Problem description:
I just arrived at the construction unit, and the project is a 33-story residential building. Its grounding device is led from the pile to the earth. I wonder if there are any other grounding devices besides this way? Please make a list, preferably with a picture! thank you
Analysis:
1. There are two requirements for installing grounding device:
(1) The grounding resistance of the grounding device must be less than 4 ohms.
(2) Generally, there should be no less than two grounding electrodes.
2. There are two types of grounding devices:
(1) Natural grounding On the premise that the grounding resistance can be less than 4 ohms, in order to save materials and reduce workload, natural grounding can be given priority. Natural grounding is the use of underground water supply, drainage or other metal pipes (excluding flammable liquids, flammable and explosive gases and metal pipes wrapped with insulating substances), cables with metal sheaths, metal well pipes, metal structures of buildings and foundations of reinforced concrete buildings as natural grounding bodies.
(2) Artificial grounding generally uses steel bars as grounding electrodes, and the length is more than 2.2m.. After digging a pit with a depth of 1 m, drive it vertically into the bottom of the pit, with a buried depth of not less than 2m (3m from the ground).
When the soil resistivity is high or the buried depth is not enough, a long-acting resistance reducer should be placed around the grounding electrode.
Grounding wire generally adopts bare wire (including flat steel and round steel) or insulated wire (copper core or aluminum core). It is not recommended to use aluminum core wire. When connecting the grounding wire, there should be no broken marks or joints in the wires used to prevent the mechanical strength from decreasing and the resistance from increasing. It is forbidden to use aluminum conductor in the underground part of grounding wire. The connection between grounding wire and grounding electrode generally adopts reliable connection methods such as welding or crimping.
The grounding devices of newly-built houses shall be designed and constructed according to the above requirements and methods, and the grounding devices that meet the above requirements and methods shall be regarded as qualified. Therefore, reasonable and safe grounding devices should be designed before the construction of residential buildings to ensure the safety of future residents.
The grounding device shall be inspected regularly as required, at least once a year, and the grounding resistance shall be tested by the "grounding resistance tester". When testing with a multimeter, it is necessary to install two temporary grounding electrodes B and C about 3m away from the grounding electrode A (as shown in the figure):
3m 3m
|←—→|←—→|
C A B
If Rab = Ra+Rb = 8 ohms, RAC = Ra+RC = 6 ohms and RBC = Rb+RC = 10 ohms are measured, then Ra = 2 ohms can be calculated, which is the grounding resistance of the grounding device.
For old residential buildings, artificial grounding should generally be adopted. If there is natural grounding, before welding or reliable pressure welding, rust removal and cleaning should be carried out on the objects selected as natural grounding electrodes.