Understand the difference.

Compare the meaning, drawing context and source references of two entries. A similar graphic or shared abbreviation does not establish equivalence.

STS

Symbols

Static transfer switch

A static transfer switch uses back-to-back thyristor pairs on each of two sources to move a critical load from one supply to the other in a few milliseconds. It is used in data centres and process plants, typically downstream of two UPS systems, so that a failure in one UPS or its distribution does not interrupt the load.

Drawing use

SLD / Schematic

Application

Microgrid systems

Reference family

IEC / IEEE / ANSI

A distinction that matters

A static transfer switch uses thyristors and transfers in milliseconds; an automatic transfer switch uses mechanical contacts and takes much longer.

Full referenceAdd to legend

ATS

Symbols

Automatic transfer switch

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.

Drawing use

SLD / Schematic

Application

Microgrid systems

Reference family

IEC / IEEE / ANSI

A distinction that matters

An automatic transfer switch operates without an operator; a manual transfer switch needs someone to move it.

Full referenceAdd to legend

Original educational previews. Follow the source references on each full entry for the appropriate standard or selected product.