MV Conductor Voltage Drop Calculator and Formula

An MV conductor voltage drop calculator estimates the voltage lost along a medium-voltage cable from its length, load current, conductor resistance and reactance, and power factor. Enter consistent electrical units and select single- or three-phase service; the result is an approximate drop in volts and as a percentage of system voltage, not a cable or equipment safety approval.

Formula

This calculator uses an approximate AC voltage-drop formula, resolving the conductor’s resistance and reactance according to the load power factor:

ΔV = I × L × (R × PF + X × √(1 − PF²)) × K

• ΔV is the estimated voltage drop in volts.
• I is load current in amperes.
• L is one-way circuit length in kilometres, converted from the entered metres.
• R is conductor AC resistance in ohms per kilometre.
• X is conductor reactance in ohms per kilometre.
• PF is the load power factor, from 0 to 1.
• K is 1 for the single-phase formula and approximately √3 for the balanced three-phase formula.

Voltage-drop percentage is 100 × ΔV divided by the entered system voltage. Estimated receiving voltage is system voltage minus the calculated drop. For three-phase systems, voltage is normally the line-to-line voltage and current is line current. The expression is an engineering approximation; detailed studies may use complex impedance and account for operating conditions along the circuit.

Worked Example

Using the calculator’s defaults: 11,000 V, 100 A, 1,000 m, resistance 0.2 Ω/km, reactance 0.1 Ω/km, power factor 0.9, and three-phase service:

1. Convert the length: 1,000 m ÷ 1,000 = 1 km.
2. Calculate the reactive term: √(1 − 0.9²) = √0.19 ≈ 0.43589.
3. Calculate the impedance component: (0.2 × 0.9) + (0.1 × 0.43589) ≈ 0.22359 Ω/km.
4. Apply the three-phase factor: ΔV = 100 × 1 × 0.22359 × 1.73205 ≈ 38.73 V.
5. Percentage drop = 100 × 38.73 ÷ 11,000 ≈ 0.35%.
6. Estimated receiving voltage = 11,000 − 38.73 = 10,961.27 V.

The displayed results are 38.73 V, 0.35%, and 10,961.27 V. The numbers are illustrative; the resistance and reactance must represent the actual cable and relevant operating conditions for a useful estimate.

What to Enter and Where the Data Comes From

MV commonly means medium voltage, but voltage ranges and terminology vary by country and utility. The calculator does not decide whether a particular system qualifies as MV. Use the nominal voltage appropriate to the circuit and the same voltage basis as the calculated result: for the three-phase option, generally line-to-line voltage.

• Length: enter the one-way route length in metres. Do not enter the total of all three phase conductors. The formula’s phase factor handles the balanced three-phase relationship.
• Current: use the expected load current in amperes for the operating case being assessed, not automatically the conductor’s maximum rating.
• Resistance and reactance: obtain values for the conductor, size, construction, and applicable frequency from reliable cable data or engineering calculations. Enter ohms per kilometre.
• Power factor: enter the load power factor as a decimal: 0.9 means 90%, not 90. A leading or unusual load may need a more detailed phasor treatment than this simplified formula.
• System type: choose single-phase or balanced three-phase. An unbalanced circuit or a system with significant neutral current is not represented by the standard three-phase factor.

If data is supplied in ohms per 1,000 feet, convert it before entering it: 1,000 feet is 0.3048 km, so multiply the ohms-per-1,000-foot value by about 3.28084 to obtain ohms per kilometre. Keep length and impedance units aligned; mixing feet with ohms per kilometre can create a large error.

How to Interpret the Result

The voltage-drop result is the estimated difference between sending-end and receiving-end voltage under the entered conditions. A smaller percentage means a smaller drop relative to nominal voltage, but it does not by itself establish that the design is acceptable. Project criteria, equipment requirements, operating scenarios, and applicable standards must be checked separately by qualified personnel.

The estimate changes with current and length: doubling either approximately doubles the calculated drop if the other inputs remain constant. Resistance and reactance both matter in AC circuits. The power-factor term changes their contribution; treating the cable as resistance-only can be misleading, especially over long distances or where reactance is significant.

Voltage drop is not the same as conductor ampacity, short-circuit withstand, insulation coordination, or protection performance. A cable may show a modest calculated drop and still be unsuitable for other reasons. Conversely, a drop result alone cannot prescribe a conductor size or breaker.

Accuracy, Assumptions, and Common Errors

The formula treats the circuit as having a uniform impedance and assumes the entered current and power factor describe the relevant load. It does not model cable temperature changes, conductor skin or proximity effects beyond whatever is reflected in the supplied resistance, joints, parallel runs, detailed load distribution, harmonics, transients, or the complete network source impedance. For long MV feeders or consequential design decisions, a qualified engineer may need a more complete load-flow or network analysis.

• Do not confuse kilovolts with volts: 11 kV must be entered as 11,000 V.
• Do not enter power factor as a percentage; use 0.90 rather than 90.
• Do not double the length for a three-phase cable. The three-phase factor is already included.
• Do not use conductor resistance at an arbitrary temperature when the operating temperature matters. Verify what temperature the source value represents.
• Do not round intermediate values aggressively. The calculator rounds displayed results, not the underlying calculation.

The calculator allows a zero power factor mathematically, but its simplified treatment of phase angle does not distinguish leading from lagging power factor. It also reports a negative receiving voltage if an extreme input produces a drop greater than the nominal voltage; that signals an unrealistic or out-of-scope case, not a physically meaningful operating prediction.

Frequently Asked Questions

What formula is used for three-phase MV voltage drop?
For a balanced three-phase circuit, this calculator uses ΔV ≈ √3 × I × L × (R × PF + X × √(1 − PF²)), with length in kilometres and R and X in ohms per kilometre.

Should I enter line-to-line or phase voltage?
For the three-phase option, enter line-to-line system voltage when calculating the percentage drop and estimated receiving voltage. The drop formula returns a line-to-line voltage difference for a balanced system.

Do I enter one-way or round-trip cable length?
Enter one-way route length. Do not double it for three-phase service. For single-phase circuits, the selected formula uses a factor of 1 and assumes the entered length corresponds to the circuit-length convention required by that approximation; confirm the convention used by your cable data or design method.

Where can I find cable resistance and reactance?
Use manufacturer or engineering data for the actual conductor and installation conditions. Check the units, frequency, conductor temperature, and whether the resistance is AC or DC; the calculator cannot infer these values from cable size alone.

Does this calculator tell me what cable size to install?
No. It estimates voltage drop for values you provide. Cable selection also involves ampacity, fault performance, insulation, installation conditions, protection, and project requirements, so it requires a complete engineering assessment.

Related

• Robot Gripper Selection: Vacuum, Soft & Parallel Jaw
• NVMe Data Recovery: What Works and What Doesn’t
• PoE Device Class vs Type: What It Means

in v | System voltage | V | 11000 | 0 | 1000000
in i | Load current | A | 100 | 0 | 1000000
in l | One-way cable length | m | 1000 | 0 | 1000000
in r | Conductor resistance | ohm/km | 0.2 | 0 | 1000
in x | Conductor reactance | ohm/km | 0.1 | 0 | 1000
in pf | Power factor | - | 0.9 | 0 | 1
sel ph | System type | Single-phase=1, Three-phase=1.7320508075688772
out drop | Voltage drop | V | i * (l / 1000) * (r * pf + x * sqrt(1 - pf ^ 2)) * ph | 2
out pct | Voltage drop | % | 100 * drop / v | 2
out recv | Estimated receiving voltage | V | v - drop | 2