Cable tray at ladder fill

How this is calculated#

A cable tray or ladder holds cables side by side. AS/NZS 3008.1 rates cables on trays and ladders with grouping factors that hold for one layer of cables on each tier. So the question for a tray is how wide the cables are, laid in one layer, and how many tiers that takes. This tool lays them out and reads the factor.

You pick the cable family and list the sizes and counts. The overall diameters are the cable maker's figures that the conduit fill tool also uses. A multicore cable takes one diameter of width. A single‑core three‑phase circuit takes two diameters in trefoil and three laid flat. Touching cables sit side by side. Spaced cables have one diameter between them, as Tables 23 and 24 draw, and where sizes differ the tool uses the largest.

The standard sets no fill percentage for a tray, so the width kept free for later cables is yours to choose. The tool places each cable or circuit, in the order you list them, on the first tier with room. A run that does not fit one tier takes another, and stacked tiers are at least 300 mm apart for the factors to hold.

It then reads the grouping factor for the support, the spacing, the tiers used and the most cables or circuits on one tier. A count between two printed columns reads the next column up. Past the printed counts no factor is given. The mass per metre on each tier is the maker's catalogue figure.

Worked examples#

• A plant room tray: four 16 mm² and three 6 mm² multicore cables fit on 1 tier of a 300 mm perforated tray. They take 125.3 mm, a grouping factor of 0.73.
• Two 95 mm² trefoil submains on a 450 mm ladder fit on 1 tier, 60.8 mm wide, with a grouping factor of 0.95.
• Ten 35 mm² multicore feeders on a 300 mm tray need 2 tiers with a quarter of the width kept free. The fullest tier carries nine cables, a grouping factor of 0.68.
• Three flat 240 mm² circuits spaced on a 600 mm Australian ladder fit on 1 tier at a grouping factor of 1.

Limits#

The tool lays one cable family at a time: multicore three core and earth cables, or single‑core three‑phase circuits. It does not mix the two, model cables in more than one layer, or check segregation between services on the same tray. Use the segregation tool for that.

Single‑core widths use the diameter of unsheathed V‑90 single cores, the conduit fill figures. A sheathed or XLPE single core is wider, so allow for it. The mass is the cable alone. Check the tray or ladder against its maker's load and span tables, with the fixings and any future cables.

See also: Cable size, Correction factors and Conduit fill.