Protection Coordination Chart

Use this worksheet after the calculator result to record upstream and downstream devices, settings, fault point, clearing time, time margin, and study follow-up.

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Quick reference table

A protection coordination chart is a calculator-led planning worksheet. It preserves the device pair and time-margin result so settings, curves, available fault current, and selective coordination needs can be reviewed.

Protection coordination worksheet

Protection coordination worksheet
Item	Record from calculator	Follow-up
Device pair	Upstream and downstream IDs	Confirm exact model and settings
Fault point	Current and location	Tie to short-circuit study case
Clearing times	Downstream and upstream times	Review curves and tolerances
Margin	Calculated time margin	Check project selectivity criteria
Action	Setting, device, or study note	Route to the responsible protection engineer

Coordination review context

Coordination review context
Review item	Record on worksheet	Why it matters
Device curve source	Manufacturer curve, trip unit, fuse class, relay function	Curves and tolerances drive the time margin
Fault-current point	Current, location, source case	The same device pair behaves differently at another current
Instantaneous region	Instantaneous pickup or override note	Selectivity can disappear outside long-time regions
Study change	Setting revision, device change, or relay test note	A calculator screen should route the next engineering action

Formula basis

Coordination time margin = upstream clearing time - downstream clearing time at the same fault-current point.

Upstream clearing time is the protective-device time above the downstream device.
Downstream clearing time is the device nearest the fault for the selected current point.
Fault-current point must be the same current value for both device curves.
Time margin is a screening result that still needs study and manufacturer curve review.

Worked examples

Feeder-to-branch coordination recordRecord the upstream breaker, downstream fuse, fault current, clearing times, time margin, available fault-current basis, and whether a full coordination study update is needed.

Relay setting review handoffKeep relay function, CT ratio, pickup, time dial, downstream device, fault-current point, and margin in one record before a relay test or study update.

Assumptions. Balanced load and line-to-line voltage assumptions behind this chart.

The worksheet compares a selected device pair and does not replace a full time-current coordination study.
Device curves, tolerances, maintenance condition, ground-fault settings, instantaneous regions, and available fault current can change the coordination outcome.

Code and standard notes. Planning limits that should be checked before final equipment selection.

Use this chart as a calculation record; verify adopted NEC selective-coordination requirements where applicable, IEEE or manufacturer curve data, equipment ratings, OSHA safety controls, AHJ expectations, and qualified-person engineering review before changing settings.

How to use this chart

1Define the device pairIdentify exact upstream and downstream devices, settings, and the system location.

2Tie to a fault pointRecord the available fault-current value and location used for the comparison.

3Route study changesUse the worksheet to list setting changes, curve questions, and engineering review items.

Worksheet checklist. Record source basis, review gaps, and assumptions before using the chart result.

Capture devicesRecord manufacturer, model, rating, trip unit, fuse class, relay function, and settings.
Capture timingWrite downstream clearing time, upstream clearing time, time margin, and current point.
Capture decisionList accept, revise, study, relay test, or manufacturer follow-up status.

Common mistakes to avoid. Review these before turning chart current into an equipment decision.

Comparing device curves at different current values.
Changing settings from a calculator result without reviewing the full coordination and equipment-duty context.
Ignoring instantaneous pickup, ground-fault functions, maintenance settings, or manufacturer curve tolerances when judging a time margin.

Frequently asked questions

These answers explain how to use the chart without turning a quick reference into a final design decision.

Can one time margin prove selective coordination?

No. One point can screen a device pair, but full coordination requires review across relevant current ranges and settings.

Why record the fault-current point?

The time margin only has meaning at the current point being compared. Different current levels can produce different coordination behavior.