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What is Neutral Grounding Resistor

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Neutral Grounding Resistors (NGRs) form an essential part of electrical power systems, providing a crucial connection between the neutral point of transformers and the grounding system. Understanding their purpose, sizing considerations, and applications is vital for ensuring the safety and efficient operation of power distribution networks.

Let’s embark on a comprehensive exploration of Neutral Grounding Resistors to illuminate their role in electrical infrastructure.

What is a Neutral Grounding Resistor?

A Neutral Grounding Resistor is a specialized resistor installed between the neutral point of transformers and the ground. It limits the fault current in the event of an insulation breakdown or fault, effectively mitigating potential damage and ensuring the stability of the power distribution system.

Why Neutral Grounding Resistors are Used

Fault Current Limitation:

  • Neutral Grounding Resistors restrict fault currents that may occur due to line-to-ground faults, protecting transformers and other equipment from damage caused by excessive fault currents.

Voltage Stabilization:

  • By grounding the neutral point through a resistor, the system’s transient voltages and inrush currents can be controlled, thereby minimizing the risk of overvoltages and ensuring stable operation.

System Reliability:

  • Utilizing NGRs enhances the overall reliability of power systems by preventing prolonged ground faults, reducing harmonics, and limiting transient disturbances.

How to Size Neutral Grounding Resistors

Calculating Fault Currents:

  • Determining the maximum fault current that the NGR will experience is crucial for sizing it appropriately. This involves analyzing potential fault scenarios and considering factors such as system configuration and fault clearing times.

Thermal Considerations:

  • Sizing NGRs also involves accounting for the thermal capacity of the resistor to ensure it can handle the fault current without overheating. Factors such as ambient temperature and duty cycles play a pivotal role in this assessment.

Resistor Material and Construction:

  • The material composition and construction of the NGR, such as wirewound or grid resistors, are significant factors that influence their sizing and performance characteristics.

    Application of Neutral Grounding Resistors

    Power Transformers:

    • NGRs are commonly employed with power transformers to control transient overvoltages and limit fault currents, safeguarding the transformer and associated equipment.

    Generator Systems:

    • In generator applications, NGRs contribute to controlling potential ground fault currents, ensuring the stability and reliability of the generator system.

    Industrial and Utility Networks:

    • Neutral Grounding Resistors are integral components in industrial and utility power distribution networks, playing a vital role in protecting equipment and personnel while promoting system stability.


      Neutral Grounding Resistors are indispensable elements of electrical power systems, serving as crucial safety and stability assets that mitigate fault currents and transient disturbances. Their careful sizing, strategic installation, and reliable performance are foundational to maintaining the operational integrity of power networks across various industrial and utility settings.

      By comprehending the role and significance of NGRs, engineers and maintenance personnel can effectively integrate these components into power infrastructure, bolstering the resilience and safety of electrical systems. Embrace the illuminating capabilities of Neutral Grounding Resistors, and fortify the foundation of power distribution systems with enhanced safety and operational excellence.

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