Y N
Star winding with accessible neutral
An accessible-neutral star winding brings the common star point to a documented terminal.
SLD / Schematic
Symbols · NER
Neutral earthing resistor
A resistor between a transformer or generator neutral and earth that limits earth-fault current to a set value.
In plain English
What does Neutral earthing resistor mean?
A neutral earthing resistor connects the star point of a transformer or generator to earth through a defined resistance. It limits earth-fault current, typically to tens or hundreds of amperes on medium-voltage systems and a few amperes on high-resistance earthed low-voltage systems, reducing damage and arc energy while keeping enough current for protection to detect.
A simple example
Drawings show a resistor between the neutral of a star winding and the earth symbol, often with a current transformer in the neutral lead for earth-fault protection and sometimes a disconnector. The resistor current and time rating, such as 400 A for 10 seconds, are written beside it.
What the drawings help you do
The symbol does not show the resistor's monitoring, which some designs use to detect an open resistor. It also does not show whether generator and transformer neutrals are earthed at the same time, which affects fault current and circulating harmonic currents.
This particular reference
A resistor between a transformer or generator neutral and earth that limits earth-fault current to a set value. A neutral earthing resistor limits fault current resistively; an arc suppression coil compensates capacitive fault current with inductance.
- Winding
- A coil of conductor inside an electrical machine or transformer.
- Terminal
- An identified point where a conductor connects.
- Rating
- A value stating the conditions for which equipment is specified.
Read the source: Neutral grounding resistor and transformer resources · Residual current and neutral-earthing protection context
SLD / Schematic · NER
What it represents
A neutral earthing resistor connects the star point of a transformer or generator to earth through a defined resistance. It limits earth-fault current, typically to tens or hundreds of amperes on medium-voltage systems and a few amperes on high-resistance earthed low-voltage systems, reducing damage and arc energy while keeping enough current for protection to detect.
Drawings show a resistor between the neutral of a star winding and the earth symbol, often with a current transformer in the neutral lead for earth-fault protection and sometimes a disconnector. The resistor current and time rating, such as 400 A for 10 seconds, are written beside it.
The symbol does not show the resistor's monitoring, which some designs use to detect an open resistor. It also does not show whether generator and transformer neutrals are earthed at the same time, which affects fault current and circulating harmonic currents.
How to read it
- Read the current and time rating together.
- A neutral CT normally feeds earth-fault protection.
Information to show or reference
- State resistance, current and time rating.
- Show neutral CT and disconnector.
- Reference earth-fault protection settings.
A distinction that matters
A neutral earthing resistor limits fault current resistively; an arc suppression coil compensates capacitive fault current with inductance.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Neutral grounding resistor and transformer resources
Public neutral earthing resistor resource library.
Residual current and neutral-earthing protection context
Public neutral earthing and earth-fault protection context.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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