# Phase-sequence indicator

Canonical URL: https://eloragrid.ai/symbols/phase-sequence-indicator
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: PSI
Drawing use: Schematic
Reference families: IEC, Manufacturer

Instrument that shows whether three-phase supply rotation is positive or reversed before motors are run or sources paralleled.

## In plain English

### What does Phase-sequence indicator mean?

A phase-sequence indicator connects to all three phases and shows whether rotation is L1-L2-L3 or reversed. It is used when commissioning motors, generators and supply changes, because wrong rotation reverses motors and prevents correct paralleling.

### A simple example

The instrument gives a check at one moment and does not protect anything on its own. If permanent protection against reversed rotation is needed, a phase-sequence monitoring relay with contacts must be shown instead of, or as well as, the indicator.

### What the drawings help you do

Confirm all three phases are connected in the stated order. Check whether a protective relay is also required. A phase-sequence indicator only displays rotation; a phase monitoring relay acts on incorrect rotation or loss of phase.

### This particular reference

Instrument that shows whether three-phase supply rotation is positive or reversed before motors are run or sources paralleled. A phase-sequence indicator only displays rotation; a phase monitoring relay acts on incorrect rotation or loss of phase.

### Terms

- Normally open / normally closed: The contact state in the normal condition defined for the drawing.
- Coil: A wound conductor that can produce a magnetic field when energised.
- Phase: One of the related AC waveforms in a power system.

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.

- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/)


## What it represents

A phase-sequence indicator connects to all three phases and shows whether rotation is L1-L2-L3 or reversed. It is used when commissioning motors, generators and supply changes, because wrong rotation reverses motors and prevents correct paralleling.
The instrument gives a check at one moment and does not protect anything on its own. If permanent protection against reversed rotation is needed, a phase-sequence monitoring relay with contacts must be shown instead of, or as well as, the indicator.

## How to read it

- Confirm all three phases are connected in the stated order.
- Check whether a protective relay is also required.

## Information to show or reference

- Show phase connections
- State expected rotation
- Reference commissioning check

## Important distinction

A phase-sequence indicator only displays rotation; a phase monitoring relay acts on incorrect rotation or loss of phase.

## Facts

- Inputs: Three phase voltages
- Output: Display only
- Preview: Independent educational concept; consult the applicable standard and project legend for the exact graphic

## Public references

- [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.