# Undervoltage

Canonical URL: https://eloragrid.ai/protection-functions/27-undervoltage
Publisher: Elora Grid
Updated: 2026-10-13
Lookup label: 27
Drawing use: SLD, Schematic
Reference families: IEEE / ANSI

A function responding to voltage below its configured operating criteria.

## 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.

## Important distinction

An undervoltage element and an undervoltage release are related voltage concepts but can describe different equipment and operating arrangements.

## Facts

- ANSI / IEEE function number: 27
- Equipment implementation: Consult the selected device manual
- Suffix interpretation: Application and manufacturer documentation

## Public references

- [Public reference table of ANSI device-function numbers](https://www.se.com/es/es/faqs/FA34639/) — Schneider Electric. Public manufacturer table used to check the base function-number name.
- [IEEE C37.2-2022: power-system device function numbers](https://ieeexplore.ieee.org/document/9984140) — IEEE. Normative publication reference for the device-function convention.
- [Relion 620: functions, codes and symbols](https://techdoc.relays.protection-control.abb/r/620-series-IEC-60870-5-103-Point-List-Manual/2.0-FP1-IEC/en-US/Functions-codes-and-symbols) — ABB. Public examples of manufacturer-specific function names and suffixes.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.