Voltage Drop Calculator
Calculate voltage drop in electrical circuits for proper wire sizing and electrical system design. Ensure safe and efficient electrical installations.
Circuit Parameters
Voltage Drop Results
Calculation Details
Wire Specifications
Recommendations
How to Use
Select your circuit type (DC or AC) and enter the system voltage.
Enter the current (amperage) that will flow through the circuit.
Input the one-way distance from source to load.
Choose wire material and size, or use the helper to find recommended sizes.
Review results and recommendations for safe electrical installation.
Understanding Voltage Drop
What is Voltage Drop?
Voltage drop is the reduction in voltage that occurs when electrical current flows through a conductor. It's caused by the resistance of the wire and can affect the performance of electrical equipment.
Formula: V = I × R
- V = Voltage drop (volts)
- I = Current (amperes)
- R = Resistance (ohms)
Acceptable Voltage Drop Limits
NEC Guidelines
- • Branch circuits: 3% maximum
- • Feeders: 3% maximum
- • Combined: 5% maximum
- • Motor circuits: 5% maximum
Low Voltage DC
- • 12V systems: 3% (0.36V)
- • 24V systems: 3% (0.72V)
- • Critical loads: 2% maximum
- • LED lighting: 5% acceptable
Factors Affecting Voltage Drop
Wire Properties
- • Wire size (AWG)
- • Material (copper vs aluminum)
- • Length of run
- • Temperature rating
Circuit Conditions
- • Current load
- • Operating temperature
- • AC vs DC current
- • Power factor (AC)
Installation
- • Conduit fill
- • Ambient temperature
- • Conductor bundling
- • Connection quality
Applications
Residential
- • Home electrical circuits
- • Outdoor lighting
- • Pool and spa wiring
- • Garage and workshop
- • Solar panel systems
Commercial
- • Office building wiring
- • Retail store circuits
- • Warehouse lighting
- • HVAC systems
- • Emergency lighting
Industrial
- • Motor control circuits
- • Manufacturing equipment
- • Control panel wiring
- • Instrumentation
- • Power distribution
Example Calculations
Residential Circuit
Wire: 12 AWG copper
Resistance: 1.93 Ω/1000ft
Calculation: (100ft × 2 × 1.93/1000) × 15A = 5.79V drop
Percentage: 5.79V ÷ 120V = 4.8%
DC Solar System
Wire: 10 AWG copper
Resistance: 1.21 Ω/1000ft
Calculation: (50ft × 2 × 1.21/1000) × 20A = 2.42V drop
Percentage: 2.42V ÷ 12V = 20.2% (too high!)
Frequently Asked Questions
Why is voltage drop important?
Excessive voltage drop can cause equipment malfunction, reduced efficiency, overheating, and safety hazards. It's especially critical for motors, lighting, and sensitive electronic equipment.
How do I reduce voltage drop?
Use larger wire sizes, shorter cable runs, higher voltage systems, or multiple parallel conductors. Copper has lower resistance than aluminum for the same size.
What's the difference between voltage drop and voltage regulation?
Voltage drop is the loss in a conductor, while voltage regulation is the ability of a power source to maintain constant voltage under varying loads. Both affect system performance.
Do I need to consider temperature effects?
Yes, conductor resistance increases with temperature. High ambient temperatures or current loading can significantly increase resistance and voltage drop.
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