Understand the difference.
Compare the meaning, drawing context and source references of two entries. A similar graphic or shared abbreviation does not establish equivalence.
21YN
Protection functionsAdmittance-based earth-fault protection
Uses earth-fault voltage and current relationships to assess an admittance-based directional criterion.
- Drawing use
- SLD / Schematic
- Application
- Metering & protection
- Reference family
- IEEE / ANSI / Manufacturer
A distinction that matters
ABB documents 21YN for EFPADM; this admittance earth-fault function is distinct from a generic line-distance zone.
21
Protection functionsDistance protection
Uses measured voltage and current to assess an electrical distance or impedance characteristic.
- Drawing use
- SLD / Schematic
- Application
- Metering & protection
- Reference family
- IEEE / ANSI
A distinction that matters
Distance protection uses impedance-related criteria; directional overcurrent 67 uses current and directional supervision.
Original educational previews. Follow the source references on each full entry for the appropriate standard or selected product.