How To Calculate The Cable Size [extra Quality] 🎯
If you only size for thermal limits, long runs will disappoint you. A motor at the end of a 300-meter cable might receive 200V instead of 230V. It will draw more current, overheat, and fail early. Voltage drop ( ( V_drop = I \times R_cable \times length ) ) is not just a nuisance—it is an economic and performance constraint.
You need to consider:
Real-world conditions reduce a cable's ability to dissipate heat, meaning its capacity must be adjusted. how to calculate the cable size
| Cable Size (mm²) | Approx. AWG Equivalent | Maximum Current (Amps) | Typical Application | | :--- | :--- | :--- | :--- | | | 18 AWG | 10 – 15 A | Lighting Circuits | | 1.5 mm² | 16 AWG | 15 – 20 A | Lighting, Radial Sockets (Light load) | | 2.5 mm² | 14 AWG | 20 – 25 A | Ring Mains, Sockets, Water Heaters | | 4.0 mm² | 12 AWG | 25 – 32 A | Cookers, Showers, Sub-mains | | 6.0 mm² | 10 AWG | 32 – 40 A | Electric Showers, Sub-mains | | 10.0 mm² | 8 AWG | 40 – 50 A | Main Distribution Boards | | 16.0 mm² | 6 AWG | 50 – 63 A | High Capacity Sub-mains | If you only size for thermal limits, long
I=P3Ă—VĂ—PFcap I equals the fraction with numerator cap P and denominator the square root of 3 end-root cross cap V cross cap P cap F end-fraction Where: = Power in Watts. Voltage drop ( ( V_drop = I \times
The formula is slightly different: $$I = \fracPV \times \sqrt3 \times \textPower Factor$$
Ideally, voltage drop should be kept below 3% for lighting and 5% for power circuits.
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