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Overvoltage
A function responding to voltage above its configured operating criteria.
Protection functions
Protection functions · 27
Undervoltage
A function responding to voltage below its configured operating criteria.
SLD / Schematic · 27
What it represents
An undervoltage function detects a voltage condition below its configured criteria. On an SLD, the number identifies the function rather than a particular relay product or its voltage and time settings.
On a power drawing, keep this function reference connected to the selected equipment and its complete designation. A multifunction relay can implement several numbered functions. This entry explains the reference; it supplies no settings or commissioning procedure.
How to read it
- Identify the voltage source measured by the device.
- Use the relay documentation to determine how the element is implemented and used.
Information to show or reference
- Reference the voltage inputs.
- Identify the associated relay or controller.
- Link the trip, alarm or permissive logic.
A distinction that matters
An undervoltage element and an undervoltage release are related voltage concepts but can describe different equipment and operating arrangements.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Public reference table of ANSI device-function numbers
Public manufacturer table used to check the base function-number name.
IEEE C37.2-2022: power-system device function numbers
Normative publication reference for the device-function convention.
Relion 620: functions, codes and symbols
Public examples of manufacturer-specific function names and suffixes.
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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