Long cable runs lose voltage. Work out the volt drop and percentage drop for a run and check it against the 5% recommended in AS/NZS 3000.
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Start free trialVoltage drop rises with cable length and current, and falls as conductor size increases. A long run at high current needs a bigger cable to stay within limits.
Single-phase drop uses a factor of 2 (active plus return); three-phase balanced loads use √3. The tool applies the right factor for the system you pick.
AS/NZS 3000 recommends total voltage drop from the point of supply to any point in the installation stays within 5%. Over that, uprate the cable.
AS/NZS 3000 recommends that voltage drop between the point of supply and any point in the electrical installation does not exceed 5% of the nominal voltage. Some designers split this — for example allowing a portion for submains and the rest for final subcircuits — but 5% total is the general benchmark.
It depends on the current, the cable run length, the conductor’s cross-sectional area and its resistivity. This tool uses Vd = k × L × I × ρ ÷ A, where k is 2 for single phase or √3 for three phase. It’s a resistance-based estimate; precise design uses the mV/A/m figures from AS/NZS 3008.
Excessive voltage drop means equipment receives less than its rated voltage, causing motors to run hot, lights to dim, and controls to misbehave. It also wastes energy as heat in the cable. Keeping drop within limits protects both performance and safety.
It’s a useful indicative check, but formal cable design must use the current-carrying capacity and voltage-drop tables in AS/NZS 3008, allowing for installation method, grouping, ambient temperature and derating. Always verify with the standards and a licensed electrician.
This calculator is an indicative engineering aid using approximate resistivity values, not a substitute for design to AS/NZS 3000 and AS/NZS 3008. Cable selection must also account for current-carrying capacity, derating and installation conditions, and must be verified by a licensed electrician.
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