50
Instantaneous overcurrent
An overcurrent function without an intentional operating time delay in its instantaneous application.
Protection functions
Protection functions · 51
Time overcurrent
An overcurrent function with a documented time characteristic.
SLD / Schematic · 51
What it represents
A time overcurrent function detects an overcurrent condition using the configured time characteristic. Depending on the device and application, the implementation can include inverse-time or definite-time behaviour. Its number does not specify a curve, pickup or delay.
On a power drawing, keep this function reference connected to the selected equipment and its complete designation. A multifunction relay can implement several numbered functions. This entry explains the reference; it supplies no settings or commissioning procedure.
How to read it
- Read the full function designation, including any phase or earth-fault suffix.
- Use the protection settings and coordination documentation to interpret its operation.
Information to show or reference
- Reference measured current inputs.
- Identify the applied time characteristic separately.
- Link the relay and trip scheme.
A distinction that matters
Functions 50 and 51 describe different time behaviour. One multifunction relay can implement both without becoming two separate physical devices.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Public reference table of ANSI device-function numbers
Public manufacturer table used to check the base function-number name.
IEEE C37.2-2022: power-system device function numbers
Normative publication reference for the device-function convention.
Relion 620: functions, codes and symbols
Public examples of manufacturer-specific function names and suffixes.
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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