Neutral Earthing Resistor

Neutral grounding resistor (NGR) is another name for a neutral earthing resistor. ‘Earthing’ and ‘grounding’ describe the same function in this context; the terminology varies by region and project specification.

A quotation needs the electrical system details, required operating duty and installation conditions. Providing these together helps the manufacturer select and size the resistor for the application.

Provide the system line-to-line voltage and the required maximum earth fault current.

The resistor is designed for the phase-to-neutral voltage rather than the line-to-line voltage.

The selected current must satisfy both equipment protection requirements and protection relay coordination.

The required resistance is determined from the phase-to-neutral voltage and the desired earth fault current. Include any resistance value specified by the project so it can be checked against these requirements.

Specify how long the resistor must carry the stated earth fault current before protection clears the fault. The required duration should come from the project’s protection design, rather than an assumed standard rating.

If the resistor must carry current continuously, state the continuous current requirement separately. Continuous duty affects resistor sizing and material selection and must be considered at the quotation stage.

Identify the installation environment and any project-specific enclosure requirements:

IP23 is a common ingress protection (IP) rating for neutral earthing resistor enclosures. Other available IP ratings are IP00, IP33, IP43 and IP54. Commonly specified enclosure materials are 2 mm 304 stainless steel (304SS), 316 stainless steel (316SS) or mild steel. Provide the required IP rating, corrosion exposure and any specified enclosure material, thickness or finish with your quotation request. Confirm these choices are suitable for the application.

Include the preferred enclosure colour or project colour reference with the request for quotation.

Typical ambient design temperatures specified for Australian installations are 45°C to 50°C. State the site’s specified ambient temperature range; do not substitute these typical values for the actual project requirement.

For outdoor installations, indicate whether the enclosure will be exposed to direct sunlight and whether the project calls for a sunshield. Solar exposure can increase enclosure temperatures and should be considered alongside the ambient conditions.

Include the following information in your request for quotation (RFQ):

Contact Backer Cynebar Ohmic with your project requirements for neutral earthing resistor selection and quotation assistance. If a requirement is not yet known, identify it as needing confirmation rather than supplying an assumed value.