Eaton Voltage Drop Calculator: Formula and Limits

An Eaton voltage drop calculator estimates the voltage lost along a circuit from its current, conductor length, wire size, material, and system type. This page calculates the basic single-phase or direct-current estimate when you enter those values; it does not replace Eaton’s product-specific tools or a qualified electrical design review.

Formula

The calculator uses a simplified resistance-based formula for a copper-like or aluminum-like conductor, depending on the resistivity value entered. It treats the listed length as the one-way distance from source to load.

• Voltage drop, volts: ΔV = K × I × L × ρ ÷ A ÷ 1,000.
• Percentage drop: ΔV% = 100 × ΔV ÷ V.
• Estimated load-end voltage: Vload = V − ΔV.

Here, ΔV is voltage drop in volts; K is the circuit factor (2 for DC or single-phase, 1.732 for balanced three-phase); I is current in amperes; L is one-way conductor length in feet; ρ is conductor resistivity in ohm-circular-mil per foot; A is conductor area in circular mils; and V is source voltage in volts. The area field is expressed in kcmil, or thousands of circular mils, hence the division by 1,000. Enter 10.4 as an approximate copper resistivity or 17 as an approximate aluminum value when using this simplified model. Actual resistivity varies with temperature and material.

This is a basic resistive estimate, not a complete AC impedance calculation. The three-phase factor assumes a balanced system and line-to-line voltage. For a detailed calculation, conductor impedance, power factor, operating temperature, conduit or cable arrangement, and the applicable electrical code or design criteria may matter.

Worked Example

Using the block’s defaults—120 V source, 20 A load, 100 ft one-way length, 12.9 kcmil conductor area, 10.4 ohm-cmil/ft resistivity, and DC or single-phase—the calculation is:

1. Convert area to circular mils: 12.9 × 1,000 = 12,900 cmil.
2. Calculate the round-trip factor for this circuit: K = 2.
3. Voltage drop = 2 × 20 × 100 × 10.4 ÷ 12.9 ÷ 1,000 = 3.2248 V, or 3.22 V.
4. Percentage drop = 100 × 3.2248 ÷ 120 = 2.6873%, or 2.69%.
5. Estimated load-end voltage = 120 − 3.2248 = 116.7752 V, or 116.78 V.

The result is an estimate based on the inputs, not a statement that the selected wire is suitable for a particular installation.

What Eaton’s Calculator Means

“Eaton voltage drop calculator” can refer to a tool or resource associated with Eaton, a manufacturer of electrical equipment. Availability and features may change, so consult Eaton’s current official website or product documentation if you need its own calculator, a particular application, or a product-specific design resource. The general calculation on this page explains the underlying estimate; it should not be presented as Eaton’s official tool.

Voltage drop is the reduction in electrical potential between a source and a load while current flows. A long run, high current, small conductor area, or higher-resistance material increases the drop. Increasing conductor area or shortening the run reduces it in this simplified model. The voltage actually present at the load can also be affected by supply variation, connections, temperature, and other circuit components.

How to Use the Estimate

• Source voltage: Enter the circuit’s nominal voltage, such as 120 V or 240 V. For balanced three-phase, use the line-to-line voltage.
• Current: Use the expected load current in amperes. A circuit’s breaker rating is not automatically its operating current.
• Length: Enter the one-way distance from the source to the load in feet. Do not enter the total out-and-back conductor length; the formula applies its circuit factor separately.
• Area: Enter the conductor’s area in kcmil. If you have a wire gauge rather than an area, use a reliable wire-size reference to obtain its area before calculating.
• Resistivity: Select a value appropriate to the conductor material and assumptions. A higher resistivity produces a higher estimated drop.
• Circuit type: Choose DC or single-phase for the factor of 2, or balanced three-phase for 1.732.

Length is a frequent source of error. For example, a 100 ft one-way single-phase run has about 200 ft of current path in the simple loop model. Entering 200 ft into this calculator and also applying its factor of 2 would count that distance twice.

Limits, Units, and Common Mistakes

This calculator accepts feet, volts, amperes, kcmil, and the specified resistivity units. If your measurements are metric, convert length from metres to feet (1 m is about 3.28084 ft) before entering it. Do not enter square millimetres directly as kcmil; convert the conductor area using a dependable unit conversion. Mixing wire-size conventions or resistivity units can create a result that looks plausible but is wrong.

The formula is most useful as a first-pass estimate for a simple run. It does not determine ampacity, acceptable conductor size, breaker or fuse selection, grounding, short-circuit performance, or compliance with electrical codes. It also does not account precisely for AC reactance or power factor. In a three-phase circuit with substantial imbalance, a single balanced-system factor is not a complete model.

Do not treat a low percentage result as proof that a design is safe. Wire selection and installation involve hazards and requirements beyond voltage drop. Have a qualified electrical professional verify conductor sizing, protective devices, installation conditions, and applicable rules. Eaton product documentation may provide additional information for particular equipment, but the relevant application and current documentation should be checked directly.

Frequently Asked Questions

Does Eaton have an official voltage drop calculator?
Tools and documentation can change. Check Eaton’s official website or the documentation for the specific equipment to confirm whether an official calculator is currently available. This page provides a general calculation, not an Eaton-branded tool.

Do I enter one-way or total wire length?
Enter one-way source-to-load distance. The formula’s factor of 2 accounts for the outgoing and return paths in DC and single-phase circuits.

How do I calculate voltage drop for three-phase power?
For a balanced three-phase estimate, select the three-phase factor, 1.732, and enter line-to-line source voltage. This simplified resistive formula does not cover every AC installation condition.

Can I enter wire gauge instead of kcmil?
No. The area field expects kcmil. Convert the gauge to conductor area using a trustworthy wire-size table, then enter that area.

Why is my real voltage drop different?
Actual conductor temperature, material, connections, load variation, AC impedance, power factor, and measurement conditions can all affect the result. The calculator uses idealized resistive assumptions.

Does this result tell me what wire size to install?
No. It estimates voltage drop only. A qualified professional must check conductor ampacity, protection, installation details, and applicable requirements before selecting or installing wiring.

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in v | Source voltage | V | 120 | 0.001
in i | Load current | A | 20 | 0
in l | One-way conductor length | ft | 100 | 0
in a | Conductor area | kcmil | 12.9 | 0.001
in r | Conductor resistivity | ohm-cmil/ft | 10.4 | 0.001
sel c | Circuit type | DC or single-phase=2, Three-phase=1.732
out drop | Voltage drop | V | c * i * l * r / a / 1000 | 2
out pct | Voltage drop | % | 100 * drop / v | 2
out end | Estimated load-end voltage | V | v - drop | 2