Cable Trays and Cable Ladders: Roll-Formed Profiles and Standards
There is a myth in the cable management trade that all cable trays are the same, so you just pick the cheapest one in the width you need. I have lost count of the projects where that assumption failed on the first load test. The truth is that trays differ in shape, material, perforation and the standard they are built to, and those differences decide whether the run sags, rusts or passes inspection.
Tray, ladder or wire mesh
Three families dominate. A perforated or ventilated tray is a continuous base with holes or slots for ventilation and cable ties. A ladder tray has two side rails with open rungs between them, which makes it strong for heavy power cables and easy to inspect. A wire mesh basket is welded steel wire, light and bendable by hand for data cabling. Solid bottom trays exist too, for drops and dirty environments. Each shape rolls from coil on a different line, and the punching pattern is what separates a tray line from a ladder line.
Materials
Most trays are galvanized steel, either pre-galvanized or hot dip galvanized to ISO 1461. Stainless 304 or 316 goes into chemical and coastal plants. Aluminium is chosen where weight matters, such as on ships or long roof runs, but it needs careful bonding at joints to avoid galvanic corrosion. The coating thickness decides the service life, so match it to the environment rather than the price list.
Perforations and profiles
The perforations are not decoration. Hole size, pitch and slot shape set how many cable ties you can fix and how the tray handles its own weight. Ventilated trays keep cables cooler; solid trays protect from falling objects and UV. Profile depth runs from shallow 35 mm to deep 100 mm or more for heavy load. The roll forming line must hold the width and return the edges cleanly or the fittings will not seat.
The standard that matters: IEC 61537
For tray and ladder systems the reference is IEC 61537. The current edition is IEC 61537:2023, the third edition, which replaced the 2006 version. It sets requirements and tests for safe working load, deflection, corrosion class, impact and electrical continuity, including how a tray may be used as a protective earth conductor. In the US market NEMA VE 1 covers ladders and NEMA VE 2 covers installation. A supplier who cannot quote the load class against IEC 61537 is guessing.
| Type | Best for | Typical load class |
|---|---|---|
| Ventilated tray | power and control, indoor | medium |
| Ladder tray | heavy power runs | high, Class 8C common |
| Wire mesh | data, light cabling | low |
| Solid bottom | drops, outdoor cover | medium |
What the roll forming line includes
A cable tray roll forming line is more than a roll former. It starts with a decoiler and a leveler to flatten the strip, then a servo punching press that cuts the holes and slots before forming. The roll former shapes the edges and depth, and a flying cut-off slices each length to size while the line runs. For ladders the line forms the side rails and a separate press or welder adds the rungs. Width change means changing the tooling set, not the whole machine.
Load and span
Load is quoted as safe working load at a stated support span. A hot dip galvanized steel ladder might carry about 200 kg per metre at a 1.0 m span, dropping to around 100 kg per metre at 2.0 m. Deflection is capped, often at L/200 of the span. Exceed the tested span and the run sags into the cables, which is exactly the failure the standard exists to prevent.
Takeaway
Hole patterns and accessories
The punching press sets the hole pattern, and that pattern must match the fixings the installer uses. Common trays use round holes of 6 to 9 mm on a pitch of 20 to 25 mm, with slot options for adjustment. Bends, tees and crosses are formed or pressed from the same section so the run turns corners without a different system. A tray line that only makes straight lengths forces the customer to buy fittings elsewhere, which breaks the coating and the load path at every joint. IEC 61537 expects the accessories to be made from the same material and tested to the same standard as the tray itself.
Deflection and support
IEC 61537 caps deflection, often at L/200 of the support span, and the safe working load is always stated with that span. A 600 mm wide ladder at a 2.0 m span may sit near 10 mm of sag at full load. The installer sets support spacing from the declared load, not from habit. A supplier who quotes a load without a span is not giving you a number you can build with, because the same tray carries far less at a longer gap.
Corrosion testing
Metallic trays for outdoor use are often salt spray tested to ISO 9227, with the better hot dip coatings expected past 500 hours before red rust. The corrosion class in IEC 61537:2023 is now more granular, so match the class to the site: a C5 coastal plant needs more than a dry indoor switch room. The coating and the standard together, not the catalogue photo, decide the ten-year result in the field.
Tray versus conduit
A tray is a support, not an enclosure. IEC 61537 is clear that trays and ladders hold and route cables but do not give full mechanical protection the way conduit or trunking does. That distinction matters when a spec calls for both: the tray carries the load, the conduit shields the sensitive run. Mixing them up leads to overspec or underspec, and both cost money on a long cable route.
Reading a supplier's claim
When a tray maker says "IEC 61537 compliant", ask for the test report and the declared safe working load with its span. Compliance without the number is a slogan. The report also shows the deflection and the corrosion class, which is the part your engineer actually needs to sign off the run before the first metre is hung.
Specify the tray by shape, material, the perforation you need and the load class from IEC 61537, not by price per metre. At ZTRFM we build tray and ladder roll forming lines to the width, hole pattern and coating our customers actually ship, because a tray that fails its load test fails the whole job.
