Switchboard & Fault Scenario Sizing Calculator

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Preliminary engineering aid — not a formal fault study. This tool follows the newly supplied “Switchboard and Fault Scenario Sizing” workbook. It uses simplified lumped sequence-impedance calculations and the workbook’s direct multiplier for approximate peak current. Utility, transformer, motor and detailed inverter fault behaviour are not automatically modelled.

1. Source / Sequence Inputs

System VLLV

Inverter countNo.

Inverter ratingkVA

Inverter rated currentA

Known 3-phase fault currentkA RMS

Known phase-earth fault currentkA RMS

Calculated Z1%

Calculated Z2%

Calculated Z0%

Approx peak multiplier× Isc

Fault-source factorp.u.

Board sizing factorp.u.

Board PFlag

Board VLLV

Board current basis

The attached workbook applies 1.25 once to establish the fault-study kVA and then applies 1.25 again for switchboard kVA. These two factors are shown separately so the basis is visible. Its “Assumed X/R = 2.2” value is used directly as Ipk = Isc(3φ) × 2.2; this is presented as a workbook multiplier, not as a complete IEC peak-current derivation.

2. Project Notes

Project / panel

Form

Prepared by

Calculated Fault Levels

3-phase Isc

—

kA RMS

Phase-phase

—

kA RMS

Phase-earth

—

kA RMS

Approx peak

—

kA, workbook multiplier

Aggregate inverter nameplate

—

CALC

Fault-study kVA basis

—

ASSUMPTION

3-phase fault current

—

Phase-phase fault current

—

Z1+Z2

Phase-neutral fault current

—

Z1+Z2+Z0

Phase-earth fault current

—

SAME BASIS

Approximate peak / asym value

—

NOT IEC PEAK

The workbook's peak calculation is simply 3-phase Isc × the entered multiplier. Formal IEC 60909 peak current uses a separate kappa relationship and network R/X data.

Preliminary Switchboard Basis

Switchboard power basis

—

ASSUMPTION

Calculated board current

—

Combined inverter rated current

—

NAMEPLATE

Board current ÷ inverter nameplate current

—

INFO

VERIFY DESIGN BASIS

No automatic standard switchboard size is selected. Final rated current, short-time withstand, peak withstand, form of separation, temperature rise, busbar system, protection, arc-fault requirements and assembly verification remain the switchboard manufacturer's / designer's responsibility.

Engineering Limitations

Sequence impedance: Z1, Z2 and Z0 must be on a consistent base. The simplified equations do not replace a network fault study.

Inverter contribution: grid-following/grid-forming inverter fault current is control- and time-dependent. Do not treat a nameplate kVA and a fixed impedance as universally representative without OEM confirmation.

Switchboard: verify the final assembly against the applicable AS/NZS 61439 requirements and project/network requirements.

Important notice and disclaimer
This calculator is provided by JETS Energy as a general engineering planning aid only. Results are generated from user-entered data, workbook-derived assumptions and simplified calculation methods and may not reflect all utility, transformer, generator, inverter, motor, protection, installation, manufacturer, statutory or site-specific requirements. JETS Energy does not warrant or guarantee that the information, calculations or results are accurate, complete, current or suitable for any particular purpose. Users must independently verify the calculation basis, sequence impedances, equipment fault contributions, applicable Standards, manufacturer limits, switchboard ratings and all results before relying on the calculator for design, procurement, construction, certification or operation. To the maximum extent permitted by law, JETS Energy excludes liability for loss, damage, cost or expense arising from use of, or reliance on, this calculator or its results. Nothing in this notice excludes, restricts or modifies any right, guarantee, liability or remedy that cannot lawfully be excluded under the Australian Consumer Law or other applicable law.