# Reverse-current measuring relay

Canonical URL: https://eloragrid.ai/symbols/reverse-current-relay
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: K
Drawing use: Schematic, SLD
Reference families: IEC, Manufacturer

Measuring relay that operates when current flows in the opposite direction to normal, such as back-feed into a DC source.

## In plain English

### What does Reverse-current measuring relay mean?

A reverse-current relay compares the direction of current with a reference and operates when current flows the wrong way. Classic uses are DC generators and battery chargers in parallel, where a failed source would otherwise draw current from the bus, and rectifier feeders where back-feed indicates a fault.

### A simple example

On the schematic the relay box carries a current quantity with a direction additional drawing mark, and its contacts are drawn elsewhere in the trip or alarm circuit. The box does not show the pick-up level or time delay, and in AC systems the equivalent requirement is usually met with a directional power function rather than a simple current-direction element.

### What the drawings help you do

Identify which direction is treated as normal for the source. Find the contacts that trip or disconnect the source. A reverse-current relay responds to current direction; a maximum-current relay responds to magnitude regardless of direction.

### This particular reference

Measuring relay that operates when current flows in the opposite direction to normal, such as back-feed into a DC source. A reverse-current relay responds to current direction; a maximum-current relay responds to magnitude regardless of direction.

### Terms

- DC: Direct current: electricity flowing in one direction.
- AC: Alternating current: electricity whose direction changes periodically.
- Normally open / normally closed: The contact state in the normal condition defined for the drawing.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [AutoCAD Electrical: Current monitoring relays](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-E0DDA638-4664-4F1E-B191-29A4C40C4A0A.htm)
- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/)


## What it represents

A reverse-current relay compares the direction of current with a reference and operates when current flows the wrong way. Classic uses are DC generators and battery chargers in parallel, where a failed source would otherwise draw current from the bus, and rectifier feeders where back-feed indicates a fault.
On the schematic the relay box carries a current quantity with a direction qualifier, and its contacts are drawn elsewhere in the trip or alarm circuit. The box does not show the pick-up level or time delay, and in AC systems the equivalent requirement is usually met with a directional power function rather than a simple current-direction element.

## How to read it

- Identify which direction is treated as normal for the source.
- Find the contacts that trip or disconnect the source.

## Information to show or reference

- State normal current direction
- Give pick-up and delay
- Reference the trip contact

## Important distinction

A reverse-current relay responds to current direction; a maximum-current relay responds to magnitude regardless of direction.

## Facts

- Measured quantity: Current direction relative to normal flow
- Publisher reference token: HCR1F28 (Autodesk identifier; not an IEC database ID)
- Preview: Independent educational concept; consult the publisher and applicable standard for the exact graphic

## Public references

- [AutoCAD Electrical: Current monitoring relays](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-E0DDA638-4664-4F1E-B191-29A4C40C4A0A.htm) — Autodesk. Public AutoCAD Electrical relay listing that names the Come Back Current Protection block; the illustration is independently drawn.
- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/) — IEC. IEC context for graphical symbols used in diagrams; no IEC graphic is reproduced.

## 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.