# Protection-electronics supply branch

Canonical URL: https://eloragrid.ai/symbols/protection-electronics-supply-branch
Publisher: Elora Grid
Updated: 2026-11-03
Lookup label: PSB
Drawing use: Schematic
Reference families: Manufacturer

Representation: Functional block
Installation focus: switchgear
Input: Protected auxiliary supply
Output: Protection-device power

Identifies the supply dedicated to the assigned protective relays and their electronics.

## In plain English

### What this block does

Identifies the supply dedicated to the assigned protective relays and their electronics.

### A simple example

In a switchgear lineup, separate protected branches may feed trip coils, closing coils and protection electronics. Their alarm contacts help the station controller identify which operating capability is unavailable. For this reference, the drawing identifies “Protected auxiliary supply” at the input and “Protection-device power” at the output. Relay power is distinct from trip-coil power.

### What the drawings help you do

Start at the named input: Protected auxiliary supply. Identify its source device or document and the state represented on the drawing. Follow the named output: Protection-device power. Cross-reference its destination and separate the command from confirmation that the equipment responded.

### Terms

- Input: Protected auxiliary supply
- Output: Protection-device power
- Application reference: An explanation of a named drawing function or circuit relationship; the project documents define the equipment and its connections.

Concept diagram: Protected auxiliary supply → PSB → Protection-device power
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

Identifies the supply dedicated to the assigned protective relays and their electronics. Control power supplies the command, protection and indication equipment associated with a switchgear assembly. The drawing must distinguish the source, each distribution branch and the functions lost if that branch fails.
In a switchgear lineup, separate protected branches may feed trip coils, closing coils and protection electronics. Their alarm contacts help the station controller identify which operating capability is unavailable. For this reference, the drawing identifies “Protected auxiliary supply” at the input and “Protection-device power” at the output. Relay power is distinct from trip-coil power.
Follow the actual positive, negative or neutral returns and the protective device on each branch. A healthy voltage indication does not establish that every downstream path can deliver its required operating current. 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: Protected auxiliary supply. Identify its source device or document and the state represented on the drawing.
- Follow the named output: Protection-device power. Cross-reference its destination and separate the command from confirmation that the equipment responded.
- Relay power is distinct from trip-coil power.
- Follow the actual positive, negative or neutral returns and the protective device on each branch. A healthy voltage indication does not establish that every downstream path can deliver its required operating current.

## Information to show or reference

- Label the source and connection reference for protected auxiliary supply.
- Identify the destination and defined state of protection-device power.
- Record the equipment or control-document revision supporting this functional block.
- Check this application limit in the project design: Relay power is distinct from trip-coil power.

## Important distinction

Relay power is distinct from trip-coil power. 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: Protected auxiliary supply
- Output / connection: Protection-device power
- Lookup label: PSB 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 switchgear control-power supervision. 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.