# Neutral-unbalance relay between two polyphase systems

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

Relay form measuring current in a link joining the star points of two polyphase systems, such as split capacitor banks.

## In plain English

### What does Neutral-unbalance relay between two polyphase systems mean?

This form shows a current relay in the conductor that joins the neutral points of two star-connected polyphase systems. A familiar application is the double-star capacitor bank, where a CT in the link between the two star points detects unbalance caused by failed capacitor units.

### A simple example

In a healthy balanced arrangement the link carries little current, so the relay setting is a small fraction of phase current and must allow for natural unbalance. The symbol does not tell you the alarm and trip stages or the compensation for inherent unbalance; those are in the bank protection settings.

### What the drawings help you do

Identify the two star points joined by the measured link. Look for separate alarm and trip stages. This relay measures the link between two star points; a neutral-current relay measures one neutral path to earth or to the supply.

### This particular reference

Relay form measuring current in a link joining the star points of two polyphase systems, such as split capacitor banks. This relay measures the link between two star points; a neutral-current relay measures one neutral path to earth or to the supply.

### Terms

- Coil: A wound conductor that can produce a magnetic field when energised.
- Phase: One of the related AC waveforms in a power system.
- Rating: A value stating the conditions for which equipment is specified.

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

This form shows a current relay in the conductor that joins the neutral points of two star-connected polyphase systems. A familiar application is the double-star capacitor bank, where a CT in the link between the two star points detects unbalance caused by failed capacitor units.
In a healthy balanced arrangement the link carries little current, so the relay setting is a small fraction of phase current and must allow for natural unbalance. The symbol does not tell you the alarm and trip stages or the compensation for inherent unbalance; those are in the bank protection settings.

## How to read it

- Identify the two star points joined by the measured link.
- Look for separate alarm and trip stages.

## Information to show or reference

- Show the interconnecting link and CT
- State alarm and trip settings
- Note inherent unbalance compensation

## Important distinction

This relay measures the link between two star points; a neutral-current relay measures one neutral path to earth or to the supply.

## Facts

- Measured quantity: Current in a neutral interconnection between two systems
- Publisher reference token: HCR1F33 (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 In Neutral between 2 Multi-Phase Systems 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.