NO
Normally open contact
A contact shown open in the normal state defined for its device.
Schematic
Symbols · CO
Changeover contact
A contact arrangement switching a common connection between two contact paths.
Schematic · CO
What it represents
A changeover contact connects a common terminal to one of two alternative contact paths according to its operating state. Form C and SPDT are terms commonly encountered for this arrangement. The actual terminal numbering and transfer behaviour come from the selected device.
The schematic should make the common terminal and normal state clear. A mirrored or differently oriented drawing can retain the same logical arrangement, but terminal associations must not be inferred from appearance alone.
How to read it
- Locate the common terminal and determine the path shown in the defined normal state.
- Use device data to identify transfer timing and any special overlap behaviour.
Information to show or reference
- Identify the common terminal.
- Link both switched paths to the parent device.
- Keep terminal identifiers consistent with wiring documentation.
A distinction that matters
Two unrelated NO/NC contacts are not automatically one changeover contact. Confirm whether they share a common connection and operating mechanism.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Relays and contacts: public symbol reference
Public Form C relay contact variants.
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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