Calculating Voltage Drop for 200HP Motor at 480V

In summary, a question was asked about determining voltage drop in a scenario with a 200HP motor located 300 ft. away from the starter at 480V. A formula was provided for calculating %VD(3phase) using a value of 12 for copper and the Full Load Amp of 240A. The only missing piece was the circular mil, which can be found in the American Wire Gauge chart.
  • #1
vptran84
46
0
Hi,

I was wondering if anyone can help me figure out how much voltage drop is happening in this particular scenario.

Here is my work:

Given 200HP motor at 480V that is 300 ft. away from the starter.

%VD(3phase) = [12(1.73)(300ft.)(240A)]/[(Circular mil) * (480V)] x100

I use 12 for copper, and with 200HP the Full Load Amp is 240A.

I have no idea where i can get the circular mil. Can someone please help me. I know that it's somewhere in the NEC.

thanks.
 
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  • #3


Hi there,

Calculating voltage drop for a 200HP motor at 480V can be done using the following formula:

%VD = [(2 x K x I x L) / (CM x V)] x 100

Where:
- K is the specific resistance of the conductor material (copper = 12.9)
- I is the full load current of the motor (240A)
- L is the length of the conductor (300 ft)
- CM is the circular mils of the conductor (can be found in NEC Table 8)
- V is the voltage (480V)

Using this formula, we can calculate the voltage drop as follows:

%VD = [(2 x 12.9 x 240 x 300) / (250000 x 480)] x 100
%VD = 0.01275%

This means that there is a very small voltage drop of 0.01275% in this scenario. It is important to note that this calculation assumes a balanced three-phase system and does not take into account any other factors such as temperature, type of conductor, or any additional loads on the circuit.

I hope this helps you with your calculation. If you have any further questions, please feel free to ask. Good luck!
 

1. What is the formula for calculating voltage drop for a 200HP motor at 480V?

The formula for calculating voltage drop is VD = (I x L x R) / 1000, where VD is voltage drop in volts, I is the current in amps, L is the length of the wire in feet, and R is the resistance of the wire in ohms per thousand feet.

2. How do I determine the current and resistance values for the formula?

The current value can be found by dividing the power (in watts) of the motor by the voltage (in volts). In this case, the current would be 416.67 amps (200 HP = 149200 watts / 480V). The resistance value can be obtained from a wire size chart or by measuring the wire's gauge and consulting a wire gauge table.

3. What is the length of the wire that should be used for the calculation?

The length of the wire used in the formula should be the total distance from the power source to the motor.

4. Can I use the same formula for different motor sizes and voltages?

The formula for calculating voltage drop can be used for any size motor at any voltage, as long as the current and resistance values are known. It is important to note that the wire gauge used may vary depending on the motor size and voltage, so consulting a wire gauge table is recommended.

5. What is an acceptable voltage drop for a 200HP motor at 480V?

Generally, a voltage drop of no more than 3% is considered acceptable for a 200HP motor at 480V. This means that the voltage at the motor should not drop more than 14.4V (480V x 0.03) from the voltage at the power source. A larger voltage drop can result in decreased motor performance and efficiency.

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