Working tools for cable current-carrying capacity, voltage drop, maximum demand, voltage rise, short circuit, generator sizing, power conversion and preliminary solar and battery sizing — built on Australian standards methods by the STILL LEC engineering team.
Disclaimer — read before use. These calculators provide preliminary guidance only. Results must be checked and verified by a Registered Professional Engineer before use in any design, installation, certification or purchase decision. Calculation methods follow AS/NZS 3008.1.1:2017, AS/NZS 3000:2018 and AS/NZS 4777.1:2024. STILL LEC Pty Ltd accepts no liability for any loss or damage arising from use of these tools or reliance on their results. Need the numbers certified? STILL LEC provides RPEQ-certified electrical engineering across the Darling Downs and beyond.
Current Carrying Capacity Calculator (AS/NZS 3008) — multiple circuits
Cable capacities from AS/NZS 3008.1.1:2017 Tables 4–14 (Cu and Al, V-75 and X-90, 40°C air / 25°C ground). Add a line per circuit — each shows its capacity, pass/fail against the load, and the smallest size that complies.
#
Circuit description
Cable type
Insulation
Conductor
Installation method
Size mm²
Derate k
Load A
Capacity
Result
Add circuits above.
Derate k = combined factor for grouping, ambient and depth of laying (AS/NZS 3008 Tables 22–28). Copper values are solid/stranded. Cables in contact with thermal insulation need the reduced columns — ask STILL LEC.
Voltage Drop Calculator (AS/NZS 3008) — up to 5 circuits in series
Add a line for each circuit in the run (e.g. main switchboard → MCC → motor, up to 5 in series). Method: Vd = I × L × Vc / 1000 per AS/NZS 3008.1.1:2017 (single-phase = three-phase value × 1.155); the total is checked against the AS/NZS 3000 Clause 3.6.2 limit (5%, or 7% with a dedicated substation/transformer).
#
Circuit description
Conductor
Construction
Temp °C
Size mm²
Current A
Length m
Vd (V)
Vd (%)
Enter circuit details above.
Temp = conductor operating temperature: 75°C typical for V-75 (PVC), 90°C for X-90 (XLPE). Current need not exceed connected load, maximum demand, or protective device rating (AS/NZS 3000 Cl. 3.6.2).
Voltage Rise Calculator (AS/NZS 4777.1) — solar & inverter systems
Add each circuit from the point of supply to the inverter AC terminals (up to 4). The summed voltage rise must not exceed 2% of nominal voltage per AS/NZS 4777.1:2024.
#
Circuit description
Conductor
Construction
Temp °C
Size mm²
Current A
Length m
Rise (V)
Rise (%)
Enter circuit details above.
Segments run from the point of supply toward the inverter (e.g. main switchboard → sub board → inverter). Use inverter rated output current, or export-limited current where applicable.
Prospective Short Circuit Current Calculator
Three-phase bolted fault at the source terminals: Ik = FLA ÷ Zpu = (kVA × 1000) ÷ (√3 × V × Z%/100). Transformer assumes an infinite upstream bus (conservative).
Transformer: nameplate impedance (typ. 4–6%). Generator: sub-transient reactance X″d from the alternator datasheet (default 12%) — result is the initial symmetrical value; generator fault current decays quickly and the sustained level depends on the excitation system. Motor contribution, X/R peak factor and downstream attenuation excluded. Cable-run attenuation coming with verified AS/NZS 3008 R and X data.
Generator Sizing Calculator — with motor starting
Enter each load with its starting method — the calculator finds the worst starting event and recommends a set size. Running kVA = Σ(kW ÷ pf); worst event = all other loads running + the largest single start; recommended set = larger of running kVA × margin or the transient requirement. Preliminary only — confirm against alternator capability and voltage dip limits.
#
Load description
Qty
kW each
pf
Starting
Start ×
Run kVA
Start kVA
Add loads above.
Default start multipliers: DOL 6× run kVA, soft starter 3×, VSD 1.5×, none 1× — editable per load; adjust to match the actual equipment. Multiple-quantity loads assume one unit starts at a time (others running).
kW to Amps / kVA Calculator — three-phase & single-phase
P = √3 × V × I × pf (three-phase) or V × I × pf (single-phase). Enter voltage, power factor and any one of kW, kVA or A.
Enter voltage, pf and one quantity.
Motor Full Load Current Calculator
I = P × 1000 ÷ (√3 × V × η × pf). Efficiency and power factor are editable assumptions — use nameplate data where available.
Transformer Full Load Current Calculator
I = S × 1000 ÷ (√3 × V) three-phase, or S × 1000 ÷ V single-phase.
Power Factor Correction (kvar) Calculator
kvar = P × (tan φ₁ − tan φ₂). Preliminary bank sizing; confirm against measured interval data and harmonics before specifying.
Solar & Battery (BESS) Sizing Calculator
Enter what the site uses and when — the sizer works out the array, battery and inverter. A 15% all-in system loss (performance ratio 0.85) is built in. Feasibility-grade only.
System type
• Solar PV + battery — solar runs the site by day and charges a battery that carries it overnight.
• Solar PV only — solar runs the site by day; overnight power still comes from the grid. Sizing objective
• Offset consumption — size the system to generate a chosen percentage of the site's usage.
• Zero bill — size the system so export credits cancel what's left of the bill, targeting $0.
Step 1 — What the site uses
Step 2 — Site solar assumptions
Zero-bill tariff inputs (from your electricity bill)
Step 3 — Battery preferences
Confirm peak sun hours from BOM/PVWatts. Orientation factors computed for Darling Downs latitude (pvlib, relative to north 30°) — verify site-specific yield with PVWatts. Zero-bill assumes a flat-rate tariff; feed-in rates change annually and some retailers don't credit past $0 — take all tariff figures from a current bill. AS/NZS 4777 export rules apply to any grid-connected system.
PV String Fusing Calculator (AS/NZS 5033:2021)
Answers two questions for a PV array: do the strings need overcurrent protection, and what fuse size complies — per AS/NZS 5033:2021 Clauses 3.3.3–3.3.5 and Table 3.1. Enter the three module/array figures and the calculator does the rest.
Step 1 — Module & array (from the module datasheet)
Step 2 — Site factors (leave as-is for a typical grid-tied array)
Max series fuse rating is on the module datasheet (IEC 61730-2). Backfeed = current from BESS/PCE sources (0 for a typical grid-tied inverter). KI = 1 unless heightened irradiance applies (Appendix J). Use gPV fuses per IEC 60269-6 — circuit breakers are not recommended for string protection (Table 3.1 Note 1). Strings without DCUs assumed.
Add a line per load and pick its load group — demand factors per AS/NZS 3000:2018 Table C1 (domestic) or Table C2 (non-domestic). On a three-phase supply, allocate each load to a phase; the result is the heaviest loaded phase. Ratings in W, kW or A (230 V basis). Changing installation type or supply resets the lines.
Add loads above.
Counting (Table C1 notes): track = 2 points/m; sockets above 2.3 m and permanently connected appliances ≤150 W count as lighting points; a double outlet = 2 points; incandescent at 60 W minimum, discharge at full load incl. ballast. 15 A outlets add 10 A, 20 A outlets add 15 A (both installed = 15 A total). Heating and cooling both installed — enter the larger only.
Blocks of units: lighting and 10 A sockets are calculated automatically from the unit count; count-based lines take the number of units equipped. EV charging: 100% (single or 2–5 units/phase), 90% (6–20), 75% (21+). Non-domestic: welders entered as assessed current (Paragraph C2.5.2); X-ray at 50% of the largest unit. Demand may alternatively be determined by assessment, measurement or limitation (Cl 2.2.2 / 1.6.3). Need it certified? Talk to STILL LEC.
From preliminary numbers to certified design
These tools get you to a defensible first answer. When the project needs certified maximum demand assessments, cable schedules, protection studies, switchboard design or a licensed contractor to build it — STILL LEC delivers the full package, engineered and certified in-house from the Darling Downs.
