ATS
Transfer-switch assembly
An equipment assembly connecting a load to the selected supply source.
GA objects
Symbols · ATS
Automatic transfer switch
A mechanically switched changeover device that automatically moves a load from a failed normal source to an alternate source.
In plain English
What does Automatic transfer switch mean?
An automatic transfer switch monitors the normal supply and, when voltage or frequency goes out of limits, signals the generator to start and transfers the load to the alternate source once it is ready. When the normal supply returns and is stable, it transfers back after a time delay. Most units use an open-transition break-before-make sequence.
A simple example
Single-line diagrams show a changeover contact with two incoming poles labelled N and E or S1 and S2 and one outgoing load connection, or two interlocked switching devices. The controller and generator start signal are often noted beside it, and a neutral pole may be switched for separately derived systems.
What the drawings help you do
The symbol does not show the timing, whether the neutral is switched, or whether the transition is open, closed or delayed. Those features determine earthing behaviour, motor reconnection and coordination with the network operator.
This particular reference
A mechanically switched changeover device that automatically moves a load from a failed normal source to an alternate source. An automatic transfer switch operates without an operator; a manual transfer switch needs someone to move it.
- Normally open / normally closed
- The contact state in the normal condition defined for the drawing.
- Terminal
- An identified point where a conductor connects.
- Signal
- Electrical information passed between devices, rather than necessarily the main power supply.
Read the source: Transfer switch fundamentals · ATS controllers
SLD / Schematic · ATS
What it represents
An automatic transfer switch monitors the normal supply and, when voltage or frequency goes out of limits, signals the generator to start and transfers the load to the alternate source once it is ready. When the normal supply returns and is stable, it transfers back after a time delay. Most units use an open-transition break-before-make sequence.
Single-line diagrams show a changeover contact with two incoming poles labelled N and E or S1 and S2 and one outgoing load connection, or two interlocked switching devices. The controller and generator start signal are often noted beside it, and a neutral pole may be switched for separately derived systems.
The symbol does not show the timing, whether the neutral is switched, or whether the transition is open, closed or delayed. Those features determine earthing behaviour, motor reconnection and coordination with the network operator.
How to read it
- Check whether three or four poles are switched.
- Read the transition type from the notes.
Information to show or reference
- State current rating, poles and transition type.
- Show both sources and the generator start signal.
- Reference controller timing settings.
A distinction that matters
An automatic transfer switch operates without an operator; a manual transfer switch needs someone to move it.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Transfer switch fundamentals
Public transfer switch fundamentals.
ATS controllers
Public automatic transfer controller page describing mains and generator transfer.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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MTS
Manual transfer switch
An operator-moved changeover switch that selects which of two sources supplies a load, with an off position between them.
SLD / Schematic
CTTS
Closed-transition transfer switch
A transfer switch that briefly parallels two synchronised sources so the load moves without interruption.
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Automatic selective control or transfer relay
Automatically selects between control circuits or operating sources under defined conditions.
Protection functions
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