5.2 kW Cable 380 V Section Calculator (mm²)
Use this professional calculator to estimate the current, voltage drop, and recommended conductor size for a 5.2 kW three-phase load on a 380 V system. Adjust cable length, material, power factor, efficiency, and allowable voltage drop to obtain a practical cable section in mm².
Calculator
Voltage Drop Chart
This chart compares expected voltage drop for common cable sections, helping you understand why a mathematically possible section may still be upgraded to the next practical standard size.
Expert Guide: 5.2 kW Cable 380 V Calcul Section mm²
When people search for 5 2 kw cable 380 v calcul section mm, they usually want one thing: a reliable way to choose the right conductor size for a 5.2 kW load connected to a 380 V supply. In practice, that means converting power into current, checking the effect of cable length, accounting for conductor material, and limiting voltage drop to a sensible value. Although the request sounds simple, a correct answer depends on several electrical assumptions. A 5.2 kW motor at 380 V three-phase does not behave exactly the same as a 5.2 kW resistive heater, and a cable installed in free air does not have the same performance as one buried or grouped in conduit with other conductors.
The calculator above is designed to provide a practical starting point. It estimates current using power, line voltage, power factor, and efficiency. It then calculates the theoretical conductor section needed to stay within the selected voltage-drop limit. Finally, it rounds up to a standard cable size, because cables are not purchased in arbitrary decimal values like 2.73 mm². Instead, common standard sizes include 1.5, 2.5, 4, 6, 10, 16, and 25 mm².
Why cable section matters
The section of a cable, expressed in square millimeters, directly affects three major things:
- Current-carrying capacity: a larger section can carry more current without overheating.
- Voltage drop: a larger section reduces conductor resistance and therefore reduces the voltage lost along the cable run.
- Energy efficiency and reliability: undersized conductors waste power as heat and can shorten equipment life.
For a 5.2 kW load on 380 V, the current is often modest enough that ampacity alone might suggest a small cable, but voltage drop can still push the required size upward, especially on longer runs. That is why a professional cable calculation never relies on power alone.
Core formula used for a 380 V three-phase system
For three-phase AC systems, line current is estimated from active power using:
I = P / (√3 × V × cos φ × η)
Where:
- I = current in amperes
- P = power in watts
- V = line voltage in volts
- cos φ = power factor
- η = efficiency
If we use a typical motor-like assumption of 5.2 kW, 380 V, power factor 0.85, and efficiency 0.90, the current is approximately 10.3 A. That current is not high for copper conductors, but if the cable run is long, the voltage drop becomes the real design constraint.
Voltage-drop formula for cable section
For a three-phase circuit, a common engineering approximation for conductor section is:
S = (√3 × ρ × L × I) / ΔU
Where:
- S = conductor section in mm²
- ρ = resistivity in ohm·mm²/m
- L = one-way cable length in meters
- I = load current in amperes
- ΔU = allowable voltage drop in volts
For copper, designers often use a resistivity near 0.0175 ohm·mm²/m. For aluminum, a typical value is 0.0285 ohm·mm²/m. If the allowable drop is 3% on 380 V, then the maximum drop is 11.4 V. This means the same 5.2 kW load may be acceptable on a 2.5 mm² copper cable at a short distance, but require 4 mm² or even 6 mm² if the cable is long or the installation needs a stronger safety margin.
Typical result for a 5.2 kW load at 380 V
For many real-world installations, a 5.2 kW three-phase load at 380 V with a moderate run length of 20 to 30 meters often lands in the range of 2.5 mm² to 4 mm² copper, depending on power factor, efficiency, and selected voltage-drop limit. If the load is a motor with startup demand, or if the cable is grouped with other loaded circuits, the final practical selection may increase to 4 mm² or 6 mm² to improve thermal headroom and system stability.
| Scenario | Power | Voltage | Power Factor | Efficiency | Estimated Current |
|---|---|---|---|---|---|
| Three-phase motor, efficient | 5.2 kW | 380 V | 0.90 | 0.92 | 9.55 A |
| Three-phase motor, typical | 5.2 kW | 380 V | 0.85 | 0.90 | 10.33 A |
| Three-phase motor, lower PF | 5.2 kW | 380 V | 0.80 | 0.88 | 11.33 A |
| Near-resistive load | 5.2 kW | 380 V | 1.00 | 1.00 | 7.90 A |
The table shows why assumptions matter. At the same 5.2 kW and 380 V, current can vary from roughly 7.9 A to more than 11 A depending on load type. A user who simply divides 5200 by 380 will get the wrong answer for a three-phase system. The current is lower than a single-phase system because the power is shared across three phases.
Copper versus aluminum
Material choice has a major effect on section size. Copper has lower resistivity and better mechanical strength in smaller sections, so it is usually preferred for compact installations, control panels, and shorter building runs. Aluminum is lighter and often more economical in larger feeders, but it typically needs a larger section to achieve the same voltage drop and current-carrying performance.
| Property | Copper | Aluminum | Design Impact |
|---|---|---|---|
| Typical resistivity at 20°C | 0.0175 ohm·mm²/m | 0.0285 ohm·mm²/m | Aluminum usually needs about 1.6 times more section for similar drop. |
| Relative conductivity | About 100% benchmark | About 61% of copper | Copper reaches target performance with smaller conductors. |
| Weight | Higher | Lower | Aluminum can reduce weight on larger power runs. |
| Common use | Panels, machinery, building circuits | Larger feeders, utility style runs | Selection depends on installation environment and terminations. |
What section is usually chosen in practice?
For a 5.2 kW load at 380 V, the theoretical voltage-drop calculation may produce a section smaller than what field electricians finally install. That is normal. In practical design, the next standard size is selected, and then checked against:
- continuous operating current,
- ambient temperature correction,
- grouping or bundling correction,
- insulation type and conductor temperature rating,
- circuit breaker or fuse coordination,
- motor starting conditions,
- future expansion margin.
As a rule of thumb, if your calculation suggests 2.2 mm², you do not buy 2.2 mm². You move to 2.5 mm². If that result looks tight once derating is applied, you move to 4 mm². For industrial motors, engineers frequently choose the next size above the minimum when there is any uncertainty about load profile, startup duty, or environmental temperature.
How cable length changes the answer
Length is often the decisive factor in a cable sizing calculation. A short run of 10 meters and a long run of 80 meters can have completely different recommended sections, even if the power and voltage remain the same. Because voltage drop is proportional to current and length, doubling the cable run roughly doubles the drop for the same cable size.
Consider a typical 5.2 kW, 380 V, three-phase motor current around 10.3 A with a 3% maximum voltage drop. On a short run, 1.5 mm² or 2.5 mm² may look mathematically feasible. On longer distances, the design quickly moves to 4 mm², 6 mm², or 10 mm². This is one of the main reasons cable calculators are so useful: they reveal that a seemingly small load can still need a surprisingly robust conductor because of installation geometry rather than pure amperage.
Recommended design process
- Identify whether the load is single-phase or three-phase.
- Confirm the actual running power in kW.
- Use a realistic power factor and efficiency for motors or drives.
- Measure the one-way length accurately.
- Select the conductor material.
- Set an allowable voltage-drop target, often 3% for branch circuits or lower where starting torque is important.
- Calculate the theoretical minimum section.
- Round up to the next standard cable size.
- Verify ampacity and installation derating using the applicable code or manufacturer table.
- Check protective device coordination and fault performance.
Important standards and authority references
Any online calculator should be treated as an estimating tool, not a substitute for code compliance. Always verify the final conductor size against your local regulations and recognized engineering references. The following sources are useful starting points:
- OSHA electrical safety resources
- U.S. Department of Energy guidance on electric motors and efficiency
- Educational engineering reference on voltage drop
Common mistakes when sizing a 5.2 kW cable at 380 V
- Ignoring power factor and efficiency: this underestimates current for motor loads.
- Using single-phase formulas on a three-phase system: this produces incorrect current values.
- Forgetting cable length: short and long runs cannot share the same assumption.
- Choosing the exact calculated area: always move to the next standard size.
- Overlooking derating: grouped cables, heat, and conduit fill can significantly reduce capacity.
- Ignoring motor starting conditions: voltage drop during startup can cause nuisance trips and poor starting torque.
Final practical conclusion
If you are estimating 5 2 kw cable 380 v calcul section mm, the result for a typical three-phase installation usually falls into a modest conductor range, often 2.5 mm² to 4 mm² copper for common distances, with larger sections required as the run increases or design conditions become more demanding. The right answer is never based on one number alone. It comes from combining current calculation, voltage-drop limitation, standard size selection, and local code checks.
The calculator on this page gives you a fast, practical estimate. It is especially useful when comparing copper and aluminum, testing multiple lengths, or seeing how a tighter voltage-drop target changes the required section. If your installation involves critical motors, high ambient temperatures, grouped conductors, or long cable runs, treat the estimate as the first step and perform a full code-based verification before final installation.