Formula For Cable Sizing | UPDATED – 2027 |

[ V_d = \frac\sqrt3 \times L \times I \times (R \cos\phi + X \sin\phi)1000 ]

Iz=InCg×Ca×Ci×Cfcap I sub z equals the fraction with numerator cap I sub n and denominator cap C sub g cross cap C sub a cross cap C sub i cross cap C sub f end-fraction Incap I sub n is the rating of the protective device, and factors represent derating for grouping ( Cgcap C sub g ), ambient temperature ( Cacap C sub a ), thermal insulation ( Cicap C sub i ), and frequency ( Cfcap C sub f 1. Calculate Load Current ( Ibcap I sub b

[ A = \fracIJ ]

When sizing a cable, follow this order:

It≥InCa×Cg×Ci×Cdcap I sub t is greater than or equal to the fraction with numerator cap I sub n and denominator cap C sub a cross cap C sub g cross cap C sub i cross cap C sub d end-fraction Incap I sub n : The rating of the circuit breaker/fuse. Cacap C sub a formula for cable sizing

Ensure: [ V_d,calculated \le 3% \text of V_nom \text (lighting) \quad \textor \quad 5% \text (power) ]

Download our free Cable Sizing Formula Cheat Sheet (PDF) — [Link to resource] [ V_d = \frac\sqrt3 \times L \times I

The standard single-phase and three-phase voltage drop formulas are:

The formula for Three-Phase voltage drop ($\Delta V$) is: formula for cable sizing

[ I_b = \fracP\sqrt3 \times V_L \times \cos\phi \quad \text(for 3-phase) ] [ I_b = \fracPV_P \times \cos\phi \quad \text(for single-phase) ]

$$I_t \geq \fracI_nC_a \times C_g \times C_i \times C_c$$