Duct Bank Calculator

Bank width = 2 × side cover + columns × conduit OD + (columns − 1) × horizontal spacing
Bank height = top cover + bottom cover + rows × conduit OD + (rows − 1) × vertical spacing
Conduit fill (%) = total cable area ÷ conduit internal area × 100
Corrected ampacity = base ampacity × thermal factor × position factor × parallel sets
Voltage drop = phase factor × current × (R cosφ + X sinφ) × route length
Straight pull = reel back tension + cable weight × route length × friction
Bend pull = straight pull × e^(friction × total bend angle in radians)
Sidewall pressure = pulling tension ÷ bend radius
Concrete volume = gross bank volume − conduit displacement, plus waste
Project cost = materials + labor + equipment + overhead + contingency + tax

The thermal factor is an estimating model. Detailed cable ratings may require validated software, field thermal data, and project-specific standards.

1. Select the preferred unit system and design basis.
2. Enter the duct arrangement, conduit dimensions, spacing, cover, and route length.
3. Add every circuit and assign each circuit to a duct position.
4. Enter cable size, ampacity, electrical data, and loading information.
5. Provide soil, backfill, temperature, and thermal influence values.
6. Enter bend geometry, friction, cable weight, and pulling limits.
7. Add civil, reinforcement, and unit-cost information.
8. Submit the form and review every warning before using results.
9. Export schedules, quantities, diagrams, or the full report.

Planning the conduit arrangement

A duct bank groups underground conduits into an organized route. The arrangement affects space, concrete, cable pulling, and future expansion. Assign critical circuits before filling remaining positions.

Center ducts can experience stronger mutual heating. Edge ducts often receive better heat dissipation. Balanced circuit placement can improve usable cable capacity.

Checking conduit fill

Conduit fill compares cable area with conduit internal area. Cable shape, pulling configuration, and actual manufacturer dimensions still matter. Large cables may create jamming even below a selected fill limit.

Use actual cable outside diameters whenever available. Review bends and pulling clearances separately. Empty ducts should include pull ropes and suitable sealing provisions.

Understanding thermal loading

Underground cable temperature depends on current, losses, soil, backfill, depth, and nearby circuits. Dry soil can create poor heat transfer. High load factors increase sustained heating.

This calculator applies a planning derating factor. It does not replace a detailed finite-element or standards-based cable rating study. Confirm final ampacity with approved engineering methods.

Planning cable pulls

Long pulls and bends raise cable tension. Bend radius also controls sidewall pressure. Intermediate pull points may reduce both values.

Use manufacturer pulling limits for the selected conductor and pulling eye. Confirm lubricant assumptions and conduit condition. Recheck every route change before installation.

Estimating civil quantities

Concrete volume excludes conduit displacement and includes waste. Excavation includes trench width, bedding, and depth. Actual shoring, dewatering, restoration, and traffic control can increase costs.

Material prices vary by region and project scale. Use supplier quotations for final budgeting. Keep contingency for utility conflicts and field changes.