Cable Inductance Calculator

Example data table

Formula used

How to use this calculator

1. Select the cable configuration that matches your run.
2. Enter frequency and total route length.
3. Choose a frequency mode that fits your application.
4. Fill in the geometry inputs in your preferred units.
5. Press Calculate to view results above the form.
6. Use CSV or PDF exports for checklists and submittals.

Accurate inductance estimates help safer, quieter electrical installations everywhere.

Cable Inductance in Construction

Why inductance matters

Site feeders, temporary boards, hoists, and cranes all depend on cables carrying changing current. Inductance resists those changes, adding reactive impedance that influences voltage drop and equipment starting. Estimating inductance supports safer sizing, commissioning checks, and troubleshooting.

Common site layouts

Inductance is driven by conductor spacing and geometry. Widely separated conductors on trays typically have higher inductance than bundled multicore cable. Trefoil single-core routing often lowers inductance and reduces external magnetic fields. Flat three-phase spacing can raise inductance and increase interference near controls.

What this calculator estimates

This tool provides practical estimates for typical geometries: two-wire circuits, coax-like arrangements, and three-phase sets in trefoil or flat formation. It uses conductor radius, spacing, run length, and relative permeability to compute inductance per meter and total inductance.

Inputs you should measure

Enter conductor radius (or diameter/2), center-to-center spacing, and installed length. If the route includes significant ferromagnetic containment, inductance can rise; adjust the relative permeability only when you have reliable data. For three-phase, pick the installed arrangement to avoid misleading results.

Worked example

Consider a 50 m two-wire feeder with 5 mm radius conductors and 60 mm spacing in non-magnetic containment (μr = 1). Submit those values to obtain inductance per meter and total inductance. Multiply by angular frequency to estimate inductive reactance, then compare options such as reduced spacing or different routing.

Interpreting results

Higher total inductance means higher reactance at the same frequency, increasing reactive voltage drop and affecting motor or transformer energization on weak supplies. For variable-speed drives, inductance can moderate di/dt, but excessive inductance may worsen regulation and power factor.

Practical reduction tips

Keep outgoing and return conductors close together, use trefoil for single-core three-phase, avoid unnecessary separation on trays, and minimize loop area at joints and terminations. Where practical, select multicore cable and route phases together. Recheck values if the cable path changes during construction.

Example data snapshot

Documentation and reporting

Record the geometry, spacing, and calculated inductance in commissioning notes so later changes are traceable. If protective settings are sensitive, keep both the inductance and the derived reactance used in checks. When a circuit is rerouted or phases are split temporarily, recalculate and update the as-built file.

FAQs

1) Is this inductance value exact for every cable?

No. It’s an estimate based on geometry and assumptions. Manufacturer data, cable construction, and installation environment can shift results. Use it for planning and cross-checking, then validate against project specifications when available.

2) What spacing should I enter for multicore cable?

Internal spacing is not easy to measure. Prefer manufacturer inductance data. If you must estimate, use an equivalent center spacing based on the cable’s construction notes and treat the outcome as approximate.

3) Why does trefoil usually reduce inductance?

Trefoil keeps phase conductors close and symmetric, reducing loop area and balancing magnetic fields. That typically lowers inductance and external field strength compared with a wide flat arrangement.

4) How does inductance relate to voltage drop?

Inductance creates inductive reactance, which adds to circuit impedance. Under load, reactance contributes reactive voltage drop. Combine resistance and reactance to assess total drop and power-factor impacts.

5) What if the cable is in steel conduit or near steel?

Ferromagnetic materials can increase effective permeability and raise inductance. If you have credible permeability information, adjust μr. Otherwise, keep μr near 1 as a baseline and verify during detailed design.

6) Which frequency should I use for reactance checks?

Use the supply fundamental frequency for standard checks. For harmonics from drives or switching, evaluate reactance at the harmonic frequencies too, since reactance increases linearly with frequency.

7) Can higher inductance ever be beneficial?

Sometimes. More inductance can reduce di/dt and limit high-frequency current spikes. However, it can also worsen regulation and power factor, so assess the full system behavior.