Electrical

# Voltage Drop Calculator: Circuit Volt Loss Over Distance

This voltage drop calculator determines the voltage drop across a circuit, particularly useful for long wire runs. It computes the voltage drop based on input parameters like voltage, current, wire size, conductor type, and circuit distance. Additionally, it calculates the voltage at the load and the percentage voltage drop.

Voltage Drop Calculator

## Voltage Drop Calculator

This voltage drop calculator is provided for estimation purposes only and should not be considered professional advice. We are not liable for any inaccuracies or errors resulting from user input or application of the calculator's results. Users are responsible for verifying the output with a qualified professional and adhering to local codes and regulations.

## How to Calculate Voltage Drop

Voltage drop calculation is grounded in one of the most fundamental electrical engineering principles: Ohm’s Law. Ohm’s Law posits that the voltage difference across a conductor is directly proportional to the current flowing through it and the conductor’s total resistance.

Voltage drop is determined by multiplying the current and the resistance within the conductor. This concept has led to the derivation of a straightforward formula for computing the voltage drop in a conductor.

You can accurately determine the voltage drop for a specific circuit and select the appropriate wire gauge to ensure the drop remains within acceptable limits.

According to the National Electrical Code, the voltage drop in a feeder circuit should not exceed 5%, and in a branch circuit, it should be limited to 3% or less.

### Input Parameters:

Voltage: Enter the source voltage of the circuit.

• DC 12V, 24V, 48V
• Single-phase voltages are 115V or 120V
• Three-phase voltages are 208V, 230V, 240V, or 480V.

Amperes: Enter the maximum current (in amps) expected to flow through the circuit. For motor circuits, use the nameplate Full Load Amperage (FLA) multiplied by 1.25.

Wire Size: Select the wire size in American Wire Gauge (AWG) or kcmil.

Conductor: Choose between common conductor materials like Copper or Aluminum.

Distance: Input the one-way length of the wire in the circuit in feet.

### Key Information:

• Conductor Temperature: Calculations are based on a conductor temperature of 75°C.
• Source Reference: NFPA 70, National Electrical Code, Chapter 9, Table 8.

### Calculation Formulas:

#### Calculation Formulas:

Ohm’s Law: Voltage drop (Vd​) is calculated as Vd​=I×R, where I is current and R is resistance.

Single-Phase Circuits: Vd=(2×K×L×I)/Cm​

Three-Phase Circuits: Vd=(1.73×K×L×I)/Cm​

Where:

• Vd​ = Voltage Drop
• I = Current in Conductor (Amps)
• L = One-way Length of Circuit (Feet)
• Cm = Cross Sectional Area of Conductor (Circular Mils)
• K = Resistance in ohms of 1 circular mil foot of conductor (12.9 for Copper, 21.2 for Aluminum at 75°C)

## AWG chart

• The results are estimations and may vary based on wire condition, temperature, connector quality, etc.
• Voltage drop should ideally be less than 5% under full load for optimal performance.
• Voltage drop factors include wire material, size, length, and current carried.
• Ensure proper cable selection and adherence to bundling rules for accurate ampacity and voltage drop estimations.

### Tools and Resources:

• Circuit Distance Calculator: For determining the maximum circuit distance based on the desired voltage drop.
• Wire Size Calculator: To calculate the appropriate wire size for your circuit.
• Advanced Wire Size/Ampacity Calculator: For more detailed wire sizing and ampacity calculations.

Related tools:

Author

Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.