What is the value of the lightning protection grounding resistance?

The size of the grounding resistance directly reflects the good contact between the electrical device and the "ground" and also reflects the scale of the grounding network. The concept of grounding resistance is only applicable to small grounding grids; with the increase in the grounding area of ​​the grounding grid and the decrease in soil resistivity, the role of the inductive component in the grounding impedance becomes greater and greater, and large grounding grids should adopt grounding impedance design. For high-voltage and ultra-high voltage substations, the concept of "grounding impedance" should be used instead of "grounding resistance". It is recommended that the regulations adopt contact voltage and stepping voltage as safety criteria; a lightweight and accurate heterofrequency measurement system should also be used to obtain the correct results of the grounding impedance to ensure the safety of the person and equipment and facilitate the safe operation of the power system.

What is the minimum ground resistance considered safe?

The smaller the grounding resistance, the better.

Different equipment requirements are different:

1. In a direct grounding system with a neutral point below 1kV, the grounding resistance is less than or equal to 4Ω, and the repeated grounding resistance is less than or equal to 10Ω;

2. In a neutral point with a voltage below 1kV, the grounding resistance is generally stipulated to be 4Ω. Therefore, according to actual installation experience, the grounding resistance in the street lamp lighting system should be less than or equal to 4Ω. Single-point grounding is usually used to test the grounding resistance with the following types of instruments;

3. Working grounding (zero protection), protective grounding: In a 380/220V low-voltage system, the grounding current is very small, generally not more than a few amperes, so the specified connection resistance is not greater than 4Ω. When the capacity is below 100kV Amp, the grounding resistance can also be relaxed to not greater than 10Ω.

4. Repeated grounding: According to relevant regulations, in a low-voltage grid with direct grounding of neutral points, the neutral line should be repeatedly grounded at the terminals and branch lines of the overhead line and at each kilometer along the line, and each repeated grounding resistance should not be greater than 10Ω; in the case where the working grounding resistance is allowed to be 10Ω, each repeated grounding resistance should be no more than 30Ω, but the repeated grounding shall not be less than 3.