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    Cable Ladder vs Perforated Cable Tray - Selection Guide (UK, 2025)

    Scope & references

    • BS 7671:2018+A2:2022 and A3:2024 (selection & erection; installation reference methods; grouping).

    • IET On‑Site Guide to BS 7671:2018+A2:2022 (practical application incl. escape‑route notes).

    The 7 drivers that do decide tray vs ladder

    Apply these in order. When a “YES” is met, you’ve chosen. If none apply, default to tray for mixed/small services and to ladder for heavy, predominantly SWA routes.

    1) Cable rigidity vs support geometry

    Question: Will the route carry mainly rigid, multicore SWA (or similar) that will span rung gaps neatly without sag at the manufacturer’s permissible cleat spacing?

    • YES → LADDER. Rung geometry aligns with armoured cable rigidity and routine cleating across rungs.

    • NO → TRAY. Continuous base prevents belly/sag on smaller or flexible cables and mixed services.
      (BS 7671 recognises both as free‑air methods; this is purely mechanical/support geometry.)

    2) Total installed mass per metre vs support span

    Question: After summing cable mass/m (all circuits) and applying your safety factor, does the route require longer support spans (fewer hangers/frames) than a perforated tray of similar width/load class can practically achieve?

    • YES → LADDER. Ladder systems generally offer higher load capacity at longer spans within BS EN 61537 load classes; confirm with manufacturer data.

    • NO → TRAY. If tray class at your planned span is adequate, there is no performance advantage in moving to ladder.
      (Product selection per BS EN 61537 load/deflection class; BS 7671 requires using compliant products.)

    3) Frequency and nature of drop‑outs

    Question: Do you need frequent mid‑span drops (many branch cables peeling off along the run) with minimal fabrication?

    • YES → LADDER. Open rungs allow simple drop‑throughs and tying/cleating.

    • NO → TRAY. Occasional exits are easier via accessories or simple side cut‑outs on tray.

    4) Cable mix and small services

    Question: Is the route carrying numerous small, flexible cables (e.g., controls, FP cables, data alongside power in segregated lanes/partitions) where continuous base simplifies dressing, segregation and fixing?

    • YES → TRAY. Continuous base helps containment and housekeeping.

    • NO → LADDER.

    5) Route complexity and accessories

    Question: Are there many tees, offsets, angle changes and tight routing constraints, where a richer standard accessory set reduces fabrication?

    • YES → TRAY. Tray systems typically provide more off‑the‑shelf fittings.

    • NO → LADDER (straight, long, open routes).

    6) Environment & drainage/cleanliness

    Question: Is the route exposed/outdoors, prone to water, dust or debris, where self‑draining, open containment minimises accumulation?

    • YES → LADDER. Open profiles shed water/debris readily.

    • NO → TRAY (especially indoors/ceilings where dust control and neatness are valued).

    7) Access and installation method

    Question: Would lighter sections with more frequent supports (but easier manual handling in congested ceilings) be advantageous?

    • YES → TRAY. Lighter channels, more hangers.

    • NO → LADDER. Heavier sections, fewer hangers (check fixings/structure).

    Worked example (what not to use as a lever)

    Case: 3‑core 25 mm² 70 °C PVC/SWA/PVC (Cu), multicore, on a straight riser/gantry; consider perforated tray (Method 31) vs ladder (Methods 32–34).

    • CCC: Appendix 4 classifies both as free‑air → same tabulated CCC for the same cable/formation (typical designers read ~110 A for this case from the correct table entry). There is no inherent CCC advantage to ladder.

    • Grouping: If you add parallel circuits, apply the same free‑air grouping tables; the factor doesn’t change just because you picked ladder instead of tray.

    Therefore, choose on mechanics:

    • If the run is long, with frequent drop‑outs and the tray class at your span is marginal → LADDER.

    • If the run is short/moderate, with small ancillary services added later, and accessory richness matters → TRAY.

    Containment selection
    Cable ladder and perforated cable tray shall be BS EN 61537 compliant and installed per BS 7671. Perforated tray (Installation Method 31) and ladder (Methods 32–34) shall be treated as free‑air reference methods (E/F) for current‑carrying capacity and Appendix 4 grouping (select the cable’s correct table and apply de‑rating as normal). Selection between tray and ladder shall be based on (i) cable rigidity vs support geometry; (ii) total installed mass per metre vs support span (within manufacturer load/deflection class); (iii) frequency of drop‑outs; (iv) cable mix/need for continuous base; (v) route accessory complexity; (vi) environmental drainage/cleanliness; (vii) access and manual‑handling considerations.
    Note: Compliance duties common to both (e.g., metallic fixings/support to prevent premature collapse in fire; escape‑route measures) remain BS 7671 obligations and do not drive tray vs ladder selection.

    Submittals/checklist (what you need from the supplier)

    • BS EN 61537 declaration of conformity and load/deflection class at the proposed span (include allowable deflection criterion).

    • Material & finish (e.g., pre‑galv vs hot‑dip, stainless grade) suitable for the external influences (environmental assessment per BS 7671).

    • Rung spacing / base perforation pattern and recommended cleat/tie spacing for your cable diameters.

    • Accessories list for all tees/offsets, and fixings/hanger schedules at the specified spans.

    • Method statements for penetrations/firestopping (selection‑neutral; still required).

    Cable Containment Selection – Checklist (Tray vs Ladder)

    #DriverAnswer these questions (tick)Default choice if YesSpec rules / evidence to record
    1Cable construction & stiffnessAre the circuits predominantly armoured (SWA/LSHF‑SWA), medium/large CSA, and stiff?LadderUse rung cleats matched to cable Ø and rung pitch. State SWA only on ladder in this route unless a detail drawing shows otherwise. Record installation method as E (ladder ≈ Method 34); CCC equivalence with Method 31 (perforated tray) must be assumed unless manufacturer data dictates otherwise—select on mechanical grounds, not CCC. (Install method refs: IET On‑Site Guide.)
    2Total mass & span (structural)Is the route long‑span (e.g., over doorways/plant) or carrying high cable mass (multiple SWA bundles)?LadderSize rungs/side‑rails to manufacturer load tables with stated support spacing. Record allowable uniformly distributed load (UDL) and support span per section; prohibit field changes without re‑check. (External influences and mechanical selection per BS 7671 Parts 52 & Appx. 5.)
    3Space & geometryIs there limited headroom/profile or frequent tight offsets/side exits to equipment?TrayUse perforated tray where a lower profile or dense accessory mounting (adapters, side‑exit, tie‑downs) is needed. Maintain min. bend radii per cable manufacturer. Record fitting types (formed bends vs. site‑set) and fixings per Regs. (Selection & erection: BS 7671 Ch. 52.)
    4Drop‑out frequency / changeabilityDo you need frequent drop‑outs along the run and expect future adds/moves?LadderLadder gives simple drop‑outs between rungs and robust cleating for laterals; define cleat spacing and gland support details. Prohibit drilling side‑rails; use approved accessories only. (Maintainability & workmanship: BS 7671 Ch. 34/52.)
    5Environment & corrosion classIs the route outdoors, in humid/wash‑down/industrial areas, or near aggressive atmospheres?Ladder (often)Select material/finish to external influence codes (e.g., AE, BE, etc. per Appendix 5). Specify finish (e.g., HDG/SS) and hardware in the same grade; mandate end‑cut treatment. Tray is acceptable in benign internal zones; state finish class in schedule. (BS 7671 Appendix 5 – External influences.)
    6Fire / life‑safety integrationDoes the route pass escape routes or need fire‑stopping at penetrations?Either (equal)Both must use non‑combustible supports and be fixed to resist premature collapse (BS 7671 Reg 521.10.202). Detail support spacing, ceiling/soffit fixings, and penetrations with tested seals; no plastic‑only fixings. Tag escape routes and provide access for inspection.
    7Programme, cost & buildabilityWill site logistics (weight/lengths), support frequency, and labour drive the choice?Tray for lightweight/many small circuits; Ladder for heavy SWA corridorsDocument rationale: tray = lighter sections but more supports; ladder = heavier sections but fewer supports. Select the most economical option that still satisfies Drivers 1–6. Record in design risk register. (General principles & maintainability: BS 7671 Parts 1/3/5.)

    Bottom line

    1. Containment type

      • Use cable ladder for primary power runs with predominantly SWA/LSHF‑SWA circuits and/or high load per metre, or where long spans are required.

      • Use perforated cable tray for mixed/smaller flexible circuits, dense side‑exits, and low‑profile routes.

      • Do not claim any inherent EMC advantage of ladder vs tray. EMC performance is provided by cable construction (e.g., SWA) and segregation per BS 7671 Section 528; apply separation distances and barriers as required by the installation design.

    2. Regulatory controls – apply to both ladder and tray

      • Supports & fixings: Provide metallic / non‑combustible fixings and supports throughout; design to prevent premature collapse in fire per BS 7671 Reg 521.10.202. Define max support spacing and allowable load per span; prohibit plastic‑only fixings anywhere on the route.

      • External influences: Select materials/finishes to the route’s external influence codes (BS 7671 Appendix 5). Complete the schedule to compare state indoor (electro-galv/PPG) vs. outdoor/industrial (HDG/SS) systems and compatible fasteners.

      • Segregation: Maintain functional segregation from other services and between LV/ELV per Section 528; use separators/stand‑off brackets where distances cannot be met. (Equal requirement for tray and ladder.)

      • Escape routes & fire‑stopping: Identify crossings of protected escape routes; coordinate supports, anchors and tested penetration seals. Provide access for inspection and labelling to suit periodic inspection per Part 6.

    3. Installation method / current‑carrying capacity (CCC)

      • Record the adopted installation method for thermal rating: perforated tray ≈ Method 31 (open, on tray); ladder ≈ Method 34 (open, on ladder). Treat CCC as equivalent for the same cable type/size unless manufacturer data indicates otherwise; cable selection is therefore mechanical/route‑led, not CCC‑led, for SWA on open metallic containment. (Method references: IET On‑Site Guide.)

    4. Mechanical execution

      • Use manufacturer load/span tables for section selection and hanger/anchor design; record UDL and point‑load allowances.

      • No field‑drilling of ladder side‑rails; use proprietary fittings. On tray, prefer formed fittings for primary bends; maintain minimum bend radii per the cable manufacturer. (Selection & erection: BS 7671 Ch. 52.)

    5. Change control / future capacity

      • For routes designated “future growth,” prefer ladder; define spare rung capacity and drop‑out positions. For dense LV controls/ICT in benign internal zones, prefer tray with defined accessory and tie points.

    Designer’s quick use decision flow

    1. Mostly SWA and/or heavy route? → Ladder

    2. Short spans, lots of side‑exits or low profile? → Tray

    3. Outdoors/industrial/corrosive? → Ladder (or Tray with upgraded finish) per Appx. 5 external influences.

    4. Escape routes present? → Either, but Reg 521.10.202 metal fixings & fire‑stopping mandatory.

    5. Programme/handling dominant? → Pick the most buildable option that still satisfies 1–4 and record rationale.

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