NZ Electrical Calculators Guide
Quick electrical calculations compliant with AS/NZS 3000
In one sentence: WireWrite ships six free NZ electrical calculators — cable sizer, maximum demand, voltage drop, circuit check, earth fault loop impedance and solar string — all AS/NZS 3000 / 3008 / 5033 compliant and free to use without sign-up at wirewrite.co.nz/calculator.
Cable Sizer — AS/NZS 3008
Pick your circuit type, enter length and load, and get the recommended cable size with a voltage drop check in a single pass.
Maximum Demand — AS/NZS 3000 Tables C1/C2/C7
Calculate total maximum demand for domestic or non-domestic installations. Pre-loaded with NZ typical loads and diversity factors, recommends a main switch rating.
Voltage Drop — AS/NZS 3000 Clause 3.6.2
Shows pass/fail against the flat 5% NZ limit. Calculates the maximum length and maximum load that will keep you compliant.
Circuit Check
Verify an existing circuit is compliant. Enter cable size, breaker, length and load — get an instant pass/fail with specific checks against each AS/NZS 3000 limit.
Earth Fault Loop Impedance — AS/NZS 3000 Appendix B
Check measured or calculated Zs against AS/NZS 3000 Paragraph B4.5 maximum values. MCB Types B, C and D with the 80% rule and prospective fault current.
Solar String Sizing — AS/NZS 5033 / 4777.1
Calculate min/max modules per string with temperature correction, MPPT voltage window, and AS/NZS 5033 / 4777.1 system voltage limits.
Ohm’s Law
Solve for voltage, current, resistance or power given any two values. Quick V = IR and P = VI cross-check from anywhere in the wizard.
Disclaimer: All calculations are guidance only. Always verify results against AS/NZS 3000 / 3008 / 5033 and use professional judgement before commissioning any installation or issuing a Certificate of Compliance.
Frequently asked
Are the WireWrite NZ calculators free?
Yes. All six calculators (cable sizer, maximum demand, voltage drop, circuit check, earth fault loop impedance and solar string) are free to use with no sign-up. They are independent of the certificate platform and do not require a paid WireWrite subscription.
Which standard do the NZ calculators use?
Cable sizing uses AS/NZS 3008.1.1:2017 current-carrying capacity tables. Voltage drop applies the AS/NZS 3000 Clause 3.6.2 flat 5% limit. Maximum demand follows AS/NZS 3000 Tables C1, C2 and C7 for domestic and non-domestic installations. Solar string sizing uses AS/NZS 5033:2021 Table 4.1 cold-Voc factors. Earth fault loop impedance is checked against AS/NZS 3000 Appendix B (Paragraph B4.5).
What does the Cable Sizer calculate?
The Cable Sizer recommends a cable size for a given circuit type, length and load. It checks both current-carrying capacity (AS/NZS 3008.1.1) and voltage drop in a single pass and warns if a smaller cable would breach either limit. Typical results: 2.5mm² for 16/20A power circuits, 4mm² for 25-32A, 6mm² for an EV charger.
Does the Maximum Demand tool handle non-domestic installations?
Yes. The Maximum Demand calculator covers both domestic (Table C1) and non-domestic (Tables C2 and C7) installations. It pre-loads typical load values and diversity factors, lets you adjust per circuit, and recommends a main switch rating from the total.
How does the Earth Fault calculator work?
Enter the measured or calculated Zs for the circuit, the protective device type and rating, and the calculator returns a pass or fail against the AS/NZS 3000 Appendix B disconnection-time requirements. It supports MCB Types B, C and D with their corresponding Ia values, applies the 80% rule for measured impedance, and shows the resulting prospective fault current.
Can I use the calculator results to issue a CoC?
The calculators are guidance tools. The values they produce inform your design and verification but you remain responsible for the final compliance decision. Always cross-check critical results against the AS/NZS 3000 / 3008 / 5033 standards directly and apply professional judgement before commissioning an installation or issuing a Certificate of Compliance.
Do the calculators work on a phone in the field?
Yes. The calculators are responsive and work in any mobile browser. They do not require sign-in, so you can open wirewrite.co.nz/calculator on site without unlocking a paid account. The wider WireWrite app also installs as a Progressive Web App on Android and iOS for offline access to your saved drafts.
Use the WireWrite calculators in your full workflow
Issue compliant CoC, ESC and RoI certificates with the same standards data behind every calculation. 30-day free trial, no card.