U RES
Residual-voltage monitoring relay
A residual-voltage relay responds to the specified residual-voltage measurement.
SLD / Schematic
Symbols · K
Earth-fault voltage relay
Relay form that operates on a voltage appearing because of an earth fault, such as between a frame and earth.
In plain English
What does Earth-fault voltage relay mean?
This relay measures a voltage that appears only when there is an earth fault, for example between exposed metalwork and a reference earth, or across a neutral earthing impedance. It is useful where earth-fault current is limited and a voltage is easier to detect than a current.
A simple example
The symbol does not say where the voltage is measured. A relay across a neutral earthing resistor and one connected between frame and auxiliary earth electrode have very different settings, so the measurement points must be drawn and labelled.
What the drawings help you do
Trace both measurement connections of the relay. Check the reference earth used by the relay. An earth-fault voltage relay measures fault-related voltage; a residual voltage relay measures zero-sequence voltage from VT windings.
This particular reference
Relay form that operates on a voltage appearing because of an earth fault, such as between a frame and earth. An earth-fault voltage relay measures fault-related voltage; a residual voltage relay measures zero-sequence voltage from VT windings.
- Coil
- A wound conductor that can produce a magnetic field when energised.
- Rating
- A value stating the conditions for which equipment is specified.
- Schematic
- A drawing showing function and connections rather than physical appearance.
Read the source: AutoCAD Electrical: Voltage monitoring relays · Residual current and neutral-earthing protection context
Schematic / SLD · K
What it represents
This relay measures a voltage that appears only when there is an earth fault, for example between exposed metalwork and a reference earth, or across a neutral earthing impedance. It is useful where earth-fault current is limited and a voltage is easier to detect than a current.
The symbol does not say where the voltage is measured. A relay across a neutral earthing resistor and one connected between frame and auxiliary earth electrode have very different settings, so the measurement points must be drawn and labelled.
How to read it
- Trace both measurement connections of the relay.
- Check the reference earth used by the relay.
Information to show or reference
- Show measurement points
- State threshold and delay
- Reference earthing arrangement
A distinction that matters
An earth-fault voltage relay measures fault-related voltage; a residual voltage relay measures zero-sequence voltage from VT windings.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
AutoCAD Electrical: Voltage monitoring relays
Public AutoCAD Electrical relay listing that names the Ground Failure Voltage Protection block; the illustration is independently drawn.
Residual current and neutral-earthing protection context
Public context for neutral-earthing and earth-fault protection.
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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