# Undervoltage-release holding interface

Canonical URL: https://eloragrid.ai/symbols/undervoltage-release-holding-interface
Publisher: Elora Grid
Updated: 2026-11-03
Lookup label: UHI
Drawing use: Schematic
Reference families: Manufacturer

Representation: Functional block
Installation focus: switchgear
Input: Release control voltage
Output: Release holding state

Identifies the control-energy condition that holds the documented undervoltage release in its normal state.

## In plain English

### What this block does

Identifies the control-energy condition that holds the documented undervoltage release in its normal state.

### A simple example

In a medium-voltage switchgear drawing, the operating reference helps the reader distinguish the interrupting device from its isolation, earthing and auxiliary-control interfaces. For this reference, the drawing identifies “Release control voltage” at the input and “Release holding state” at the output. Its operation differs from an energized shunt-trip command.

### What the drawings help you do

Start at the named input: Release control voltage. Identify its source device or document and the state represented on the drawing. Follow the named output: Release holding state. Cross-reference its destination and separate the command from confirmation that the equipment responded.

### Terms

- Input: Release control voltage
- Output: Release holding state
- Application reference: An explanation of a named drawing function or circuit relationship; the project documents define the equipment and its connections.

Concept diagram: Release control voltage → UHI → Release holding state
A reading guide. The entry's original illustration and input/output facts describe this application.

- [High-voltage circuit breakers](https://www.siemens-energy.com/global/en/home/products-services/product-offerings/circuit-breakers.html)


## What it represents

Identifies the control-energy condition that holds the documented undervoltage release in its normal state. A switching-device operating reference adds the specific mechanism or duty context needed to interpret its place in a power circuit. The same basic switching outline can serve different equipment constructions, so the added description must remain attached to its device tag.
In a medium-voltage switchgear drawing, the operating reference helps the reader distinguish the interrupting device from its isolation, earthing and auxiliary-control interfaces. For this reference, the drawing identifies “Release control voltage” at the input and “Release holding state” at the output. Its operation differs from an energized shunt-trip command.
Use the device schedule for its actual construction, operating duty and ratings. These original functional illustrations describe the named role and do not certify a standard glyph or product footprint. The functional block is an independent explanation of this named application. Equipment-specific ratings, terminal connections and operating conditions must be established in the project documentation.

## How to read it

- Start at the named input: Release control voltage. Identify its source device or document and the state represented on the drawing.
- Follow the named output: Release holding state. Cross-reference its destination and separate the command from confirmation that the equipment responded.
- Its operation differs from an energized shunt-trip command.
- Use the device schedule for its actual construction, operating duty and ratings. These original functional illustrations describe the named role and do not certify a standard glyph or product footprint.

## Information to show or reference

- Label the source and connection reference for release control voltage.
- Identify the destination and defined state of release holding state.
- Record the equipment or control-document revision supporting this functional block.
- Check this application limit in the project design: Its operation differs from an energized shunt-trip command.

## Important distinction

Its operation differs from an energized shunt-trip command. This reference describes the named application; it does not establish a new IEC graphical symbol, an ANSI device-function number or an exact manufacturer connection diagram.

## Facts

- Representation: Functional block
- Installation focus: Switchgear
- Input / boundary: Release control voltage
- Output / connection: Release holding state
- Lookup label: UHI is a library lookup label, not a standard device designation.

## Public references

- [High-voltage circuit breakers](https://www.siemens-energy.com/global/en/home/products-services/product-offerings/circuit-breakers.html) — Siemens Energy. Public technical context for switching-device operating references. Circuit-breaker construction and interruption families. The application text and educational graphic are independently authored; the publisher does not certify this representation.

## 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.