IDMT Overcurrent Relay Setting Calculator
Compute relay pickup current and predict trip time at fault current for IEC IDMT overcurrent relays. Covers SI, VI, and EI curve families per IEC 60255.
Protection Relay Setting
Results
Pickup Setting (Ir)1.25 A
Pickup Current Ir (relay A):1.25 A
Trip current (primary A):125 A
Fault current / Ir (M):25×
Trip time at max fault:0.28 s
Instantaneous Isd (≥10× Ir):12.5 A relay / 1250 A primary
IEC 60255 IDMT (SI)
t = TMS × 0.14 / (M^0.02 − 1)