3-Phase Load Calculation Made Easy And Professional
Step 1: Learn The Basic Formula For 3-Phase Power
The formula for 3-phase power is really simple. It is 3-phase power equals 1.732 times the line voltage times the times the power factor.The 3-phase power is measured in watts.
The line voltage is measured in volts.
The current is measured in amps.
The power factor is a number between 0.8 and 1.
The number 1.732 is the root of 3.
Step 2: Rearrange The Formula To Find The Current
To find the current we need to rearrange the formula.So the current equals the 3-phase power divided by 1.732 times the line voltage times the power factor.
Step 3: Lets Do An Example Calculation
Lets say the total load is 10 kW which's 10000 watts.The voltage is 400 volts for a 3-phase system.
The power factor is 0.9.
We can calculate the current.
The formula becomes the current equals 10000 divided by 1.732 times 400 times 0.9.
The result is the current is approximately equal to 16 amps.
Step 4: Calculate The Breaker Size
To calculate the breaker size we need to add a safety factor.The safety factor is 125 percent.
So the breaker size is the times 1.25.
For our example this is 16 times 1.25 which equals 20 amps.
We should select a breaker that's either 20A or 25A and it should be a 3-pole breaker.
Step 5: Quick Reference Table For 3-Phase 400V Systems
Here is a reference table for different loads and their corresponding currents:| Load in kW | Current in A |
| 5 kW | approximately 8 A |
| 10 kW | approximately 16 A |
| 15 kW | approximately 24 A |
20 kW | approximately 32 A |
| 30 kW | approximately 48 A |
Step 6: Important Notes To Remember
When working with 3-phase systems always consider the power factor of the 3-phase system.Make sure to balance the load across all three phases of the 3-phase system.
Use 3-pole breakers for protection of the 3-phase system.
Select the cable size as it is very important for the 3-phase system.
For motors consider the starting current of the motors in the 3-phase system.
Step 7: Using Excel Formula For 3-Phase Calculation
The Excel formula for 3-phase calculation is really simple.It is the watts divided by 1.732 times the voltage times the power factor times 1.25.
For example it is 10000 divided by 1.732 times 400 times 0.9 times 1.25.
Final Tip
3-phase systems are more efficient, for loads.They are used for motors and industrial applications.
They require balancing and protection of the 3-phase system.
