10 Free Electrical and Solar Calculators Every NZ Electrician Should Bookmark

Most electricians end up with the same handful of tools bookmarked, or half-remembered from a reg book, or scattered across two or three different apps: a cable sizing table here, a volt drop calculator there, a maximum demand spreadsheet from a job three years ago. We built these into CertMate as free, no-login calculators, because they're the tools we reach for ourselves, every week, and there was no reason to make anyone sign up just to use them.

1. Mains & Submain Cable Selection

Finds the smallest compliant cable for consumer mains or a submain, checking both current-carrying capacity and voltage drop against AS/NZS 3008.1.2 together, rather than sizing on one and hoping the other holds up.

2. Voltage Drop

Checks any cable run, single or three phase, against the 5% limit, and works out the maximum run length for a given load. The calculator every sparky ends up needing at least once a week.

3. Earth Fault Loop Impedance

Checks a measured Zs directly against the maximum allowed for the breaker in question, so there's no need to go hunting through a tabulated maximum-Zs table on site.

4. Ohm's Law

Enter any two of voltage, current, resistance or power and get the other two instantly. Simple, but it's the calculator that ends up saving the most time in a normal working week.

5. Three-Phase Converter

Converts kW, kVA and amps between single and three phase, with power factor included, for commercial and light industrial jobs where getting this wrong on paper is an expensive mistake to make on site.

6. Maximum Demand

Works out maximum demand for a single dwelling or a block of units under AS/NZS 3000:2018 Table C1, building a load schedule item by item rather than one flat guess. Read the full guide on how Table C1 works if you want the detail behind it.

7. Solar String Sizing & DC:AC Ratio

Works out the minimum and maximum panels per string with temperature-corrected Voc and Vmp, checked against the inverter, its MPPT window and the AS/NZS 5033 domestic or commercial d.c. limit. Then lay the strings out on the inverter's inputs to check the DC:AC ratio, the input current and short-circuit limits, and each string's length.

8. Solar DC Voltage Drop

Checks PV d.c. cable volt drop, string cable and array cable together, against the AS/NZS 5033 5% limit and its 3% recommendation, with the conductor resistance corrected for how hot the cable runs on a roof.

9. DC Isolator & Fuse Rating

Works out whether string fuses are needed and the window their rating has to fall in, the current every PV cable has to carry, the PV maximum voltage, and the current and voltage a d.c. isolator must be rated for at the right temperature, all from AS/NZS 5033.

10. AC Voltage Rise

Adds up the voltage rise from the point of supply to the inverter, cable by cable, against the AS/NZS 4777.1 2% limit, and checks every cable can carry the inverter's full rated current, even with an export limit.

Why we built these into CertMate rather than a separate site

Because they don't need to live somewhere else. The same tools you use to plan a job sit right next to the certificates and test sheets you issue once it's done, no separate login, no separate app to remember.

Browse the full set on the Electrical Calculators page, free, no login required. When you're ready for the certificates and test sheets that go with them, start a free trial.