# Auxiliary AC source-transfer interface

Canonical URL: https://eloragrid.ai/symbols/auxiliary-ac-source-transfer-interface
Publisher: Elora Grid
Updated: 2026-11-03
Lookup label: AASI
Drawing use: Schematic
Reference families: Manufacturer

Representation: Functional block
Installation focus: switchrooms
Input: Auxiliary-source health
Output: Selected AC bus source

Transfers the assigned room AC bus between documented available sources.

## In plain English

### What this block does

Transfers the assigned room AC bus between documented available sources.

### A simple example

In a switchroom, the lighting, service sockets, charger input and room cooling may be fed from different auxiliary branches. A source change must preserve the identities of loads that require continuity. For this reference, the drawing identifies “Auxiliary-source health” at the input and “Selected AC bus source” at the output. Source interlocking must prevent unintended paralleling.

### What the drawings help you do

Start at the named input: Auxiliary-source health. Identify its source device or document and the state represented on the drawing. Follow the named output: Selected AC bus source. Cross-reference its destination and separate the command from confirmation that the equipment responded.

### Terms

- Input: Auxiliary-source health
- Output: Selected AC bus source
- Application reference: An explanation of a named drawing function or circuit relationship; the project documents define the equipment and its connections.

Concept diagram: Auxiliary-source health → AASI → Selected AC bus source
A reading guide. The entry's original illustration and input/output facts describe this application.

- [SEL-RPM redundant power module](https://selinc.com/products/RPM/)


## What it represents

Transfers the assigned room AC bus between documented available sources. An auxiliary AC distribution diagram identifies the supplies serving room services and control-support equipment. Essential, backed-up and ordinary circuits can have different source paths and operating priorities.
In a switchroom, the lighting, service sockets, charger input and room cooling may be fed from different auxiliary branches. A source change must preserve the identities of loads that require continuity. For this reference, the drawing identifies “Auxiliary-source health” at the input and “Selected AC bus source” at the output. Source interlocking must prevent unintended paralleling.
Label source, branch protection and load purpose. The arrangement does not establish conductor sizes, protection settings or installation compliance; it links the operating role to the selected equipment schedule. 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: Auxiliary-source health. Identify its source device or document and the state represented on the drawing.
- Follow the named output: Selected AC bus source. Cross-reference its destination and separate the command from confirmation that the equipment responded.
- Source interlocking must prevent unintended paralleling.
- Label source, branch protection and load purpose. The arrangement does not establish conductor sizes, protection settings or installation compliance; it links the operating role to the selected equipment schedule.

## Information to show or reference

- Label the source and connection reference for auxiliary-source health.
- Identify the destination and defined state of selected ac bus source.
- Record the equipment or control-document revision supporting this functional block.
- Check this application limit in the project design: Source interlocking must prevent unintended paralleling.

## Important distinction

Source interlocking must prevent unintended paralleling. 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: Switchrooms
- Input / boundary: Auxiliary-source health
- Output / connection: Selected AC bus source
- Lookup label: AASI is a library lookup label, not a standard device designation.

## Public references

- [SEL-RPM redundant power module](https://selinc.com/products/RPM/) — SEL. Public technical context for switchroom auxiliary ac distribution. Independent AC and DC sources for station auxiliary power. 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.