Cable Tray Fill Calculator Formula
Understand the math behind the cable tray fill calculator. Each variable explained with a worked example.
Formulas Used
Tray Fill
fill_pct = tray_area > 0 ? total_cable_area / tray_area * 100 : 0Tray Cross-Section
tray_area_out = tray_areaMax Cables at 40% Fill
max_cables = single_cable_area > 0 ? floor(tray_area * 0.40 / single_cable_area) : 0Variables
| Variable | Description | Default |
|---|---|---|
tray_width | Tray Width(in) | 12 |
tray_depth | Usable Depth(in) | 4 |
num_cables | Number of Cables | 20 |
cable_od | Cable Outside Diameter(in) | 0.75 |
tray_area | Derived value= tray_width * tray_depth | calculated |
single_cable_area | Derived value= pi * pow(cable_od / 2, 2) | calculated |
total_cable_area | Derived value= num_cables * single_cable_area | calculated |
How It Works
Cable Tray Fill
Fill % = (Number of Cables x Cable Area) / Tray Area x 100
NEC Article 392 limits fill for cable trays. For multiconductor cables in a solid-bottom tray, total cable area must not exceed the tray cross-section area (the depth restriction acts as the limit). A practical target of 40% fill allows room for future additions and airflow.
Worked Example
20 cables (0.75 in OD) in a 12 x 4 inch tray.
tray_width = 12tray_depth = 4num_cables = 20cable_od = 0.75
- 01Tray area = 12 x 4 = 48 sq in
- 02Cable area each = pi x 0.375 squared = 0.442 sq in
- 03Total cable area = 20 x 0.442 = 8.84 sq in
- 04Fill = 8.84 / 48 x 100 = 18.4%
- 05Well within limits.
Ready to run the numbers?
Open Cable Tray Fill Calculator