What should the grounding resistance be in Ohms? Limit Values.
Short answer: What should the grounding resistance be in ohms? It is not a single constant value; This varies depending on the system type (TT, TN), the protective device, and the purpose of the installation. Generally accepted references: for lightning protection (lightning rod) grounding. ≤ 10 ohm, In systems protected by residual current devices (RCDs), this value ensures that the touch voltage remains below 50 V.
“"What should my grounding resistance be in ohms?" is one of the most frequently asked, yet most misunderstood, questions. There's no single magic number; the value depends on the type of installation and the type of protection it provides.
Reference Values According to System and Purpose
| APPLICATION | Common target value |
|---|---|
| Lightning protection (lightning rod) | ≤ 10 ohm |
| RCD system (TT) | RA According to the rule × IΔn ≤ 50 V |
| Plant/system grounding | According to regulations and design |
| Sensitive electronics / data center | Usually much lower (≤ 1-2 ohms) |
RCD Rule: 50V Limit
In grounding systems protected by residual current devices (RCDs), the basic rule is: grounding resistance (RAThe product of the voltage (V) and the relay's rated leakage current (IΔn) must remain below the allowable touch voltage (usually 50 V). That is to say... RA × IΔn ≤ 50 V. While this theoretically allows for high resistance with a low leakage current (e.g., 30 mA) relay, in practice much lower values are targeted for safety and continuity.
Why Isn't There a Single Value?
Because the function of grounding varies depending on the system: discharging lightning, carrying fault current to the relay, or filtering noise are different requirements. The exact target value is...; Regulations on Grounding in Electrical Installations And within the framework of relevant standards, it is determined according to the design of the installation. Therefore, correctly interpreting the measurement result is as important as taking the measurement itself.
For accurate measurement and for the results to be interpreted and reported in accordance with regulations. periodic inspection of grounding system You can benefit from our service.
Frequently Asked Questions
My reading came back high, what should I do?
The number/depth of grounding electrodes can be increased, connections and corrosion can be checked, or soil improvement solutions can be applied; measurement and evaluation determine the correct action.
For accredited grounding measurements. Our Grounding Systems Services Examine it.