Cable Tray and Conduit Coordination in Ceilings

What You Need to Know

Cable trays and conduits share the ceiling void with ducts, pipes, and sprinklers. If you do not plan the layout early, services will clash, and someone has to move. That costs time and money. AS/NZS 3000 and AS 3013 set the rules for how far cables must sit from other services, how often you support the tray, and which cables can share a tray. This memo covers the numbers you need to get it right the first time.

• Keep cable trays at least 25 mm from any above-ground water or gas pipe (AS/NZS 3000, Cl 3.9.8.4)
• Keep power cables at least 50 mm from telecommunications cables. If you cannot get 50 mm, install a physical barrier between them (AS/NZS 3000, Cl 3.9.8.4)
• Keep cable trays at least 300 mm from hot pipework such as steam or hot water lines (AS/NZS 3000)
• Do not put water pipes, gas pipes, drainage, or any non-electrical service inside a cable tray (AS/NZS 3000, Cl 3.9.8)
• Use separate trays for power, control, and data cables. Mount power trays on top, then control, then data at the bottom (AS/NZS 3000, Cl 3.9.7)
• High voltage cables must never share a tray or enclosure with low voltage or extra-low voltage cables (AS/NZS 3000, Cl 3.9.7)
• Support horizontal cable trays every 1.5 to 3 metres, depending on the load. Use closer spacing for heavier cable loads (AS 3013 / manufacturer data)
• Support vertical cable tray runs every 2 metres or less (AS 3013)
• Cable fill must not exceed 50% of the tray cross-section for power cables. Allow 20 to 25% spare capacity for future cables (AS/NZS 3000)
• Fire-rate all cable penetrations through walls, floors, and ceilings to a minimum 2-hour rating (NCC 2025, Spec C3.15)

Picture a typical commercial office ceiling void. The structural slab sits at the top. Below it, you need to fit sprinkler pipes, HVAC ducts, cable trays, conduits, lighting, and a suspended ceiling grid. The total depth is often only 400 to 600 mm.

Start with the biggest services first. HVAC ducts take the most space and sit closest to the slab. Sprinkler mains run below the ducts. Cable trays slot underneath, above the ceiling grid. This top-down order gives you the best chance of fitting everything in.

For a typical floor with three 300 mm wide cable trays (power, control, and data), you need at least 150 mm vertical clearance between each stacked tray. That is 450 mm of vertical space just for the clearances. Add the tray depth itself (50 to 100 mm each) and you are using 600 mm or more. In a tight ceiling void, you may need to run trays side by side instead of stacked.

When trays run parallel at the same height, keep them at least 600 mm apart. This gap lets an electrician reach in and pull cables. Without it, maintenance becomes slow and expensive.

At every fire-rated wall or floor, seal the cable penetration with a tested and listed fire collar or intumescent wrap. This is not optional. If you miss one, the fire compartment fails, and the building will not get its occupation certificate.