Causes Of Grounding Failure in Distribution Box

Grounding failure in a distribution box is a serious safety hazard, potentially leading to live equipment casing, electric shock, or equipment damage. Common causes include:

1. Grounding Wire Connection Problems
Loose or detached joints: Vibration, thermal expansion and contraction, or initial improper installation can cause grounding terminals or bolts to loosen.
Cable breakage: Grounding wires may break due to mechanical damage, overcurrent burnout, or aging.
Poor contact: Paint, rust, or oxide layers at connections can cause excessive contact resistance, rendering the connection ineffective.
Incorrect or missing connections: Grounding wires may not have been connected correctly during construction, or critical jumper wires, such as those between the door and the box, may have been omitted.
Corrosion at connection points: In humid or polluted environments, connection points are prone to oxidation, forming an oxide film on the metal surface, resulting in high resistance or an open circuit.

2. Grounding electrode and grounding trunk line faults
Grounding electrode corrosion: Buried galvanized angle steel, steel pipes, and other grounding electrodes may break or have significantly reduced cross-sections due to long-term soil corrosion, especially in acidic, alkaline, or damp soils.

Damage to the grounding main line: The main line connecting the distribution box and the grounding electrode is severed during construction, damaged by vehicles, or intentionally removed.

Sudden changes in soil resistivity: Prolonged drought, frozen ground, or changes in groundwater levels may cause a sudden and significant increase in grounding resistance, exceeding the allowable value.

3. System Factors

Incorrect Wiring: Operational errors such as reversing the live, neutral, and ground wires cause the equipment casing to become energized.

Failure of Equipotential Bonding: The conductor used for equipotential bonding breaks, disrupting the reference potential of the entire grounding system.

Lightning Overvoltage Damage: Powerful lightning currents or operational overvoltages may melt or carbonize weak points in the grounding lines.

Damage During Modification and Repair: During later construction or renovation, workers unfamiliar with electrical wiring may unintentionally cut the grounding wire or alter the grounding path.

4. Design and Material Defects

Insufficient Grounding Wire Cross-Section: The selected grounding wire is too thin and cannot withstand the expected fault current, burning out after long-term operation or a single short circuit.

Insufficient Grounding Electrode Burial Depth: The designed depth is not reached, making it highly susceptible to the effects of surface soil moisture and freeze-thaw cycles, resulting in unstable grounding resistance.

Substandard Materials: Using inferior steel with a thin or no galvanized layer will quickly corrode and fail.

Non-Standardized Workmanship: Rough installation or poor welding quality, such as weak welding of the grounding flat steel, resulting in insufficient contact surface.

5. Environmental Factors

Humidity and Moisture: Indoor installation or excessively low conduit openings can cause cables to become damp, reducing insulation resistance and leading to leakage.

Chemical Corrosion: Acidic or alkaline soils or high-salt spray environments in industrial settings can severely damage grounding devices, causing them to break.

External Damage: This includes animal bites, soil subsidence, or construction drilling.