By hvhipot 
Metal enclosures for transformers, switchgear, and transformers (PT, CP), distribution cabinets, control and protection panels, metal frames, lightning protection equipment, cable heads, and metal barriers. The grounding device has the following requirements:
① The indoor angle steel foundation and bracket should be connected to a flat steel with a cross-sectional area of not less than 25 × 4mm2 as the grounding main line, and then led out to the outdoor area and connected to the outdoor grounding device;
② The grounding body should be at least three meters away from the wall of the substation, with a length of 2.5 meters. The distance between two grounding bodies should be 5 meters;
③ The preferred form of grounding network is a closed loop type. If the grounding resistance cannot meet the requirements, an external grounding body can be added;
④ The grounding resistance of the entire grounding grid should not exceed 4 ohms.