Understanding Voltage Drop in Copper Wires for 240 Volt Systems

When working with electrical systems, particularly those running at high voltages such as 240 volts, it is crucial to understand the concept of voltage drop. Voltage drop is a significant factor that affects the performance and efficiency of electrical installations, especially in larger gauge copper wires. This article will delve into the factors that contribute to voltage drop, the role of current, and how to calculate it for a 1/0 copper wire running 200 feet at 240 volts.

Defining Voltage Drop

Voltage drop is the reduction in electrical potential that occurs along a length of wire due to the resistance of the wire itself. The voltage drop can be calculated using the formula:

Voltage Drop (mV) R x I x L

Where:

R Resistance per unit length (milliohms per foot) I Current (in Amperes) L Length of the wire (in feet)

Factors Contributing to Voltage Drop

The factors that contribute to voltage drop include the type of conductor, its gauge, the length of the circuit, and the load current. In this section, we will focus on the specific case of a 1/0 copper wire running 200 feet at 240 volts.

Calculating Voltage Drop for 1/0 Copper Wire

First, it is important to know the current that the wire is carrying. The voltage drop is measured in millivolts (mV) per ampere per foot (A/ft). To determine the voltage drop, we need to know the wire's resistance per foot at the operating temperature. For a 1/0 copper wire with XHHW insulation:

Resistance per foot at 25°C (77°F) 0.100 milliohms/ft Resistance per foot at 75°C (167°F) 0.122 milliohms/ft

Assuming the wire is operating at 90°C (194°F), we can use the resistance at 75°C for our calculations. Let's assume a full rated load of 170 amps.

Calculation

Resistance of 170 Amps flowing through 200 feet of 1/0 copper wire:

200 feet x 0.122 milliohms/ft 24.4 milliohms

Then, the voltage drop:

0.0244 x 170 4.148 Volts

Temperature and Wire Resistance

It is worth noting that temperature significantly affects the resistance of the wire. Copper has a lower temperature coefficient compared to aluminum, which is why aluminum wires are generally rated for lower current at the same gauge. For aluminum wire of the same gauge (1/0 XHHW building wire), the resistance per foot at 75°C is:

Resistance per foot at 20°C (68°F) 0.165 milliohms/ft Resistance per foot at 75°C (167°F) 0.200 milliohms/ft

Assuming the wire is operating at 135 amps:

200 feet x 0.200 milliohms/ft 40 milliohms

Then, the voltage drop:

0.040 x 135 5.4 Volts

The Importance of Current

It's important to highlight the impact of current on voltage drop. If there is no current, there is no voltage drop. This is a fundamental principle of electrical circuits. Here's a simple example:

A 10 AWG copper wire with a diameter of 5.3 mm2 has a resistance of 0.0032 Ohms per meter. If you have 20 meters of 2 of this wire with a current of 10 A, the voltage drop is 1.3 Volts. The voltage of the system does not affect the voltage drop if there is no current.

Conclusion

In summary, the voltage drop in a 1/0 copper wire running 200 feet at 240 volts is highly dependent on the current flowing through the wire. Understanding and correctly calculating voltage drop is crucial for designing and maintaining efficient electrical systems. Always consult the wire manufacturer's charts for the expected voltage drop based on the wire size and operating temperature.

Additional Resources

For more detailed information on voltage drop calculations, refer to the following resources:

Voltage Drop Calculator by K/E Electric Supply Corporation Voltage Drop Calculator by Speer Wires