Cable short-circuit rating calculator

Use this calculator when a conductor short-circuit withstand current needs a traceable worksheet record before the result is carried into protection review, cable selection or project documentation. The page uses the entered conductor area, k value and clearing time to estimate a withstand current, then compares that result with the entered available fault current.

The page is deliberately narrow. It does not choose a protective device, set a clearing time, select a cable size or complete the protection coordination work. It records the arithmetic consequence of the entered values so another reviewer can see whether the conductor deserves more attention.

Short-circuit rating use cases

A useful record names the conductor and calculation point. "Short-circuit checked" is weak. "CAB-SC-1, 16 mm2, k=115, 0.4 s clearing time, 2.5 kA available fault current, 2.909 kA withstand and 0.409 kA margin" can be reviewed when the device or conductor basis changes.

Cable withstand data checklist

The calculator is strongest when the current and time come from the same point in the installation. A fault current taken at one board and a clearing time taken from a different device can make a tidy result that does not belong to the actual conductor.

Method matrix

The method is a worksheet, not a selector. If the result is outside the entered withstand basis, the next action is to review conductor area, k value, clearing time and fault-current basis. The calculator does not decide which replacement conductor, device or installation method should be used.

Worked records

These records show why conductor area alone is not enough. The same area can behave very differently when k or clearing time changes. A short clearing time can narrow the energy basis quickly, while a larger conductor or stronger k value can widen it.

Review workflow

1. Identify the conductor and calculation point from the board, circuit or cable schedule.
2. Confirm the conductor area being screened.
3. Enter the k value from the project, standards or manufacturer basis.
4. Enter the protective-device clearing time for the same fault condition.
5. Enter the available fault current at the same calculation point.
6. Read withstand current, event energy, current margin and utilisation together.
7. If the available fault current is above the calculated withstand current, recheck conductor area, k value, clearing time and the fault-current basis before changing the record.
8. Move protective-device selection, cable selection and coordination work into the relevant project review.

This workflow keeps the calculator as an arithmetic screen. It helps identify whether the conductor deserves more attention, but it does not replace protection design or conductor selection.

Boundary with neighbouring calculators

Keeping this boundary clear prevents a useful conductor screen from becoming an unsupported device or cable selection tool. The output should travel with its assumptions, not as a standalone answer.

Australian context

Cable short-circuit work in Australia can involve AS/NZS 3008 cable-selection context, AS/NZS 3000 installation context, protective-device manufacturer data, available fault current studies, DNSP conditions, authority requirements and project documentation. This calculator stays with transparent arithmetic and user-entered values. It does not reproduce protected tables, device curves, let-through tables or final protection decisions.

The safest public model is to make the source values visible. The user enters conductor area, k value, clearing time and available fault current. The result can then be reviewed beside cable schedules, protection records and local requirements.

Minimum export record

Stop points

• The fault-current point is not the same as the conductor location.
• The clearing-time source is uncertain or belongs to a different device setting.
• The k value is copied from a different conductor material or insulation basis.
• The conductor area is a nominal value that does not match the actual record.
• The available fault current exceeds the calculated withstand current.
• The result is being used as final cable selection or device selection without wider review.
• DNSP, local authority, manufacturer or current standards requirements are being treated as optional.

The useful output is a repeatable conductor rating record. Keep the area, k value, clearing time and fault current together so another reviewer can repeat the result when the project basis changes.