IEC 60330: Time Relays — From Industrial Control to Protection Automation Delay Logic

Milliseconds of Timing Accuracy Determine Protection Selectivity in Substations

IEC 60330:1970 specifies time relay requirements. Time relays provide graded delays in protection systems — primary protection 0 ms, secondary 100–300 ms, tertiary 300–500 ms. This timing staircase ensures protection selectivity — only the breaker closest to the fault trips.

TNLab — Time relay accuracy determines whether “the right breaker trips while the rest keep supplying.”