An interactive underground duct bank ampacity calculator and layout tool for medium-voltage cable systems — a lightweight, one-time-purchase alternative to expensive seat-licensed ampacity software. Runs entirely in your browser — no install, no subscription, no internet connection required after download.

What it does

This duct bank sizing calculator and cable duct bank heat rise calculator lets you design the physical duct bank, place your cables, and get IEC 60287 ampacity calculator or Neher-McGrath calculator results — thermal, electrical, and short-circuit — all in one interactive session, with a to-scale section drawing generated automatically as you work.

• Click-to-paint cable layout — pick a circuit and phase, tap ducts to fill them. Trefoil, triplex, single-phase-per-duct, spares, and empty ducts all supported.

• Multiple duct banks, side by side — independent rows/columns, spacing, stagger, cover, and backfill per bank, with automatic gap dimensioning between banks.

• Underground duct bank thermal resistivity calculator built in — full backfill/soil model with concrete envelope, fluidized thermal backfill, sand, or native soil, plus surface layers (asphalt over engineered fill over native soil) with depth-weighted effective thermal resistivity.

• Cable build library — conductor (1/0 AWG–1500 kcmil, Cu or Al), conductor screen, insulation, insulation screen, metallic shield (tape or wire), and jacket, each with configurable thickness and thermal resistivity.

• Rigorous thermal network — layered T1 (conductor→screen), T3 (jacket), and T4 external resistance (in-duct, duct wall, self and mutual heating by the image method), with IEC duct-bank geometric correction (r_b) per envelope shape.

• Circulating sheath current calculator built in — screen circulating currents from a real impedance-matrix solve across all bonded sheaths, circuits, and banks simultaneously, not a simplified per-cable approximation. Trefoil/triplex proximity effects and circulating-current collapse are captured automatically.

• Two calculation engines — IEC 60287-1-1 / 2-1 vs Neher-McGrath, with load-factor loss adjustment, selectable per project.

• Cable short circuit rating (IEC 60949) — conductor and screen adiabatic short-circuit withstand ratings at your specified fault duration and final temperature.

• Electrical properties per circuit — capacitance, charging current, inductance, reactance, surge impedance, and dielectric stress at the conductor and insulation screens.

• Heat-map visualization — see hottest conductors at a glance, colored against ambient/rated/over-temperature bands.

• Duct bank drawing generator — cover, spacing, duct bank width/height, and depth-to-centerline are dimensioned automatically, with manual dimension tool, drag-to-reposition, and typical/NTS callouts for cleaning up a submittal-ready, CAD-style section.

• Mixed voltage classes and circuit counts in one model — different circuits, different voltages, and different cable constructions can share the same duct bank.

• Imperial or metric units, project auto-save in-browser, undo history, and export of every per-cable and per-circuit result for your own records or downstream tools.

Who it's for

A power cable engineering tool for consultants, freelance electrical engineers, and small firms who need defensible, transparent duct bank ampacity calculations without paying for seat-based commercial software or reverse-engineering a spreadsheet. Every intermediate result — T1 through T4, screen loss factors, individual conductor temperatures — is exposed, so you can show your work.

Looking for a CYMCAP or ETAP alternative?

Commercial packages like CYMCAP and ETAP's cable ampacity modules are built for utilities and large firms running seat licenses. This tool covers the same core underground duct bank ampacity workflow — IEC 60287 and Neher-McGrath methods, duct bank thermal modeling, screen circulating currents, short-circuit withstand — as a single one-time purchase, with no per-seat licensing or annual maintenance fees. It's aimed at engineers who need one project's worth of rigor without one project's worth of software cost.

What you get

• A single .html file containing the full application — no installation, no account, no internet dependency once downloaded.

• Runs in any modern browser, on any machine, indefinitely.

• Your project data stays local to your browser. Save as to develop multiple scenarios

Requirements

Any modern desktop browser (Chrome, Edge, Firefox, Safari). No server, no plugins, no ongoing fees.

Engineering reference: IEC 60287-1-1 / IEC 60287-2-1 thermal and ampacity methods; Neher-McGrath with load-factor correction; IEC 60949 adiabatic short-circuit withstand.

Disclaimer

This tool is provided for reference and preliminary design purposes only. It is not a substitute for professional engineering judgment.

This calculator was developed independently and has not been certified, audited, or warranted by any professional engineering body. All outputs — including ampacity, thermal, electrical, and short-circuit results — must be independently reviewed and verified by a licensed Professional Engineer before being relied upon for any design, construction, permitting, or safety decision.

This software is sold "as is," without warranty of any kind, express or implied, including but not limited to warranties of accuracy, merchantability, or fitness for a particular purpose. The seller makes no representation that results produced by this tool comply with any applicable code, standard, or jurisdictional requirement. Use of this tool, and any decisions made based on its output, are at the sole risk of the user. The seller assumes no liability for any direct, indirect, incidental, or consequential damages, injury, loss, or cost arising from the use or misuse of this software or its results.

By purchasing and using this tool, you acknowledge and agree to the above.

One-time purchase. Single HTML file. Yours to keep.