Safety & Protection calculator
Protection Coordination Calculator
At one 12 kA review point, 0.18 s downstream clearing and 0.42 s upstream clearing give a 0.24 s coordination interval; a manufacturer-published 25 kA selective pair also screens inside 18 kA available fault current. This page is a one-point protection-coordination screen. It helps you compare coordination time margin, manufacturer-published selective current, and instantaneous pickup settings at a single review point. It does not replace a full time-current-curve study, a relay coordination package, or manufacturer-specific settings engineering.
Updated August 17, 2026
If downstream clears in 0.18 s and upstream clears in 0.42 s at the same 12 kA point, the coordination time interval is 0.24 s. A published 25 kA selective pairing also screens as acceptable against 18 kA available fault current.
This page screens one point only: time margin = upstream time - downstream time | published selective current compares available fault current against manufacturer data.
Choose time margin published selective current or instantaneous pickup below for a one-point coordination screen
Example Calculations
How to Use
How to use the protection coordination calculator
- Choose the screen that matches the question you are actually trying to answer:
- Coordination Time Margin when you already know upstream and downstream total clearing times at one common fault current
- Published Selective Current when a manufacturer has published a selective-current or selective-kA value for an exact device pair
- Instantaneous Pickup when you need to check whether a pickup setting stays above temporary non-fault current while remaining below available fault current
- Enter only data from the same review point. Do not mix clearing times or selective ratings taken from different buses, devices, or fault-current assumptions.
- Read the result as a screening outcome, not as final study approval.
- Move to manufacturer TCCs, relay settings files, short-circuit data, and project documentation before releasing a final design.
What each mode does
| Mode | What you enter | What the page returns | What it does not replace |
|---|---|---|---|
| Coordination Time Margin | Common fault current, downstream clearing time, upstream clearing time, required minimum margin | Coordination time interval, margin ratio, and pass/review screen | A full TCC overlay or settings study across the whole system |
| Published Selective Current | Available fault current and the exact published selective-current rating | Current margin, published-to-available ratio, and within-range review | Substituting one manufacturer, trip unit, or frame size for another |
| Instantaneous Pickup | Maximum temporary non-fault current, instantaneous pickup, available fault current | Headroom above non-fault current, fault-to-pickup ratio, and pass/review screen | A complete motor-starting, transformer-inrush, or relay-coordination package |
Scope notes that matter
- This page does not plot time-current curves.
- This page does not determine selective coordination across every fault-current level in a distribution system.
- Published selective-current results are valid only for the exact manufacturer-published device pair and settings basis.
- Instantaneous pickup review depends on having a realistic non-fault current envelope such as motor inrush, transformer inrush, or a temporary overload block you expect the device to ride through.
Example 1: if the downstream device clears in 0.18 s and the upstream device clears in 0.42 s at the same 12 kA point, the coordination time interval is 0.24 s. If the required minimum is 0.20 s, that point passes the screen.
Example 2: if a manufacturer publishes 25 kA selective coordination for an exact breaker pair and the available fault current is 18 kA, the point stays within the published selective-current range. If the available fault current rises above that published value, this page flags the point for review.
Example 3: if a breaker has an instantaneous pickup of 1600 A, must ride through a 600 A non-fault current, and sees 5000 A available fault current, the setting stays above the non-fault envelope while remaining below the available fault current, so the one-point screen is acceptable.
Use the Short Circuit Calculator when the real question is available fault current. Use the Relay Testing Calculator when the real question is secondary-current relay pickup and timing. Use the Arc Flash Calculator when the real question is incident energy rather than device selectivity.
Common Applications
Frequently Asked Questions
What does this calculator actually verify?
It verifies a single screening condition at a single review point. It does not certify full selective coordination across all current levels and all devices in the system.
When should I use published selective current instead of time margin?
Use published selective current when a manufacturer provides a selective-current or selective-kA rating for the exact device pair you are using. Use time margin when you already know upstream and downstream clearing times at a common fault-current point.
Can I use this page as a full time-current-curve study?
No. A real TCC study requires the full device curves, minimum and maximum fault-current review, equipment tolerances, and the actual device settings or trip units used on the project.
Why can instantaneous pickup fail even when fault current is high?
Because the setting also has to ride through expected non-fault current such as motor or transformer inrush. A setting can be low enough to see a fault and still be too low to avoid nuisance operation.
What should I do after a passing result?
Confirm the same conclusion with the exact manufacturer data, project short-circuit values, device settings, and the adopted coordination method for the installation before treating it as a final design decision.
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