How To Calculate Cable Sizes

Percentage Drop: $$% = \frac14.6415 \times 100 = 3.51%$$

For DC and single-phase AC circuits, the cross-sectional area ($A$) of the conductor is calculated using the following formula derived from Ohm's Law:

$1.5 , mm^2$, $2.5 , mm^2$, $4 , mm^2$, $6 , mm^2$, $10 , mm^2$, $16 , mm^2$, $25 , mm^2$, $35 , mm^2$, $50 , mm^2$, $70 , mm^2$, $95 , mm^2$, $120 , mm^2$, $150 , mm^2$, $185 , mm^2$, $240 , mm^2$. how to calculate cable sizes

Note: For Single Phase, remove the $\sqrt3$.

PVC-insulated copper, clipped to wall (method C), ambient 35°C, no grouping, length 40m. Percentage Drop: $$% = \frac14

Calculate the full load current of the circuit.

| Current (A) | Copper mm² (PVC) | Max length @ 3% drop, 230V | |-------------|------------------|-----------------------------| | Up to 16 | 1.5 | 25 m | | 16–25 | 2.5 | 30 m | | 25–32 | 4 | 40 m | | 32–45 | 6 | 55 m | | 45–60 | 10 | 70 m | Calculate the full load current of the circuit

This is the most common reason for increasing cable size. As current flows through a cable, resistance causes a drop in voltage. Standards usually limit this to for lighting and 5% for power.

Finally, you must ensure that in the event of a short circuit, the "fault current" is high enough to trip the breaker instantly. This involves checking the resistance of the cable (impedance). If the cable is too thin or too long, the breaker might not trip fast enough to prevent a fire. Summary Checklist Find ( Ibcap I sub b Pick a Breaker ( Incap I sub n Apply Correction Factors for heat/grouping. Pick a Cable Cross-Sectional Area ( mm2m m squared Check Voltage Drop limits. Ensure the Earth Path is safe.

If the cross-sectional area calculated here is larger than the area selected in Step 2, you must use the larger size.