# Voltage-dependent overcurrent

Canonical URL: https://eloragrid.ai/protection-functions/51v-voltage-dependent-overcurrent
Publisher: Elora Grid
Updated: 2026-10-13
Lookup label: 51V
Drawing use: SLD, Schematic
Reference families: IEEE / ANSI, Manufacturer

Changes overcurrent operation according to the measured voltage using the relay's documented voltage-dependent method.

## What it represents

Changes overcurrent operation according to the measured voltage using the relay's documented voltage-dependent method.
The drafting record should connect this function to the current inputs, VT circuit and selected voltage-dependence mode, then trace the overcurrent trip logic and voltage-supervision reference. Keep the complete designation and equipment tag together so that the SLD, relay logic and terminal schedule describe the same implementation.
The cited mapping is a public manufacturer example (Eaton ETR family). Suffixes are not universal equivalences across products, and this reference supplies neither a protection setting nor certification of the selected scheme.

## How to read it

- Identify the current inputs, VT circuit and selected voltage-dependence mode.
- Trace the overcurrent trip logic and voltage-supervision reference.

## Information to show or reference

- Label the current inputs, VT circuit and selected voltage-dependence mode.
- Cross-reference the overcurrent trip logic and voltage-supervision reference.
- Retain the complete suffix, selected device tag and manufacturer manual revision.

## Important distinction

Voltage restraint and voltage control are distinct implementations; a 51V label must be accompanied by the selected device's mode.

## Facts

- Function designation: 51V
- Base function: 51 — Time overcurrent
- Published mapping: Eaton ETR family
- Suffix scope: Application or manufacturer specific; check the complete drawing legend and selected device manual.

## Public references

- [ETR-4000 and ETR-5000 transformer protection function tables](https://www.eaton.com/us/en-us/catalog/electrical-circuit-protection/transformer-relays.html) — Eaton. Public primary-source function or application mapping used to identify this designation; wording and drafting notes are original.
- [IEEE C37.2-2022: power-system device function numbers](https://ieeexplore.ieee.org/document/9984140) — IEEE. Device-number and suffix convention. This page is not a reproduction of the full licensed standard.

## 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.