Cable Capacitance Calculator

Accurate capacitance calculations for single core and multi-core cables

Cable Capacitance Calculator

Compliant with IEC Standards for Cable Design

Results:

Capacitance: 0.00 μF/km

Capacitance per meter: 0.00 nF/m

Capacitive Reactance (50Hz): 0.00 Ω·km

Capacitive Reactance (60Hz): 0.00 Ω·km

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How to Use the Calculator

Single Core Cable

  1. Select "Single Core Cable"
  2. Choose insulation material
  3. Enter conductor diameter (d)
  4. Enter diameter over insulation (D)
  5. Verify relative permittivity

Multi-Core Cable

  1. Select "Multi-Core Cable"
  2. Choose insulation material
  3. Enter individual conductor diameter
  4. Enter diameter over core insulation
  5. Results show per-core capacitance

Material Selection

  1. PVC: Most common, higher capacitance
  2. XLPE: Lower capacitance, better performance
  3. Butyl/Silicone: Specialized applications
  4. Temperature affects permittivity

How to Calculate Cable Capacitance

Use these practical checkpoints to collect data, apply the IEC-friendly formula, and interpret the result with confidence.

Step 1: Define Cable Geometry

Measure the conductor diameter (d) over the copper and the diameter over the insulation (D) in millimeters with a calibrated micrometer.

  • Log(D/d) is very sensitive to these measurements, so round each value to at least two decimal places before using the calculator.

Step 2: Select Dielectric Constant

Choose the insulation material from the drop-down so the proper relative permittivity (εr) is used.

  • XLPE (2.3) always yields a lower capacitance than PVC (3.3) under identical geometry because of its smaller permittivity.

Step 3: Apply the Standard Formula

Plug the values into the logarithmic equation to obtain capacitance per kilometer and per meter simultaneously.

  • C = εr / (18 × log(D/d)) µF/km is the base expression for a single-core shielded cable.

Step 4: Convert and Compare

The calculator reports µF/km and nF/m automatically, so you can compare specs from different manufacturers without rework.

  • Remember that 1 µF/km = 1 nF/m, a handy conversion when cross-checking data sheets.

Step 5: Consider Multi-Core Behavior

When analyzing three-core cables with individual screens, evaluate the mutual capacitance between phases as well as the phase-to-earth capacitance.

  • Use the same formula for each screened core, then sum or average depending on whether you are checking charging current or unbalance.

Step 6: Validate Against Limits

Compare the calculated capacitance with relay, inverter, or VFD limits to ensure charging current and reactive power stay manageable.

  • Xc = 1 / (2π f C) quickly reveals how higher capacitance drives the capacitive reactance down at 50/60 Hz.

Cable Capacitance Chart

Reference values for typical MV and LV constructions help verify whether your inputs are realistic.

Cable Type d (mm) D (mm) εr Capacitance (µF/km) Capacitance (nF/m)
1C 25 mm² PVC 5.6 9.5 3.3 0.40 0.40
1C 95 mm² XLPE 11.0 18.5 2.3 0.28 0.28
3C 50 mm² XLPE (screened) 8.0 15.0 2.3 0.33 0.33
1C 185 mm² EPR 15.3 25.5 2.8 0.31 0.31
1C 22 AWG Shielded Pair 0.65 1.80 3.0 0.62 0.62

Cable Capacitance FAQs

Clear answers to the most searched capacitance questions.

How to calculate capacitance in cable?

Determine conductor diameter d, insulation diameter D, and the dielectric constant of the insulation. Substitute them into the same logarithmic formula IEC handbooks recommend for shielded cables.

  • C = εr / (18 × log(D/d)) µF/km then convert to nF/m by noting 1 µF/km equals 1 nF/m.
What is the capacitance per meter of cable?

Per-meter capacitance is the same numeric value as the per-kilometer result expressed in µF/km. Simply report the answer in nF/m for easier comparison with instrumentation and communications cable datasheets.

What is capacitance in a cable?

Cable capacitance describes how much electric charge accumulates between the conductor and screen for a given voltage. Higher capacitance increases charging current, reactive power, and stress on connected converters.

What is the capacitance of 22 AWG wire?

A typical shielded 22 AWG instrumentation pair with PVC insulation and foil shield exhibits roughly 60 nF/km (0.06 µF/km), although values can range from 40 nF/km to 80 nF/km depending on insulation thickness.

What is the formula for the capacitance of a coaxial cable?

Coaxial cables follow the same logarithmic relationship but often use natural log form: C = (2πεr&epsilon0) / ln(D/d). The calculator’s base-10 version is algebraically equivalent once you transform the log term.

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