# Minimum-voltage measuring relay

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

Measuring relay that operates when voltage falls below a set level while some voltage is still present.

## In plain English

### What does Minimum-voltage measuring relay mean?

The minimum-voltage relay form operates when the measured voltage falls below its setting. It is used for motor undervoltage tripping, load shedding and transfer schemes, where a sustained voltage dip indicates a supply problem rather than a momentary disturbance.

### A simple example

The symbol shows the voltage quantity and the less-than threshold but not the time delay, which phases are monitored or whether operation is blocked on VT fuse failure. Without a blocking input a blown VT fuse can cause an unwanted trip, so the supervision arrangement should be cross-referenced.

### What the drawings help you do

Check which phase voltages are monitored. Look for VT supervision or fuse-failure blocking. A minimum-voltage relay responds to a reduced voltage; a loss-of-voltage relay responds to absence of voltage.

### This particular reference

Measuring relay that operates when voltage falls below a set level while some voltage is still present. A minimum-voltage relay responds to a reduced voltage; a loss-of-voltage relay responds to absence of voltage.

### Terms

- Coil: A wound conductor that can produce a magnetic field when energised.
- Phase: One of the related AC waveforms in a power system.
- Signal: Electrical information passed between devices, rather than necessarily the main power supply.

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: Voltage monitoring relays](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-5296749E-9336-4B07-9956-160963D6C848.htm)
- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/)


## What it represents

The minimum-voltage relay form operates when the measured voltage falls below its setting. It is used for motor undervoltage tripping, load shedding and transfer schemes, where a sustained voltage dip indicates a supply problem rather than a momentary disturbance.
The symbol shows the voltage quantity and the less-than threshold but not the time delay, which phases are monitored or whether operation is blocked on VT fuse failure. Without a blocking input a blown VT fuse can cause an unwanted trip, so the supervision arrangement should be cross-referenced.

## How to read it

- Check which phase voltages are monitored.
- Look for VT supervision or fuse-failure blocking.

## Information to show or reference

- State threshold and delay
- Show VT source
- Reference blocking input

## Important distinction

A minimum-voltage relay responds to a reduced voltage; a loss-of-voltage relay responds to absence of voltage.

## Facts

- Measured quantity: Voltage below a set level
- Publisher reference token: HCR1F35 (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: Voltage monitoring relays](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-5296749E-9336-4B07-9956-160963D6C848.htm) — Autodesk. Public AutoCAD Electrical relay listing that names the Minimum Voltage 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.