# Bypass-isolation transfer switch

Canonical URL: https://eloragrid.ai/symbols/bypass-isolation-transfer-switch
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: BP/ATS
Drawing use: SLD
Reference families: IEC, IEEE / ANSI

An automatic transfer switch paired with a manual bypass switch so the ATS can be isolated for maintenance without losing the load.

## In plain English

### What does Bypass-isolation transfer switch mean?

A bypass-isolation transfer switch combines an automatic transfer switch with a parallel manual bypass switch. The bypass can connect the load directly to either source while the automatic switch is withdrawn or isolated, so maintenance and testing can proceed without interrupting critical loads such as hospital or emergency circuits.

### A simple example

Single-line diagrams draw the automatic changeover in one path and a manually operated changeover in parallel, with isolating contacts on the automatic unit. Interlocks prevent the bypass from connecting the load to a source different from the one the automatic switch is using at the moment of bypass.

### What the drawings help you do

The symbol does not show the interlock sequence or whether the bypass operation is load-break. Operators need the switching procedure to use it safely.

### This particular reference

An automatic transfer switch paired with a manual bypass switch so the ATS can be isolated for maintenance without losing the load. A bypass-isolation switch adds a manual path around the ATS; a plain ATS must be not supplied with operating power for maintenance.

### Terms

- Normally open / normally closed: The contact state in the normal condition defined for the drawing.
- Rating: A value stating the conditions for which equipment is specified.
- Schematic: A drawing showing function and connections rather than physical appearance.

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.

- [Transfer switch fundamentals](https://www.cummins.com/sites/default/files/2026-04/2023-sep-transfer-switch-fundamentals.pdf)
- [Generator switchgear and paralleling controls](https://www.cummins.com/en-na/generators/products/switchgear)


## What it represents

A bypass-isolation transfer switch combines an automatic transfer switch with a parallel manual bypass switch. The bypass can connect the load directly to either source while the automatic switch is withdrawn or isolated, so maintenance and testing can proceed without interrupting critical loads such as hospital or emergency circuits.
Single-line diagrams draw the automatic changeover in one path and a manually operated changeover in parallel, with isolating contacts on the automatic unit. Interlocks prevent the bypass from connecting the load to a source different from the one the automatic switch is using at the moment of bypass.
The symbol does not show the interlock sequence or whether the bypass operation is load-break. Operators need the switching procedure to use it safely.

## How to read it

- Identify the isolating contacts that allow the automatic unit to be withdrawn.
- Bypass and automatic paths should be interlocked.

## Information to show or reference

- State ratings for both paths.
- Show isolation contacts and interlocks.
- Reference bypass procedure.

## Important distinction

A bypass-isolation switch adds a manual path around the ATS; a plain ATS must be de-energised for maintenance.

## Facts

- Paths: Automatic and manual bypass
- Purpose: Maintenance without load loss
- Interlocks: Source matching between paths
- Preview: Independent educational illustration; consult the applicable standard and project legend for the exact graphic

## Public references

- [Transfer switch fundamentals](https://www.cummins.com/sites/default/files/2026-04/2023-sep-transfer-switch-fundamentals.pdf) — Cummins. Public transfer switch fundamentals.
- [Generator switchgear and paralleling controls](https://www.cummins.com/en-na/generators/products/switchgear) — Cummins. Public generator switchgear context.

## 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.