounding Electrodes
   • Priority is given to galvanized steel pipes (diameter ≥48mm) or angle steels (50mm×50mm×5mm), with a length of ≥2.5 meters; for connecting wires, it is recommended to use multi-strand copper core wires with a cross-sectional area of ≥16mm².
2. Construction Steps
   • Bury vertical grounding electrodes (spacing ≥5 meters, top ≥0.8 meters above the ground);
   • Use flat steel to horizontally connect the grounding electrodes to form a closed loop, with anti-corrosion treatment at the welding points;
   • Connect the metal frame of the container house to the grounding system at multiple points.

IV. Inspection and Maintenance

1. Regular Inspection
   • Inspect the grounding resistance value before the thunderstorm season each year, and add resistance reducers or increase grounding electrodes if the value exceeds the standard.
2. Daily Inspection
   • Inspect the connection points for rust and bolt loosening every six months; testing should be conducted in dry weather using professional instruments (such as the ZC-8 type or Fluke 1625).

Case Warning: A construction site experienced an electric shock accident due to the lack of iterative grounding, causing the metal shell of the container house to become electrified after a lightning strike. The original grounding resistance was as high as 50Ω, but after rectification, it was reduced to 3.8Ω, meeting safety standards.