FE
Functional earth
Functional earth serves an operational purpose such as a documented EMC or signal-reference connection.
SLD / Schematic
IEC · -
Noiseless earth
An earth connection specifically designated as low-noise, used for sensitive measurement and electronics references.
In plain English
What does Noiseless earth mean?
The noiseless or clean earth symbol identifies a connection to an earth that is kept free of noise from power circuits, usually an instrument earth bar connected to the main earthing system at a single point. It is drawn as an earth symbol enclosed in a circle or with a distinguishing mark.
A simple example
A noiseless earth is not a separate earth electrode. Separate electrodes not bonded to the main earth create dangerous potential differences during faults. The symbol identifies the bar and its single-point connection, which the earthing diagram should show.
What the drawings help you do
Find the single point where the clean earth joins the main earth. Reject any isolated clean earth electrode. A noiseless earth is a dedicated low-noise bar bonded to the main earth; a functional earth is any earth used for operation rather than safety.
This particular reference
An earth connection specifically designated as low-noise, used for sensitive measurement and electronics references. A noiseless earth is a dedicated low-noise bar bonded to the main earth; a functional earth is any earth used for operation rather than safety.
- Terminal
- An identified point where a conductor connects.
- Schematic
- A drawing showing function and connections rather than physical appearance.
Read the source: AutoCAD Electrical: Earthing, sources and surge protection · Earthing connections
IEC · Noiseless earth
Independent IEC-context illustration; not certified IEC geometry.
Shown as an independently authored educational illustration. Use the cited publication and drawing legend to verify the required drafting form.
Schematic · -
What it represents
The noiseless or clean earth symbol identifies a connection to an earth that is kept free of noise from power circuits, usually an instrument earth bar connected to the main earthing system at a single point. It is drawn as an earth symbol enclosed in a circle or with a distinguishing mark.
A noiseless earth is not a separate earth electrode. Separate electrodes not bonded to the main earth create dangerous potential differences during faults. The symbol identifies the bar and its single-point connection, which the earthing diagram should show.
How to read it
- Find the single point where the clean earth joins the main earth.
- Reject any isolated clean earth electrode.
Information to show or reference
- Show the clean earth bar and its bond.
- Keep power returns off the clean earth.
- Label which circuits use it.
A distinction that matters
A noiseless earth is a dedicated low-noise bar bonded to the main earth; a functional earth is any earth used for operation rather than safety.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
AutoCAD Electrical: Earthing, sources and surge protection
Public IEC-oriented earth and functional-earth forms.
Earthing connections
Public installation-guide earthing connection elements.
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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