# Measured ground time-overcurrent

Canonical URL: https://eloragrid.ai/protection-functions/51x-measured-ground-time-overcurrent
Publisher: Elora Grid
Updated: 2026-10-13
Lookup label: 51X
Drawing use: SLD, Schematic
Reference families: IEEE / ANSI, Manufacturer

Applies time-overcurrent protection to a separately measured ground or neutral input in the cited Eaton family.

## What it represents

Applies time-overcurrent protection to a separately measured ground or neutral input in the cited Eaton family.
The drafting record should connect this function to the dedicated CT input and external ground/neutral sensor, then trace the measured earth-fault timing element and trip circuit. 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 dedicated CT input and external ground/neutral sensor.
- Trace the measured earth-fault timing element and trip circuit.

## Information to show or reference

- Label the dedicated CT input and external ground/neutral sensor.
- Cross-reference the measured earth-fault timing element and trip circuit.
- Retain the complete suffix, selected device tag and manufacturer manual revision.

## Important distinction

A measured ground input can have different sensitivity and CT requirements from calculated residual current.

## Facts

- Function designation: 51X
- 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.