How to ensure that the charger of an electric vehicle is well grounded

Ensuring that the charger of an electric vehicle is well grounded is a key measure to guarantee charging safety, prevent electric shock and equipment damage. The following systematically elaborates on how to achieve reliable grounding from the four aspects of grounding system design, installation, detection and maintenance, combined with specific methods and standards:

First, design requirements for the grounding system

Grounding resistance standard

According to the standards of the International Electrotechnical Commission (IEC), the grounding resistance of the charger should be ≤4Ω (in some high-risk scenarios, it should be ≤1Ω). The lower the grounding resistance is, the easier it is for the current to pass through the ground wire and enter the ground when there is a leakage, reducing the risk of electric shock.

Example: If the leakage current of the charger is 30A and the grounding resistance is 4Ω, the human contact voltage is 120V (dangerous). If the resistance drops to 1Ω and the voltage drops to 30V (within the safety threshold).

Selection of grounding materials

Conductor material: Copper or hot-dip galvanized steel should be given priority, and aluminum, which is prone to corrosion, should be avoided.

Cross-sectional area requirement: The cross-sectional area of the grounding wire should be ≥16mm² (for copper wire) or ≥25mm² (for aluminum wire) to carry the fault current.

Connection method: Welding or crimping process is adopted to ensure that the contact resistance is ≤0.1Ω.

Grounding electrode configuration

Vertical grounding electrode: Length ≥2.5m, diameter ≥16mm, burial depth ≥0.8m.

Horizontal grounding grid: It is a circular network composed of multiple grounding electrodes, with a spacing of ≥5m, to reduce grounding resistance.

Second, installation and construction standards

The grounding electrode is buried

Avoid underground pipelines, cables and other facilities. The burial depth should exceed the permafrost layer (≥1m in northern regions).

Backfill soil should be compacted in layers to prevent loose soil from causing an increase in grounding resistance.

Grounding wire connection

The charger casing is connected to the grounding electrode through an independent ground wire. It is strictly prohibited to share it with the neutral wire (N wire).

The connection points need to be treated for anti-corrosion (such as applying conductive paste or installing anti-rust boxes).

Equipotential bonding

Reliably connect the metal casing of the charging pile, nearby metal components (such as railings) to the grounding system to eliminate the potential difference.

Third, methods for grounding quality inspection

Grounding resistance test

Tools: Use a ground resistance tester (such as a clamp meter, ZC-8 type megohmmeter).

Step:

Disconnect the power supply of the charger.

Connect the P and C terminals of the tester to the auxiliary electrodes and the E terminal to the grounding electrode.

Read the resistance value. If it is greater than 4Ω, the cause needs to be investigated (such as corrosion of the grounding electrode or loose connection).

Frequency: Test immediately after new installation, and retest before the thunderstorm season every year thereafter.

Contact voltage test

Simulate a leakage scenario and measure the voltage difference between the charger casing and the ground. It should be ≤50V (the safe voltage threshold).

Insulation resistance test

The insulation resistance between the power cord and the ground wire of the charger should be measured with a megohmmeter, which should be ≥1MΩ (≥0.5MΩ in a humid environment).

Fourth, maintenance and fault handling

Regular inspection

Check the appearance of the grounding wire (free from damage and rust) and the tightness of the connection points every month.

The grounding resistance is detected annually, the data is recorded and a trend chart is drawn.

Common Fault Handling

Increase in grounding resistance

Reasons: Corrosion of the grounding electrode, dry soil, loose connection.

Treatment: Replace the grounding electrode, water to moisten the soil, and tighten the connection points.

Grounding wire breakage

Reasons: Mechanical damage, aging.

Treatment: Replace the grounding wire of the same specification and carry out anti-corrosion treatment again.

Emergency measures

If a grounding failure is detected, immediately stop using the charger and hang a "Do Not Close" warning sign until the repair is completed and the re-test is passed.

Fifth, key points to note

No unauthorized modification: Users are not allowed to change the grounding system without authorization. It must be operated by a professional electrician.

Thunderstorm weather protection: Lightning strikes may damage the grounding system. After a thunderstorm, it is necessary to prioritize checking the grounding resistance.

Compliance verification: Ensure that the charger and grounding system comply with standards such as GB/T 18487.1-2015 and IEC 61851.

Through the closed-loop management of the above design, installation, inspection and maintenance, it can effectively ensure that the electric vehicle charger is well grounded and reduce the risk of electric shock to an acceptable level. It is recommended that users establish a grounding system file to record each detection data and maintenance situation, providing a basis for long-term safe operation.