# Synchronism check

Canonical URL: https://eloragrid.ai/protection-functions/25-synchronism-check
Publisher: Elora Grid
Updated: 2026-10-13
Lookup label: 25
Drawing use: SLD, Schematic
Reference families: IEEE / ANSI

Checks documented synchronising conditions before a permitted connection.

## What it represents

A synchronism-check function supervises the conditions for connecting electrical sources or system sections. It is associated with the measured quantities and operating logic specified for the selected protection or control device.
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 measurement inputs used by the function.
- Read the closing-permission relationship in the documented control scheme.

## Information to show or reference

- Reference measured source or bus voltages.
- Identify the supervised closing device.
- Link the control and protection documentation.

## Important distinction

Synchronism checking is a permissive function; a generic 25 label is not a complete synchronising controller or operating sequence.

## Facts

- ANSI / IEEE function number: 25
- 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.