Low-Voltage Cable Sizing: Short-Circuit, Ampacity & Voltage-Drop Essentials
Power Projects 
Learn how to size LV cables by evaluating short-circuit capacity, current-carrying capability, and voltage drop for safe, efficient installations.
Cable Sizing Calculation – Low Voltage
INPUT DATA
| System voltage | 415 V |
| Type of Insulation | XLPE |
| Type of conductor | Copper |
| Maximum Ambient air temperature | 40° |
| Ground temperature | 30° |
| Continuous temperature of the cable | 90° |
| Maximum short circuit temperature of the cable | 250° |
| Load details | |
| Power Rating of motor | 90 kW |
| Source Voltage | 415 V |
| Efficiency | 0.9 |
| Power factor | 0.85 |
| Cable details | |
| Length | 120 m |
| Resistance of the conductor (95mm2) | 0.247 ohm/km (As per Cable Catalogue) |
| Reactance of the conductor (95mm2) | 0.0734 ohm/km (As per Cable Catalogue) |
CABLE SIZING CALCULATION CRITERIA
The minimum cross-section of LV voltage cables shall be calculated based on the below methods:
- Short circuit current capacity
- Current carrying capacity
- Voltage drop of cable
1. Short circuit current capacity
This criterion defines the minimum cross-section required for the cable.
| A | = | Cable cross-section area in Sq. mm |
| Isc | = | Short circuit current |
| K | = | Constant, 143 for XLPE Cu. Cable |
| t | = | Duration of short-circuit in seconds |
The fault current at 415V is 40kA and the duration t is considered to be 0.1 based on relay delay time and breaker opening time.
The next nearest available cable size will be,
Categories: : Load flow
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