50
Instantaneous overcurrent
An overcurrent function without an intentional operating time delay in its instantaneous application.
Protection functions
Protection functions · 50N
Instantaneous neutral overcurrent
Supervises the neutral or residual-current quantity identified by the protection scheme.
SLD / Schematic · 50N
What it represents
Supervises the neutral or residual-current quantity identified by the protection scheme.
The drafting record should connect this function to the neutral CT or calculated residual-current source, then trace the neutral overcurrent trip and residual measurement reference. Keep the complete designation and equipment tag together so that the SLD, relay logic and terminal schedule describe the same implementation.
The cited mapping is a public manufacturer example (SEL public device-number table). Suffixes are not universal equivalences across products, and this reference supplies neither a protection setting nor certification of the selected scheme.
How to read it
- Identify the neutral CT or calculated residual-current source.
- Trace the neutral overcurrent trip and residual measurement reference.
Information to show or reference
- Label the neutral CT or calculated residual-current source.
- Cross-reference the neutral overcurrent trip and residual measurement reference.
- Retain the complete suffix, selected device tag and manufacturer manual revision.
A distinction that matters
The letter N alone does not prove whether current is measured directly or calculated from phase inputs.
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 primary-source function or application mapping used to identify this designation; wording and drafting notes are original.
IEEE C37.2-2022: power-system device function numbers
Device-number and suffix convention. This page is not a reproduction of the full 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.
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