Conveyor-cell panels typically run 24 VDC I/O, 480 V three-phase VFD feeders, encoder shielded pairs, and Cat6 fieldbus in the same cabinet, and the wiring duct is the mechanical envelope that decides whether that mix stays serviceable or turns into a service nightmare. The 2026 specification map comes down to four binding gates: material, fire envelope, slot/finger geometry, and thermal derating, with panel-thermal derating above 50 °C.
Across ABB's ty-duct and metric-wiring-duct ranges, TE's ENTRELEC 24/40/60/80/100/120 mm profiles, Panduit's Type F/D/G/FS/C/HS/H/HN/MC catalog, HellermannTyton's HelaDuct HTWD series and Salzer's PVC-FRLS ducts, every published offering hits the same dimensional envelope (widths 24–120 mm, metric slot pitches 10/12.5/20 mm), so the actual differentiation lives in the body compound and the fire-test certificate, not in the outside dimensions [S1][S5][S6][S7].
Material family: standard PVC vs halogen-free vs PVC-FRLS
Standard rigid PVC is the default and is suitable for general-purpose conveyor cells, but the 2026 buy-spec has shifted to halogen-free grades for any cell shipping into rail, marine, public-building or tunnel-fed packaging lines; ABB's halogen-free line and TE's low-smoke halogen-free range target those duty cycles [S1][S6]. Salzer publishes a PVC-FRLS (fire-retardant low-smoke) variant tested to ASTM D 2863 with a minimum Limiting Oxygen Index of 29 (typical ≥ 40) and a temperature index above 200 °C, which is the same LOI gate most European panel shops have been writing into conveyor-cell MRs since 2024 [S4].
Choose PVC when ambient stays below 50 °C and the cabinet is not on a fire-listed egress line; choose halogen-free when the cell sits inside a warehouse with sprinkler-fed egress, when shipping into IEC 60332-1 / EN 45545-2 jurisdictions, or when the spec sheet calls for low smoke density (Salzer's SDR is rated below 45 % under ASTM D 2843, against a 60 % ceiling) [S4].
Fire envelope: UL94 V-0, LOI, temperature index, smoke density
For a U.S. conveyor-cell build, the binding fire numbers are UL94 V-0 flammability rating (self-extinguishing within 10 s on both vertical and horizontal specimens) on the body compound, plus a continuous-use temperature index above 90 °C; for an EU build, the binding numbers are LOI ≥ 29 and smoke density below 60 % per ASTM D 2843, both of which Salzer's PVC-FRLS line meets with margins [S4]. The temperature-index test (also ASTM D 2863) reports above 200 °C for Salzer's compound, meaning the duct will not propagate flame in normal-air (21 % O2) conditions until the surface is well above any UL508A panel interior ever reaches.
Do not run standard PVC in cells where the drive cabinet is mounted directly above a motor with class F (155 °C) insulation, where the VFD is bolted to the same panel back-plate, or where the cell is in a Class II dust location; halogen-free grades are the correct answer in all three cases, and the spec should be written with a quantitative floor (LOI ≥ 29, SDR < 60, UL94 V-0), not a vague 'flame-retardant' phrase [S1][S4][S6].
Slot/finger geometry and wire-gauge matching
Slot pitch and finger width decide whether the duct is a serviceable harness or a wire salad: Panduit publishes Type F (narrow slots, narrow fingers) for terminations of #22–#16 AWG control wiring, Type G (wide slots, wide fingers) for #14–#10 AWG power, Type D (round holes) for breakout nodes, and Type HS / HN / HC hinged-cover variants when the cabinet door swings into the duct run [S5]. TE's ENTRELEC profiles in 24/40/60/80/100/120 mm widths map directly onto these duties, with the 24 mm and 40 mm sizes carrying encoder shielded pairs and sensor leads, 60–80 mm carrying the 24 VDC I/O bundles, and 100–120 mm carrying the VFD output conductors [S6].
HellermannTyton's HelaDuct HTWD-BWR base wire retainers plus the HTWD-NFWR / HTWD-WFWR retainer family are the accessories that keep the bundle inside the duct during VFD cabinet punch-press, and omitting them is the single most common reason a 600 V conductor ends up resting on a duct edge that was never rated for the fault-current let-through [S7]. For conveyor cells where the panel is mounted on the conveyor itself (vibration present), specify the base retainer plus a hinged cover, not a snap-on cover; the snap-on covers walk off under continuous 0.5 g vibration.
Thermal derating and fill ratio inside an enclosed panel
Standard PVC starts to soften above 60 °C continuous and is normally derated from 50 °C ambient; halogen-free grades push that ceiling to 90–100 °C continuous, which is why every VFD cabinet with a 480 V, 50 A drive bolted to the back-plate should be specced halogen-free even if the room ambient is benign [S1][S6]. Fill ratio should not exceed 60 % of the duct's internal cross-section, per the de-facto industry convention (Panduit's catalog diagrams and TE's ENTRELEC installation sheets both mark the 60 % line on their cross-section drawings) [S5][S6].
At higher fill ratios the heat-rise inside the duct goes non-linear, the bundle's current-carrying capacity drops, and the plasticizer in standard PVC migrates into the jacket of any PVC-jacketed cable that shares the run — that migration is the root cause of the 'stuck-together wires' failure mode most field engineers see on five-year-old conveyor panels. The 60 % fill rule plus a halogen-free body for any run that touches a VFD output kills that failure mode.
Selection criteria table for conveyor-cell duty
For a 480 V VFD-fed conveyor cell with mixed 24 VDC I/O and Cat6 fieldbus, the comparative pick is: (a) standard PVC Type G 60×60 mm with snap cover for the 24 VDC bundle — cheapest, fine if ambient stays below 50 °C and no fire-listed egress; (b) halogen-free Type F 40×40 mm with hinged cover and HTWD-BWR retainers for the encoder / shielded pair run — required where the spec calls for low-smoke or where the cell ships into EN 45545-2 territory; (c) PVC-FRLS 100×80 mm with hinged cover for the VFD output conductors — needed for the LOI ≥ 29 / SDR < 60 fire envelope and the higher continuous-temperature margin [S4][S5][S6][S7].
Do not pick standard PVC for the VFD output run; do not pick halogen-free for the entire panel just because marketing pushed it — the halogen-free premium is real and should be spent only where the fire or temperature envelope demands it. The same logic applies to busway trunking choices elsewhere in the same cell, where ampacity and fault-withstand dominate over fire envelope.
Who should NOT pick the mainstream option and why
Standard rigid PVC should not be specified in cells with any of the following duty markers: VFD output conductors running through the duct, ambient above 50 °C, exposed to hydraulic fluid or cutting-oil mist, or installed in a food-grade conveyor cell where the washdown protocol uses alkaline cleaners. In all four cases halogen-free or PVC-FRLS is the correct answer, and the spec should pin the fire-test certificate, not a marketing phrase [S1][S4].
For a control-cable run sharing the same duct, the control cable selection guide addresses the conductor-side spec gates that the duct then has to mechanically accept; mismatched cable OD and duct slot width is the second most common conveyor-panel rework cause after wrong fill ratio. For the upstream 24 VDC signal-isolation hardware, signal isolator selection covers the I/O-side architecture decisions that decide how many conductors the duct actually has to carry.
Trackable signals and the next spec node
Until those land, the safe 2026 spec is halogen-free body plus quantitative fire envelope (LOI ≥ 29, SDR < 60, UL94 V-0) plus hinged cover plus base retainers, written as numeric floors in the MR, not as adjectives. [S4]
Spec-level background on the components involved: wiring duct, load cell, and spiral duct.