IEC 60255-151:2009 / IEEE C37.112-2018
The two standards that define inverse-time overcurrent characteristics. AmpSize uses them to plot relay trip curves and to measure the grading margin between relays.
Notes
- Edition cited
- IEC 60255-151:2009 / IEEE C37.112-2018
- Amendments applied
- No amendment named in the source (1 table)
- Tables last checked
- 26 Sept 2026
- Tables
- 1: 1 verified
- Clauses
- 1
No text of the standard is reproduced here. AmpSize is a design aid. Verify results against the current standard.
Contents (2)
Clauses (1)
Inverse-time overcurrent curves
The IDMT tool plots relay curves from these two standards. Each curve name sets three constants. The tool puts those constants into the trip time equation and draws the result against current.
Tools that read it:
Tables (1)
IDMT overcurrent curve constants
The IDMT tool reads the three constants that shape each named relay curve.
Verified: read against the printed standard, pages 29 (PDF 31), Annex A Table A.1. Checked 26 Sept 2026.
Tools that read it: