How to Select Electrical Wire Size ?
Selecting the correct electrical wire size is essential for safety, performance, and compliance with electrical standards.
Here’s a complete guide on how to select electrical wire size for a specific load:
Key Factors to Consider
• Load Current (Amperes)
• Based on the total connected electrical load (Watts).
Formula:
Current (A)=Power (W) /(Voltage (V)×Power Factor (PF))
For resistive loads (like lights, heaters), PF ≈ 1.
Length of Cable Run
• Longer distances need thicker cables due to voltage drop.
Ambient Temperature
• High temperatures reduce cable current-carrying capacity.
Safety Standards & Codes
• Follow NEC, IEC, or local code for derating, conduit fill, etc.
Step-by-Step: How to Select Wire Size?
Step 1: Calculate Load Current
Step 2: Select Suitable Wire Gauge Values may vary depending on insulation type and installation method (Ex: conduit, air).
Voltage Drop Formula
Where:
L = Length (m)
I = Current (A)
R = Resistance (Ω/km) based on wire size
Target voltage drop: < 3% of system voltage
Tools You Can Use
• Online Cable Size Calculators
• NEC/IEC Wire Ampacity Tables
• Multimeter (to measure actual load)
• Clamp Meter (to measure current draw)
Tips
• Always round up the cable size (for safety).
• Consider future expansion of load.
• Factor in starting currents (motors, compressors).
• Use MCB/Breaker matching the cable’s ampacity.