Chart
Selective coordination time-current curves chart
Read main, feeder, and branch protective-device curves as a visual coordination lookup.
Chart boundary
Does not perform a coordination study, select protective devices, calculate incident energy, or approve settings.
time current log curve
Main-feeder-branch curve spacing
The chart teaches curve reading: downstream devices should clear faults before upstream devices where coordination is required.
Scopeprotection and fault currentX-axisRMS current ampsY-axisclearing time secondsReviewAnnualNextAvailable fault current margin calculator
Overloadlong time
Thermal curve region.
Short timemargin zone
Coordination separation matters.
Instantaneousconflict risk
Selectivity can be lost quickly.
Decision table
Explain how time-current curve overlap, separation, and instantaneous regions affect coordination review.
Scroll sideways to keep row labels aligned with hidden columns.
| Curve band | What it shows | Risk cue | Handoff |
|---|---|---|---|
| Branch curve | Closest device to the fault | Should clear first where required | Device curve data |
| Feeder curve | Intermediate backup device | Overlap can cause wider outage | Coordination study |
| Main curve | Upstream service or distribution device | Trip affects large area | Protection engineer review |
| Instantaneous pickup | Fast high-current trip zone | Selectivity can be lost | Manufacturer software |
Notes
- Treat this chart as a planning and conversation aid only.
- Confirm current utility requirements, product markings, manufacturer instructions, and local authority requirements before field work.
- Use the linked calculator or table when the task needs project-specific arithmetic.
Source links
Open the underlying public sources before treating the chart as project guidance.