Cable selection for a 7.5 KW 3 Ph motor

 Cable Size Calculation

1. Basic Formula (3 Phase Load)

Current (A)=Power (kw) * 1000/( sqrt 3 * Voltage* PF* Efficiency)

2. Example - Motor Cable Size

→ Given

Motor Power = 7.5kW

Voltage = 415V

Power Factor = 0.8

Efficiency =0.9

3. Step 1: Calculate Current

Current = 7500 /(1.732 * 415 * 0.8 * 0.9)

→ Current = 14A - 15A

→ Current = 14-15 A

3. Select Cable Size (Copper)

Current (A)

Copper Cable Size

→ For 15 A motor → 2.5 sqmm Cu cable

Up to 10 A-1.5 sqmm

Up to 16 A-2.5 sqmm

Up to 25 A+4 sq mm

4. Aluminium Cable Selection

(Practically site 4 sqmm लेते है for safety) Aluminium cable approx 1.5 times copper size 2.5 sqmm C u Right arrow 4 sqmm Al

Up to 35 A-6 sqmm

Up to 50 A-10 sq mm

4 sqmm Cu 6 sqmm Al

For 15 A motor→25 sqmm Cu cable (Practically site u 4 sqmm ad for

5. Voltage Drop Check (Important)

Voltage Dcrop ( V)= √3* ILR (प्रेसने L = length in km)

6. Quick Thumb Rules (Site Use)

1 HP motor 1.5-2.5 sqmm Cu

5 HP motor 4 sqmm Cu

Technician Practical Tips:

7.5 HP motor → 4-6 sqmm Cu

Long cable = Size increase 외

10 HP motor 6 sqmm Cu

Underground cable Derating factor apply

High temperature- Bigger size required