PVC Cable Trunking & Slotted Panel Duct Sizing: EN 50085 40–50% Fill Ratio Chart
Sizing EN 50085 surface PVC trunking, floor ducts, and slotted control-panel wiring ducts using the 40–50% usable cross-section rule, with CAT6 and 3×2.5 mm² capacity tables.
PVC cable trunking and slotted panel wiring duct sizing under EN 50085-1 / EN 50085-2-3 protects conductors mechanically while maintaining thermal airflow and room for future circuit additions. Never size a duct to 100% geometric area; engineering practice restricts usable cable fill to 40% – 50% of internal cross-sectional area.
> Related Category: Compare wall, floor, and cabinet duct profiles in Cable Trunking, Panel Wiring Ducts, and PVC Cable Trunking.
1. The EN 50085 40–50% usable fill ratio formula
Because circular jackets leave interstitial air voids when bundled, calculate total conductor area against a 45% net fill ceiling (`40%` for loaded power circuits to limit mutual heating, `50%` for low-voltage control/data):
- Internal duct area: `A_duct = Width (W) × Height (H)` (`mm²`)
- Allowable bundle area: `Σ (π × D² / 4) ≤ 0.45 × W × H`
2. Standard PVC trunking capacity chart (`CAT6` vs `3×2.5 mm²`)
Approximate maximum cable counts at 45% fill (`CAT6 ≈ Ø6 mm`, `3×2.5 mm² NYM/H05VV-F ≈ Ø10.5 mm`):
| Trunking size (W × H) | Gross area (`mm²`) | Max CAT6 (`Ø6 mm`) | Max `3×2.5 mm²` (`Ø10.5 mm`) | Typical installation |
|---|---|---|---|---|
| 16 × 16 mm | 256 mm² | 2 – 3 | 1 | Single switch/socket drop or 1 patch run |
| 25 × 16 mm | 400 mm² | 4 – 5 | 1 – 2 | Skirting twin socket or CCTV + data drop |
| 40 × 25 mm | 1,000 mm² | 12 – 14 | 4 | Office workstation perimeter distribution |
| 60 × 40 mm | 2,400 mm² | 30 – 34 | 9 – 10 | Corridor sub-main or multi-compartment dado |
| 100 × 100 mm | 10,000 mm² | 120+ | 40 | Server room riser and workshop main trunk |
3. Adhesive, floor-over, slotted panel, and galvanized trunking selection
- Self-adhesive vs screw-fixed trunking: Adhesive plastic cable trunking speeds up light single-cable drops on degreased tile or glass, but overhead runs and profiles `≥ 40×25 mm` must be anchored with wall plugs and washer-head screws every 40–50 cm so thermal creep never pops the backing tape.
- Curved floor trunking: Across doorways and open-plan walkways, use low-profile floor herringbone cable trunking with internal dividers separating mains and data cores.
- EN 50085-2-3 slotted panel wiring ducts: Panel wiring ducts (`25×40` to `80×100 mm`, `UL94 V-0` rigid PVC or halogen-free `PC/ABS`) route `0.5–10 mm²` ferrules directly to DIN-rail terminal blocks; choose narrow `4/6 mm` fingers for high-density PLC I/O and `8/12 mm` fingers for power contactors.
- Metallic trunking finishes: Specify pre-galvanized sheet steel indoors and hot-dip galvanized steel in damp parking decks, coastal sites, and outdoor pipe bridges.
Frequently asked questions
Can 230 V power cables and CAT6 data cables share one PVC trunking?
Not inside a single undivided chamber—parallel coupling degrades Ethernet SNR and violates segregation rules. Use multi-compartment trunking with a snap-in PVC divider wall (or shielded CAT6A FTP cable).
Why do trunking lids pop open at 90° wall corners?
Miter-cutting a sharp 90° bend forces stiff `2.5–6 mm²` or CAT6 cables below their `4 × D` minimum bend radius, pushing outward against the lid. Molded internal, external, and flat-angle fittings preserve bend radius and lock over the cover seam.
When should halogen-free slotted panel ducts be specified?
Specify halogen-free (`EN 50642` / `UL94 V-0` PC-ABS) slotted ducts in hospitals, rail rolling stock, data centers, and marine switchboards where PVC's corrosive HCl smoke is prohibited.
Does bundling multiple power circuits inside closed trunking reduce cable ampacity?
Yes. Under IEC 60364-5-52 (Installation Method B1/B2), grouping 2, 3, or 4 loaded circuits inside one closed trunking applies grouping derating factors (`0.80`, `0.70`, `0.65`) to each conductor's continuous current rating.