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Voltage Drop Check

Voltage drop and % for a chosen cable size.

Electrical

Inputs (SI units)

Results

Voltage drop
3.24 V (0.54 %)
Receiving-end voltage
596.76 V
I²R power loss
38.86 W (0.54 % of transmitted power)
Loop resistance
0.26989 Ω
Minimum cable size to pass
2.5 mm²
Current size already passes
✓ PASS — Voltage drop (0.54 %) is within the allowable 2 % limit.

Engineering Recommendations

  • →Current cable size (6 mm²) meets the 2% allowable drop.
  • →Re-verify at maximum expected operating current and worst-case conductor temperature.
  • →Engineering-grade preliminary calculation. Final design must be verified against project-specific site conditions, manufacturer datasheets, applicable standards and utility requirements.

Detailed Calculation Log

Allowable drop 2 % vs actual 0.54 %.

Save & Load Project

Designs are stored privately in this browser — nothing is uploaded.

Engineering Formula

  • DC / 1-φ: V_d = 2 × ρ × L × I / A
  • 3-φ: V_d = √3 × ρ × L × I / A
  • % drop = V_d / V × 100

Drop is IR loss on the loop. For balanced 3-φ systems only line-to-neutral drop matters — hence the √3 factor.

Step-by-step Calculation

  1. 1.Operating currentI12 A
  2. 2.Resistivity at operating temperatureρ20 × (1 + α×(T−20))0.0202 Ω·mm²/m
  3. 3.One-way conductor resistanceρT × L / (A × parallel)0.13495 Ω
  4. 4.Loop (DC) resistance2 × R_one-way0.26989 Ω
  5. 5.Voltage dropI × R_loop3.24 V
  6. 6.Voltage drop percentageVdrop / V × 1000.54 %
  7. 7.I²R power lossI² × R_loop38.86 W
  8. 8.Loss as % of transmitted powerPloss / (V×I) × 1000.54 %
  9. 9.Receiving-end voltageV − Vdrop596.76 V
  10. 10.Minimum area to meet allowable drop2ρLI / (V×VDallow×parallel)1.62 mm² → 2.5 mm² standard

How to use this calculator: Voltage Drop Check

Voltage drop and % for a chosen cable size. The example below is calculated by this page's real engine from the displayed inputs.

  1. 1Confirm that the Voltage Drop Check matches the quantity or design check you need.
  2. 2Enter Source voltage, Operating current, and One-way length using the units printed beside each field.
  3. 3Select the applicable Conductor material options; these choices change the calculation method or factors.
  4. 4Calculate, then follow the substituted equations in the worked example and compare the result with any stated limit.
  5. 5Read the assumptions, warnings and cited references before using the result for a financial, medical or engineering decision.

Input guide and example values

Use values from the same measurement basis and time period. Conditional fields appear only when the related option is selected.

InputExample valueWhy it matters
Source voltage600 VMeasured or known source voltage used by the calculation engine.
Operating current12 AMeasured or known operating current used by the calculation engine.
One-way length40 mMeasured or known one-way length used by the calculation engine.
Cable cross-section6 mm²Measured or known cable cross-section used by the calculation engine.
Parallel conductors1 -Measured or known parallel conductors used by the calculation engine.
Conductor materialCopperSelect the option that matches the real installation or scenario.
Conductor operating temperature65 °CMeasured or known conductor operating temperature used by the calculation engine.
Allowable voltage drop2 %Measured or known allowable voltage drop used by the calculation engine.

Formula inputs & variables for Voltage Drop Check

These are the named quantities used by this calculator. When the source formula does not define a mathematical symbol, OneCalcApp keeps the real input label instead of inventing one.

Variable / inputUnitMeaning in this calculation
Source voltageVMeasured or known source voltage used by the calculation engine.
Operating currentAMeasured or known operating current used by the calculation engine.
One-way lengthmMeasured or known one-way length used by the calculation engine.
Cable cross-sectionmm²Measured or known cable cross-section used by the calculation engine.
Parallel conductors-Measured or known parallel conductors used by the calculation engine.
Conductor material—Select the option that matches the real installation or scenario.
Conductor operating temperature°CMeasured or known conductor operating temperature used by the calculation engine.
Allowable voltage drop%Measured or known allowable voltage drop used by the calculation engine.

How the Voltage Drop Check works

The Voltage Drop Check uses Source voltage, Operating current, One-way length, Cable cross-section, Parallel conductors, Conductor material, Conductor operating temperature, and Allowable voltage drop to calculate Voltage drop, Receiving-end voltage, I²R power loss, Loop resistance, and Minimum cable size to pass. Its engine applies DC / 1-φ: V_d = 2 × ρ × L × I / A; the worked values below come from that same live calculation rather than a separately typed example.

With Source voltage 600 V, Operating current 12 A, One-way length 40 m, Cable cross-section 6 mm², Parallel conductors 1 -, Conductor material Copper, Conductor operating temperature 65 °C, and Allowable voltage drop 2 %, the main worked-example result is Voltage drop = 3.24 V (0.54 %).

How each Voltage Drop Check input is used

Source voltage

The Voltage Drop Check worked example uses Source voltage = 600 V. This value is passed directly into the calculation, with an allowed minimum 5.

Operating current

The Voltage Drop Check worked example uses Operating current = 12 A. This value is passed directly into the calculation, with an allowed minimum 0.1.

One-way length

The Voltage Drop Check worked example uses One-way length = 40 m. This value is passed directly into the calculation, with an allowed minimum 0.1.

Cable cross-section

The Voltage Drop Check worked example uses Cable cross-section = 6 mm². This value is passed directly into the calculation, with an allowed minimum 0.5.

Parallel conductors

The Voltage Drop Check worked example uses Parallel conductors = 1 -. This value is passed directly into the calculation, with an allowed minimum 1.

Conductor material

The Voltage Drop Check worked example selects “Copper”. Available choices include Copper and Aluminium. This selection may change the method or factor used by the engine, so choose the option that matches the real case.

Conductor operating temperature

The Voltage Drop Check worked example uses Conductor operating temperature = 65 °C. This value is passed directly into the calculation, with an allowed minimum -20 and maximum 120.

Allowable voltage drop

The Voltage Drop Check worked example uses Allowable voltage drop = 2 %. This value is passed directly into the calculation, with an allowed minimum 0.2 and maximum 10.

Voltage Drop Check formulas and result interpretation

Formula 1: relationship used

In the Voltage Drop Check, DC / 1-φ: V_d = 2 × ρ × L × I / A. The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Formula 2: relationship used

In the Voltage Drop Check, 3-φ: V_d = √3 × ρ × L × I / A. The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Formula 3: relationship used

In the Voltage Drop Check, % drop = V_d / V × 100. The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Voltage drop

For the displayed Voltage Drop Check worked example, Voltage drop is 3.24 V (0.54 %). Verify Source voltage, Operating current, and One-way length and their units before relying on this output.

Receiving-end voltage

For the displayed Voltage Drop Check worked example, Receiving-end voltage is 596.76 V. Verify Source voltage, Operating current, and One-way length and their units before relying on this output.

I²R power loss

For the displayed Voltage Drop Check worked example, I²R power loss is 38.86 W (0.54 % of transmitted power). Verify Source voltage, Operating current, and One-way length and their units before relying on this output.

Loop resistance

For the displayed Voltage Drop Check worked example, Loop resistance is 0.26989 Ω. Verify Source voltage, Operating current, and One-way length and their units before relying on this output.

Minimum cable size to pass

For the displayed Voltage Drop Check worked example, Minimum cable size to pass is 2.5 mm². Current size already passes Verify Source voltage, Operating current, and One-way length and their units before relying on this output.

Voltage Drop Check accuracy, checks and limitations

  • Voltage Drop Check units check: confirm Source voltage (V), Operating current (A), One-way length (m), Cable cross-section (mm²), Parallel conductors (-), Conductor material, Conductor operating temperature (°C), and Allowable voltage drop (%) before calculating.
  • Voltage Drop Check result check: compare Voltage drop, Receiving-end voltage, I²R power loss, Loop resistance, and Minimum cable size to pass with the substituted formula steps and the displayed rounding precision.
  • Voltage Drop Check: Use this result for preliminary design and cross-checking. Confirm the applicable code edition, manufacturer data, site conditions and qualified-engineer approval before final design or installation.

Understanding the result

Read the main result together with supporting checks, assumptions, limits and intermediate values.

For a manual check, repeat the first equation, confirm the units and change one input at a time.

Common mistakes when using Voltage Drop Check

  • Do not mix units for Source voltage (V), Operating current (A), One-way length (m). A unit mismatch changes the input magnitude even when the typed number looks reasonable.
  • Do not leave Conductor material on the default choice unless that choice matches the real scenario; the selected option can change the calculation path or factor.
  • Do not replace the displayed DC / 1-φ: V_d = 2 × ρ × L × I / A relationship with a different convention without also changing the underlying assumptions; compare like-for-like methods when checking the result.
  • Do not treat Voltage drop = 3.24 V (0.54 %) from the worked example as a universal answer. It belongs to the displayed example inputs and must be recalculated for the actual case.

When the Voltage Drop Check is useful

Voltage Drop Check is designed for cases where Source voltage, Operating current, One-way length, Cable cross-section are known and you need Voltage drop, Receiving-end voltage, I²R power loss. The page keeps the live calculator, calculation method and worked example together so the result can be checked instead of treated as a black-box number.

Use the calculator for the scope described by its inputs and notes. The displayed method is DC / 1-φ: V_d = 2 × ρ × L × I / A. If the real project or decision needs factors that are not represented here, treat the result as an estimate and add the missing checks separately.

Source voltage and Operating current: what changes the answer

The worked example uses Source voltage = 600 V, Operating current = 12 A, One-way length = 40 m, Cable cross-section = 6 mm². With those values, Voltage drop is 3.24 V (0.54 %). Changing an input should be interpreted according to that field's unit, range, option and hint rather than by the number alone.

For this calculator, the main input roles are: Source voltage (V): Measured or known source voltage used by the calculation engine. Operating current (A): Measured or known operating current used by the calculation engine. One-way length (m): Measured or known one-way length used by the calculation engine. Cable cross-section (mm²): Measured or known cable cross-section used by the calculation engine.

How to sanity-check a Voltage Drop Check result

Start by confirming the entered values and units, then compare the substituted working with the displayed formula or calculation steps. Pay particular attention to Voltage drop, because it is the first worked-example output shown by the live engine.

Finally, compare the result with the assumptions, warnings and related calculators on this page. A nearby calculator can be useful as a cross-check when it measures the same workflow from a different input or output direction.

Next logical calculator

Continue with 100 & 200 Amp Service Wire Size Calculator

Useful next check because both tools use Conductor material, while 100 & 200 Amp Service Wire Size Calculator answers a different part of the same workflow.

Open 100 & 200 Amp Service Wire Size Calculator

Standards, source trail and limitations

References show the method used. Check the current local edition, amendments and project specification before a regulated decision.

Design Assumptions

  • • Resistive drop only; reactance ignored (short LV cables).
  • • 20 °C reference — use DC Cable Sizing for temp correction.

Engineering Tips

  • ◆Lighting circuits: ≤ 3%.
  • ◆Power circuits: ≤ 5% total from source (per NEC 210.19).

Warnings

  • ▲Drop > 5% causes motor heating and PV clipping.

Standards & References

IEC 60364-5-52IS 3043NEC 210.19

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