---
title: "Cable Tray Sizing Calculator: Ladder and Perforated Tray Sizing to AS/NZS 3000"
url: "https://scaleset.com.au/calculator/cable-tray"
description: "Free cable tray calculator for Australia: sizes ladder and perforated trays to AS/NZS 3000 with real Prysmian & Olex cable diameters and a free PDF report."
updated: "2026-10-13"
standards:
  - "AS/NZS 3000:2018: Electrical installations (Wiring Rules), wiring systems"
  - "AS/NZS 3008.1.1:2025: Electrical installations, selection of cables, Tables 3.34 and 3.35 (cable tray grouping, touching vs spaced)"
  - "AS/NZS 5000.1 (Electric cables) Polymeric insulated, voltages up to and including 0.6/1 kV"
  - "IEC 60364-5-52: Selection and erection of wiring systems (cable management)"
  - "The tray manufacturer’s published safe working load for the support span, the check the reported load in kg/m is for"
author: "Wisam Tozah (B.Eng (Electrical), MIEAust, CPEng, NER, NSW DBP, NSW PRE, APEC, IntPE(Aus))"
site: "ScaleSet"
license: "https://scaleset.com.au/terms"
usage: "Cite and link. Do not reproduce or train on this content."
---

# Cable Tray Sizing Calculator: Ladder and Perforated Tray Sizing to AS/NZS 3000

Source: https://scaleset.com.au/calculator/cable-tray

Free Australian cable tray sizing calculator. Pick from real Prysmian and Olex cable catalogue data, choose flat or trefoil arrangements, touching or spaced layouts, and get the narrowest standard tray, its side rail depth and the tier allocation, with a PDF report (downloading it needs a free account; your own logo and accent colour on it are Pro).

## Key facts

- Tray sizing is based on actual cable outer diameters against the tray's usable width, with the reserve capacity you set applied on top.
- Depth is sized separately from width: cables laid flat need their outer diameter, while a trefoil group stands 1.87 times the outer diameter high because the third cable sits in the hollow on top. The result gives the shallowest standard side rail (50, 75, 100 or 150 mm) that clears the tallest item.
- The calculator ships manufacturer catalogue data for 380+ Prysmian and Olex cables.
- Layering and spacing choices change the required tray size. Where one tray will not do, the bundle is stacked into tiers and the narrowest tray achieving the fewest tiers is recommended.
- Cable load is reported from published catalogue masses. Where a cable carries no mass figure it is left out and the load is marked as partial or unavailable rather than shown as zero.
- The arrangement you pick is also the cables’ grouping arrangement. AS/NZS 3008.1.1:2025 Table 3.34 (single-core circuits) and Table 3.35 (multicore) give the grouping factor for it and the number of circuits on the tier, and the tray result does not apply it: size the cables with that factor. Spacing costs tray width and lifts the factor; three multicore circuits touching on one unperforated tray take 0.78, spaced 0.94.

## Who this page is for

Electrical engineers, designers, contractors and project drafters sizing ladder and perforated cable trays for AS/NZS 3000:2018 installations, sub-mains and mains cable runs in industrial, commercial and infrastructure projects across Australia and New Zealand.

## Relevant standards

- AS/NZS 3000:2018: Electrical installations (Wiring Rules), wiring systems
- AS/NZS 3008.1.1:2025: Electrical installations, selection of cables, Tables 3.34 and 3.35 (cable tray grouping, touching vs spaced)
- AS/NZS 5000.1 (Electric cables) Polymeric insulated, voltages up to and including 0.6/1 kV
- IEC 60364-5-52: Selection and erection of wiring systems (cable management)
- The tray manufacturer’s published safe working load for the support span, the check the reported load in kg/m is for

## What this tool does

- Pick from 380+ Prysmian Australia and Olex (Nexans) cable products with manufacturer-published outer diameter and mass: no hand-typed approximations.
- Flat (touching), flat (spaced), trefoil (touching) and trefoil (spaced) layouts on a per-cable basis: mix arrangements within the same tray.
- Trefoil width = 2 × cable diameter geometry, with automatic grouping of three matching single-core cables per circuit.
- Reserve capacity allowance (default 20%) applied per-tier so each tier preserves spare room for future cables.
- Multi-tier allocation when the smallest tray cannot fit the bundle: packs cables into stacked tiers up to the user-defined maximum tray width.
- Cable mass in kg/m per tier so designers can cross-check against the tray manufacturer’s safe working load for the support span.
- Standard nominal widths: 50, 75, 100, 150, 225, 300, 450, 600, 750 and 900 mm, the common Australian tray product ladder.
- PDF report with the cable schedule, tier allocation and to-scale cross-section, with manufacturer catalogue references for procurement (downloading it needs a free account; your own logo and accent colour on it are Pro).

## How to size a cable tray for AS/NZS 3000:2018

1. **Pick the cable manufacturer** — Filter the catalogue to Prysmian Australia or Olex (Nexans). The mass per metre and outer diameter feed both the width calculation and the tray-load weight estimate.
2. **Choose a cable family** — Select the construction family for each cable on the tray. SWA armoured cables, SDI single-core and flex variants all have different outer diameters and masses; the calculator applies the right values automatically.
3. **Pick the layout method per cable** — Flat (touching) packs cables shoulder-to-shoulder, flat (spaced) adds a configurable diameter gap, trefoil (touching) groups three matching single-cores into an equilateral triangle of width 2D, and trefoil (spaced) adds a gap between trefoil groups.
4. **Set the spacing factor for spaced layouts** — For AS/NZS 3008.1.1:2025 spaced-arrangement derating relief (AS/NZS 3008.1.1 Tables 3.34 and 3.35), spacing must be at least one cable diameter. Set Spacing (D) to 1.0 for that one-diameter gap, or 2.0 to 3.0 if your specification requires more.
5. **Set reserve capacity and maximum tray width** — Reserve is the future-cable allowance (commonly 20 to 50%). The maximum tray width caps the largest single tier the calculator may select; beyond that limit the calculator stacks tiers.
6. **Review the recommendation and export the PDF** — The output shows recommended tray nominal width, tier count, mass per metre, used width and a cross-section sketch. Export the PDF for the design pack; cross-check the mass against the tray vendor span-load curve.

## Complete guide to cable tray sizing for AS/NZS 3000:2018 projects

### Geometry: why flat and trefoil arrangements have different tray widths

Three identical single-core cables of diameter D packed in a touching trefoil sit 2D wide, because the two bottom cables sit side by side and the third rests in the groove above them. The group stands about 1.87D tall. The calculator therefore consumes 2D of tray width per trefoil group, versus 3D of tray width if the same three cables were laid flat and touching. Trefoil reduces the tray width but needs a deeper side rail.

For spaced arrangements, AS/NZS 3008.1.1:2025 Tables 3.34 and 3.35 take a gap of one cable diameter between adjacent circuits, flat or trefoil. The gap pays for itself in rating: six multicore circuits in one tier take 0.91 spaced on a perforated tray against 0.76 touching, and 1.00 spaced on a ladder (AS/NZS 3008.1.1 Table 3.35).

### AS/NZS 3008.1.1 grouping derating and tray-layout decisions

Cables laid touching in a single layer on a tray are derated under AS/NZS 3008.1.1:2025 Table 3.35 (multicore) or Table 3.34 (single-core). On a perforated tray the derating factor drops from 1.00 for a single circuit to 0.82 for three circuits and 0.76 for six in the same touching layer; a ladder holds 0.79 at six, and an unperforated tray falls to 0.71.

Those same tables then offer relief when cables are spaced: by one cable diameter between adjacent circuits, whether laid flat or in trefoil (D in the tables is the cable diameter, not a trefoil width). The trade-off is direct: spaced layouts use more tray width but allow smaller cable sizes (less derating), and touching layouts use less tray width but force larger cables (more derating). The ScaleSet calculator handles the geometry side; the ScaleSet cable selection calculator handles the current-rating side.

### Reserve capacity: what value to pick

Industry practice for greenfield commercial fit-outs in Australia is 25 to 50% reserve capacity on cable trays, with 20% common for tight retrofit and infrastructure projects. Reserve allows for future cable adds without re-trunking the building. The ScaleSet calculator applies reserve as a per-tier multiplier on usable width, so each populated tier preserves the same reserve fraction.

Where a client specifies more, as data centre and hospital clients often do, set the reserve up to 100% and use the maximum tray width limit to cap the largest single tier; the calculator will stack tiers if the bundle exceeds that cap.

### Tray load: cable mass per metre and tray span

The calculator reads each cable’s mass from the Prysmian and Olex catalogues and reports the load in kg/m for each tier and in total; a cable with no published mass is left out and the load is marked partial. Compare each tier’s load with the tray manufacturer’s safe working load for the product and the support span.

AS/NZS 3000:2018 does not publish numeric tray load limits: those come from the tray manufacturer. The ScaleSet PDF includes total mass per metre and per-tier mass so the responsible engineer can perform the vendor check.

### Standard cable tray sizes in Australia

Cable tray products from Australian distributors typically follow the 50, 75, 100, 150, 225, 300, 450, 600, 750 and 900 mm nominal width ladder. The calculator selects the smallest tray whose actual width accommodates the raw cable bundle plus reserve. Trays wider than 900 mm are outside this calculator: it stacks tiers instead.

The calculator gives the depth as well as the width: the shallowest standard side rail of 50, 75, 100 or 150 mm that clears the tallest item on a tier, a flat cable at its own diameter and a trefoil group at 1.87 times it. Where even 150 mm is too shallow it says which cable stands too tall.

### When to use cable tray, conduit or ladder

Cable tray (perforated and ladder) is preferred for sub-mains, mains and submains feeders inside plant rooms, risers and ceiling spaces where pulling tolerance, future modification and ventilation matter more than mechanical protection. Conduit (HD-PVC, medium-duty) is preferred for final subcircuits and exposed runs where mechanical protection, water ingress and aesthetics dominate.

For mixed installations (tray on the riser, conduit on the floor) the ScaleSet conduit sizing calculator and cable tray sizing calculator share the same Prysmian and Olex catalogue so cable picks remain consistent across both reports.

## Key terms

- **Cable tray** — A support system carrying cables along a route, in ladder or perforated form. Sizing it means choosing a width and depth that hold the cables with the reserve capacity the design allows for.
- **Usable width** — The width a tier gives the cables once the reserve capacity is kept clear: the tray width divided by one plus the reserve, so 83% of it at the default 20%. Packing is calculated against this.
- **Trefoil** — Three single-core cables bundled in a triangle. A trefoil group stands about 1.87 times one cable diameter high, because the third cable sits in the hollow formed by the other two.
- **Flat (laid) formation** — Single-core cables laid side by side in one plane. It occupies more width than trefoil but only one cable diameter of height, and it derates differently.
- **Grouping factor** — The AS/NZS 3008.1.1 correction factor for cables that heat one another. On a tray it is read from AS/NZS 3008.1.1 Table 3.34 for circuits of single-core cables and Table 3.35 for multicore cables, by the arrangement (touching or spaced, flat or trefoil), the number of circuits per tier and the number of tiers. It reduces the cable’s current-carrying capacity, not the tray size.
- **Touching vs spaced** — Whether adjacent cables or groups are laid in contact or separated. Spacing costs tray width but improves heat dissipation, which is why it interacts with the AS/NZS 3008.1.1 grouping factor.
- **Reserve capacity** — Spare tray width deliberately left for future cables. It is a design allowance rather than a requirement of the standard, and it is applied on top of the calculated packing.
- **Tier** — One level of a multi-level tray stack. Allocating cables across tiers keeps each tray within its usable width; each tier’s load in kg/m is reported so it can be checked against the tray’s safe working load.

## Frequently asked questions

### How do I calculate cable tray width?

Add up the outer diameters of the cables laid side by side (2D for each touching trefoil group), add the gaps for any spaced cables, then add your reserve capacity and pick the narrowest standard width (50, 75, 100, 150, 225, 300, 450, 600, 750 or 900 mm) that holds the total. The ScaleSet cable tray calculator does this from Prysmian and Olex catalogue diameters, stacks the cables into tiers when no tray up to your maximum width holds them in one, and gives the side rail depth that clears the tallest cable or trefoil group.

### How do I calculate trefoil cable tray width?

A touching trefoil group of three identical single-core cables of diameter D takes 2D of tray width, because two cables sit side by side and the third rests in the groove above them, and it stands about 1.87D high, which sets the side rail depth. For spaced trefoil groups, add the spacing factor times D between groups. The ScaleSet cable tray calculator groups three of the same single-core cable into a trefoil automatically when a trefoil layout is selected; a leftover one or two are laid flat.

### Should cables on a tray be touching or spaced?

Touching cables use less tray width but take the bigger grouping derating in AS/NZS 3008.1.1:2025 Tables 3.34 (single-core circuits) and 3.35 (multicore). Six multicore circuits touching in one tier take 0.76 on a perforated tray and 0.71 on an unperforated one; spaced by one cable diameter on a perforated tray they take 0.91, so you get most of the rating back for the extra width. For sub-mains running near their rating, spacing is usually worth it. The tray calculator sizes the width for either layout; apply the factor in the Cable Selection calculator.

### How do I work out the cable load on a tray in kg per metre?

Add up the published mass per metre of every cable on the tray. The ScaleSet calculator does this from the Prysmian and Olex catalogue masses and reports the total and each tier’s load in kg/m; a cable with no published mass is left out and the load is marked partial rather than shown low. AS/NZS 3000:2018 sets no numeric load limit for cable tray, so compare each tier’s load with the tray manufacturer’s safe working load for your product and support span.

### What reserve capacity should I use for cable tray sizing in Australia?

AS/NZS 3000 sets no figure for it: reserve is a design allowance. Common practice is 25 to 50% for greenfield commercial fit-outs, about 20% for tight retrofits and infrastructure, and 50 to 100% where the client specifies it, as on data centres and hospitals. The ScaleSet calculator defaults to 20% and accepts 0% to 100%. The reserve sets how much of each tier the cables may fill (at 20%, up to 83% of the width), so it directly drives the recommended tray width.

### Can I mix flat and trefoil cables on the same tray?

Yes. Each cable row carries its own layout: three single-cores in trefoil for the heavy sub-main and flat-touching multicores for the lighting circuits can share one tier. Each item takes its own width (2D for a trefoil, D for a flat cable, plus the gap for a spaced one) and the calculator packs them largest first.

### What tray width do I need for four 25 mm² 4-core-and-earth XLPE cables?

A 150 mm tray. Four touching 25 mm² 4C+E XLPE copper multicores at 24.9 mm outer diameter need 99.6 mm of raw width, and the default 20% reserve takes that to 119.5 mm, so 150 mm is the narrowest tray that holds them in one tier, on a 50 mm side rail. A 100 mm tray would only do with the reserve under 1%. Steel-wire armoured versions are larger, so pick the exact cable from the catalogue and let the calculator confirm the width.

### Does the calculator work for ladder, perforated and solid-bottom trays?

Yes. The width and side rail depth it gives apply to ladder, perforated and solid-bottom (unperforated) tray alike, because the cables take the same room on each. The tray type changes the cables’ current rating instead: AS/NZS 3008.1.1:2025 Tables 3.34 and 3.35 have separate rows for each, so six multicore circuits touching in one tier take 0.79 on a ladder, 0.76 on a perforated tray and 0.71 on an unperforated one. Read the factor for your tray type when sizing the cables.

### Is this cable tray sizing calculator free?

Yes. The cable tray sizing calculator is free to use online, with no sign-up to calculate. Downloading the PDF report needs a free account, and saving the job to your device as a project file needs none. A custom logo and accent colour on the report, cloud save and project workspaces are Pro features.

### Is there a cable tray fill limit in AS/NZS 3000?

No. AS/NZS 3000:2018 sets no fill percentage for cable tray the way AS/NZS 3000 Appendix C sets a space factor for conduit. Tray fill is worked as width: the cables lie in a single layer on each tier at their catalogue diameters, with any spacing, and the reserve capacity you set is the spare width left over. With the default 20% reserve the cables may take up to 83% of each tier’s width. Grouping derating is separate, and it is often what limits how tightly you pack the tray.

## Related ScaleSet pages

- [Conduit Sizing Calculator](https://scaleset.com.au/calculator/conduit-sizing)
- [Cable Selection Calculator](https://scaleset.com.au/calculator/cable-selection)
- [Voltage Drop Calculator](https://scaleset.com.au/calculator/voltage-drop)
- [Derating Factor Calculator](https://scaleset.com.au/calculator/correction-factor)
- [Maximum Demand Calculator](https://scaleset.com.au/calculator/max-demand)
- [Earthing Cable Size Calculator](https://scaleset.com.au/calculator/earth-cable-size)
- [Design Guides](https://scaleset.com.au/design-guide)
- [Useful Links](https://scaleset.com.au/useful-links)

## About this page

Methods built and reviewed by Wisam Tozah (CPEng, NER, MIEAust), Sydney, Australia. How the methods are tested and reviewed: https://scaleset.com.au/verification. ScaleSet is a design aid: your inputs and results are not reviewed or certified, and responsibility for the design stays with the engineer who issues it. Profile: https://scaleset.com.au/creator.

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