Voltage Drop Calculator
Estimate wire voltage loss, percentage drop, receiving-end voltage and a suggested conductor size for DC, single-phase AC and three-phase AC circuits.
Your calculation results
Calculation details
| System | — |
|---|---|
| Conductor | — |
| One-way length | — |
| Calculated load current | — |
| Estimated conductor resistance at entered temperature | — |
| Target voltage drop | — |
| Approximate wire loss as a percentage of input power | — |
Suggested wire size for your target
This suggestion considers estimated voltage drop only. It does not certify ampacity, short-circuit performance, terminal ratings, installation suitability, or code compliance.
How to use this voltage drop calculator
- Choose DC, single-phase AC, or three-phase AC.
- Enter the nominal circuit voltage and either load current or real power.
- Enter the one-way distance from the supply to the load and select the unit.
- Choose copper or aluminum and select the conductor cross-sectional area.
- For AC circuits, enter the load power factor if known. Reactance can be included when reliable cable data is available.
- Set your design voltage-drop target and calculate the result.
- Review the result and check conductor ampacity and applicable electrical rules separately.
Voltage drop formulas used
DC two-wire circuit: Vd = 2 × I × L × R
Single-phase AC approximation: Vd = 2 × I × L × (R × PF + X × sinφ)
Three-phase AC approximation: Vd = √3 × I × L × (R × PF + X × sinφ)
Here, L is one-way length in kilometres for the AC expressions when R and X are in ohms per kilometre; R is estimated conductor resistance per kilometre at the entered temperature; X is the entered reactance per kilometre; PF is power factor; and φ is the angle whose cosine equals PF. The DC calculation uses one-way length in metres and resistance per metre.
Why does voltage drop matter?
Excessive voltage drop can cause equipment to receive less voltage than expected. Depending on the equipment and load, this may contribute to poor performance, reduced starting torque, nuisance shutdowns, or additional conductor heating. The acceptable limit depends on the circuit, equipment, design requirements, and governing electrical code.
Voltage drop is not an ampacity calculation
A conductor can meet a voltage-drop target and still be unsuitable for the load. Before choosing a final wire size, check ampacity, conductor insulation rating, ambient temperature, grouping and bundling, overcurrent protection, terminal temperature ratings, installation method, and applicable local requirements.
Frequently asked questions
Does cable length mean one-way or round-trip distance?
Enter one-way distance. The DC and single-phase formulas account for the return path; the three-phase formula uses the three-phase approximation.
Which is better for reducing voltage drop: copper or aluminum?
For the same cross-sectional area and conditions, copper generally has lower resistance. Aluminum may require a larger cross-section to achieve a comparable voltage-drop result, and its terminations must be suitable for aluminum conductors.
Why does a larger wire reduce voltage drop?
A larger conductor generally has lower electrical resistance, so less voltage is lost when current flows through it.
Can I use this for motor circuits?
You can estimate running voltage drop if the load data is appropriate. Motor starting current can be much higher than running current, so starting conditions need a separate assessment.
Is 3% voltage drop always the legal limit?
No. A 3% target is commonly used as a design reference in some contexts, but it is not a universal legal limit for every circuit. Check the applicable code, project specification, and equipment requirements.
Is this calculator code-certified?
No. It provides an engineering estimate using simplified resistance-based formulas. Verify the result with applicable code requirements and reliable cable manufacturer data before installation.
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| Voltage Drop Calculator |
Voltage Drop Calculator: Electrical Wire Voltage Loss Guide
Voltage drop is the reduction in electrical voltage that occurs as current travels through a wire or cable. Every conductor has resistance, so some voltage is lost as electrical energy travels from the power source to the connected equipment.
A voltage drop calculator helps estimate this loss using the circuit voltage, load current, conductor size, wire material, circuit length, and electrical system type. It can help electricians, electrical students, contractors, and DIY users compare wire sizes before planning an installation.
What Causes Voltage Drop?
Voltage drop mainly depends on the resistance of the conductor and the current flowing through it. Longer wires generally have greater resistance, while larger conductors generally have lower resistance.
The main factors are:
- Wire length: A longer circuit usually produces greater voltage drop.
- Load current: Higher current increases the voltage lost across the conductor.
- Conductor size: Smaller conductors typically have higher resistance.
- Wire material: Copper and aluminum have different electrical resistance.
- Temperature: Conductor resistance generally increases as temperature rises.
- Circuit configuration: Single-phase, three-phase, and DC circuits use different calculation approaches.
Voltage Drop Formula
For a simple DC circuit, or a single-phase circuit using an appropriate resistance approximation,
