What can this calculator do?

This page checks that the protection chain actually works: that each device trips, that it trips before the device upstream of it, and that it is sensitive enough to see the smallest fault it has to clear. The device chain runs from the source through the transformer, switchgear, breakers and loads, and it uses the rated current and settings of each device (thermal setting multiple, long-time delay, magnetic trip multiple, short-time delay) together with the fault currents from the short-circuit study. The trip-curve library engines/tcc-library.js is the source of the curves, driven by studyOptions.enableProtectionCoord and the protection study. Typical uses: proving selectivity across a switchboard before it is ordered, and finding the device whose setting breaks the grading.

What does a passing result actually prove?

That the chain satisfies three separate things at once: every device operates for the fault it is responsible for, each operates earlier than the device upstream of it, and each is sensitive enough for the smallest fault it must clear. A curve envelope that looks tidy can still fail one of the three, which is why they are reported as separate checks rather than one verdict.

Why does coordination matter so much in practice?

Protection that does not coordinate fails in two directions: too slow or too high a setting and the fault is not cleared at all, while too much overlap makes the upstream device trip first and takes out a healthy part of the installation. Selectivity is what keeps one fault from becoming a site-wide outage, and sensitivity is what keeps a high-impedance fault from going unnoticed.

Protection, safety & stability

Coordination, arc flash, N-1, grounding and motor starting

Step 1 of 3Protection, safety & stability

Pick a scheme first — then this column can calculate

This column runs the real engine on your project scheme, and there is none yet — that is why no calculation buttons are shown here (they are not broken). Start with any of the ways below; the fastest is the built-in example (one click, real parameters).

① Load a real example scheme (fastest)

10 kV incoming (200 MVA short-circuit level) → 1250 kVA transformer (Dyn11) → LV main switchboard → busbar → 5 feeders plus a fire/emergency ATS branch. 1000 kW calculated load, cosφ 0.85, power-factor target 0.95.

Load the real example scheme and start calculating →

Or pick a ready-made scheme in the scheme library →

The scheme and its parameters go straight into your browser; replace the data with your own at any time.

Calculator mode

Calculator mode computes the few outputs that only depend on parameters you type in yourself. Anything that genuinely needs the whole system (full-network load flow, coupling with other devices) is shown as “needs a scheme” and no number is given.

Calculator mode is not available for this column yet — use one of the ways below.

Nothing is pre-filled and nothing is invented: leave a required field empty and the result area says “unavailable”.

② Or build your own scheme

In the studio, place devices, wire them and pick models — that becomes your project scheme (drawings / BOM / report can be exported).

Open the studio →

Need a hand?

Use the chat bubble bottom-right, or Contact us — we will set the example to your site parameters.

Note: every number comes from the engine. With no scheme, nothing is invented here.

Frequently asked questions

What can this calculator do?: This page checks that the protection chain actually works: that each device trips, that it trips before the device upstream of it, and that it is sensitive enough to see the smallest fault it has to clear. The device chain runs from the source through the transformer, switchgear, breakers and loads, and it uses the rated current and settings of each device (thermal setting multiple, long-time delay, magnetic trip multiple, short-time delay) together with the fault currents from the short-circuit study. The trip-curve library engines/tcc-library.js is the source of the curves, driven by studyOptions.enableProtectionCoord and the protection study. Typical uses: proving selectivity across a switchboard before it is ordered, and finding the device whose setting breaks the grading.
What does a passing result actually prove?: That the chain satisfies three separate things at once: every device operates for the fault it is responsible for, each operates earlier than the device upstream of it, and each is sensitive enough for the smallest fault it must clear. A curve envelope that looks tidy can still fail one of the three, which is why they are reported as separate checks rather than one verdict.
Why does coordination matter so much in practice?: Protection that does not coordinate fails in two directions: too slow or too high a setting and the fault is not cleared at all, while too much overlap makes the upstream device trip first and takes out a healthy part of the installation. Selectivity is what keeps one fault from becoming a site-wide outage, and sensitivity is what keeps a high-impedance fault from going unnoticed.