Choose an efficient cable size for appliances, tools, and chargers today safely. Factor in distance, phase, material, and voltage drop for confidence every time.
This calculator picks the smallest standard conductor size that satisfies both an ampacity check and a voltage drop check, using simplified resistive models.
Cable size controls heating and voltage drop. Undersized conductors run hot, waste energy, and can trip breakers or damage motors. A correctly sized cable keeps devices stable and improves safety for everyday circuits like heaters, pumps, ovens, and chargers.
The key input is current (amps). If you only know power, convert it using voltage, power factor, and efficiency. Single-phase current is based on V × PF × efficiency, while three-phase uses √3 × V × PF × efficiency. This step prevents “rule of thumb” errors when loads vary.
Real installations aren’t perfect. Connections age, ambient temperature changes, and loads can grow. A 10–30% margin is common for planning, especially when appliances may be upgraded later. This calculator applies your chosen margin to create a design current for selection.
Ampacity is the approximate current a conductor can carry without exceeding its temperature rating. In practice it must be derated for heat, grouping of multiple circuits, and restrictive routing like conduit or insulation. The correction factors in the form represent those effects, producing a required ampacity target.
Long runs create resistance, reducing the voltage at the load. Many households target 3% drop for branch circuits and 5% for longer feeders, but local rules vary. This tool checks a resistive drop model: 2 × I × L × (ρ/A) for single-phase and √3 × I × L × (ρ/A) for three-phase.
Copper has lower resistivity, so it typically needs a smaller cross-section for the same drop. Aluminum is lighter and often cheaper, but needs larger sizes, careful termination hardware, and good installation practice. For small conductors, verify local suitability and connector ratings before choosing aluminum.
Resistance rises with temperature. A conductor that runs warmer will drop more voltage and lose more power as heat. The calculator adjusts resistivity using a temperature coefficient, improving estimates when cables are in warm spaces like attics or near equipment.
The recommended size is the smallest standard cross-section meeting both ampacity and voltage drop checks with your assumptions. Treat the output as a starting point: confirm installation method, insulation rating, protective device sizing, and applicable wiring regulations. Download the CSV or PDF to document choices for maintenance and future changes.
The length input is one-way. The voltage drop formula internally accounts for the return path for single-phase circuits. For three-phase, it uses a standard line-to-line drop approximation based on conductor resistance.
Many users aim for about 3% for branch circuits and up to 5% for longer feeders, but requirements vary by country and application. Sensitive electronics and motors often benefit from lower drop targets.
They change the current for a given power. Lower power factor or efficiency means higher current, which increases heating and voltage drop. Enter realistic values for motors, compressors, and switch-mode power supplies.
No. It uses a resistive model for straightforward planning. Long runs, large conductors, or non-linear loads can introduce additional effects. For complex cases, consult design tables or an electrician.
Voltage drop grows linearly with length and current, but drops with conductor area. Past a certain length, meeting the drop limit becomes the dominant constraint, pushing the selection to larger standard sizes.
It depends on local rules and approved terminations. Aluminum typically requires larger sizes and careful connections to prevent loosening or oxidation issues. Always verify connector ratings, torque specs, and code acceptance.
The protective device must protect the conductor under the applicable rules. Cable size, installation method, and ambient conditions all matter. Use the result as guidance, then choose protection that meets local requirements.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.