SS
Selector switch
An operator switch selecting between documented control positions.
Schematic
Protection functions · 3
Checking or interlocking relay
Checks a required equipment state before the operating sequence proceeds.
SLD / Schematic · 3
What it represents
Checks a required equipment state before the operating sequence proceeds.
In a drafting package, connect this reference to the equipment status contacts used as permissives. The associated drawing should trace the blocked or permitted command path; the number identifies the role and does not specify the terminal arrangement, ratings or operating settings.
How to read it
- Identify the equipment status contacts used as permissives.
- Trace the blocked or permitted command path.
Information to show or reference
- Label the equipment status contacts used as permissives.
- Cross-reference the blocked or permitted command path.
- Identify the device tag, manual revision and logic drawing that define this implementation.
A distinction that matters
An interlock verifies a condition; a time delay by itself does not prove that condition.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
ANSI device-number and suffix reference table
Public manufacturer number/name association. Drafting explanations are independently written.
IEEE C37.2-2022: power-system device function numbers
Normative device-number publication; exact edition wording and compliance require the licensed standard.
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.
Explore related references
Put the reference into a drawing workflow.
Elora Grid helps electrical teams work with drawings, specifications and equipment information. Explore the drafting workflow or join the early-access waitlist.