Most cable tray problems are written into the specification, not created on site. A tray that is too shallow for the cable bend radius, a load class quoted without the safety factor, a galvanised finish described only as “hot-dip” with no coating thickness — each of these passes through procurement unnoticed and surfaces later as rework, a failed inspection or a corrosion claim. The ten errors below account for most of the failures we see.
The standards a tray specification has to reference
IEC 61537 is the product standard for cable tray systems and cable ladder systems, covering dimensions, mechanical performance, and the load testing that establishes a declared safe working load. In North America, NEMA VE 1 defines metal cable tray performance including load classes and the safety factor applied to them, while installation is governed by NEC Article 392 — with 392.22 for fill and 392.80 for ampacity adjustment. In Europe, EN 61537 is the harmonised equivalent, and IEC 60364-5-52 governs cable selection and current-carrying capacity in the installation.
A specification that cites none of these, and instead describes the product as “galvanised steel cable tray, heavy duty”, gives the supplier nothing to comply with and the inspector nothing to check.
Ten specification errors, and what each one costs
1. Quoting a load class without the safety factor
NEMA VE 1 load classes describe a working load, and the tray is tested to a multiple of it — the safety factor is applied to the yield strength of the material, commonly 1.5 times the working load. A tray quoted as “Class C” tells you the working load, provided the manufacturer’s test report is for that class and that span. It does not tell you what happens at 3 m span with a point load at mid-span. Ask for the load-deflection curve at your actual support spacing.
2. Sizing on cable count instead of cable weight
Fill and load are different calculations. A tray can be 40% filled by area and still overloaded if the cables are heavy armoured power cables. Calculate mass per metre from the cable schedule, add the tray’s own weight, and add ice and wind where the run is external.
3. Applying area fill without the derating rules
NEC 392.22 limits the permitted fill by table, and 392.80 requires ampacity adjustment for conductors in tray depending on whether they are randomly installed or maintained in a single layer. IEC installations reach a similar outcome through IEC 60364-5-52 grouping factors. Specifying “40% fill” as a universal rule ignores both. The consequence is cables that were sized correctly in isolation and are now running above their installed rating.
4. Support spacing taken from a catalogue instead of the project
Support spacing depends on load, on tray type — wire mesh behaves differently from ladder — and on concentrated loads at bends and tees. Fittings need support within a defined distance; that distance comes from the manufacturer, not from a generic 1.5 m rule.
5. No expansion joint, or one in the wrong place
Steel tray expands roughly 12 × 10-6 per K. A 60 m external run with a 50 K temperature swing moves about 36 mm. Without expansion joints the movement goes into the supports and the fixings, and the tray buckles or the anchors pull. Place joints at structural movement joints and at intervals the manufacturer specifies, and never trap a joint between two rigidly fixed supports.
6. Earthing assumed from bolted joints
IEC 61537 and good practice require the tray system to be electrically continuous, but continuity through bolted splice plates is only reliable if the joint is designed for it — plain galvanised surfaces under a bolt are not a dependable earth path after a few years of corrosion. Use dedicated bonding jumpers or listed bonding splice plates, and confirm the earth fault loop impedance at the far end rather than at the first support.
7. Power and data sharing a tray with no divider
Mixing power and data in one tray without a metallic divider compromises both safety and signal integrity. A divider gives physical separation; the distance still has to come from the EMC guidance applicable to the project. A tray filled with both, in no defined order, is also impossible to maintain.
8. Finishing specified as “hot-dip galvanised” with no thickness
| Steel thickness | ISO 1461 minimum local coating | Environment it suits |
|---|---|---|
| Under 1.5 mm | 45 µm | Indoor, dry, low corrosivity |
| 1.5 to 3 mm | 55 µm | General indoor industrial |
| 3 to 6 mm | 70 µm | Outdoor sheltered, moderate humidity |
| Over 6 mm | 85 µm | Heavier sections, more aggressive exposure |
These are ISO 1461 minimum local values; average thickness is higher. For coastal or chemical exposure the specification should name a corrosivity category and the coating system, not just the process. A 45 µm coating and a 120 µm duplex system are both “hot-dip galvanised” and are not interchangeable.
9. Depth chosen without checking the bend radius
A tray must accept the cable’s minimum bending radius, expressed by IEC 60364-5-52 as a multiple of cable diameter — 12 to 15 times the diameter for many armoured power cables. A 100 mm deep tray cannot take a 35 mm cable bending out of its base. The same applies at drop-outs and at enclosure entries.
10. No fire-stop where the tray crosses a compartment line
Every wall and floor penetration is a compartment boundary. The seal must be tested for the tray type and the penetration size — a mortar infill around a ladder tray has no test evidence. The fire-stop also has to survive the tray’s thermal movement; a rigid plug in a moving run cracks.
Summary: error, consequence, correction
| Specification error | Typical consequence | Correct approach |
|---|---|---|
| Load class quoted without span | Tray deflects at mid-span, cables over-stressed | Load-deflection data at the project span |
| Fill by count, not weight | Overloaded supports, sagging run | Mass per metre from the cable schedule |
| Universal 40% fill rule | Cables above installed rating | NEC 392.22/392.80 or IEC 60364-5-52 grouping |
| Generic support spacing | Fitting failures at bends and tees | Manufacturer’s spacing including fittings |
| No expansion provision | Buckling, anchor pull-out | Joints at movement joints and specified intervals |
| Continuity via bolts only | High earth loop impedance | Bonding jumpers or listed bonding plates |
| No power/data divider | EMC problems, maintenance hazard | Metallic divider plus defined separation |
| Coating without thickness | Premature corrosion, claim disputes | ISO 1461 values plus corrosivity category |
| Depth without radius check | Cable damage at bends and drop-outs | Radius check against cable data |
| No fire-stop detail | Failed compartmentation inspection | Tested seal system for the tray type |
Application case: a warehouse distribution upgrade
Scenario constraints
An existing distribution warehouse is being re-equipped with a new conveyor system and additional lighting. The tray route runs 140 m along the roof structure, 40 m of it in an unheated loading dock open to the weather. Roof purlins limit support points, the ceiling void is 300 mm deep, and the client wants to add cables later without a shutdown.
Selection approach
The internal run was specified as hot-dip galvanised ladder tray at 55 µm minimum, with a 150 mm depth to accept the bend radius of the 4-core armoured feeder. The external dock section moved to a duplex coating — galvanised plus a topcoat — because condensation and road salt in an open dock exceed what a plain zinc coating handles in the long term. Support spacing was set from the load-deflection data at the actual purlin spacing rather than the catalogue default, and additional supports were added either side of each bend. A 30% spare fill was reserved by selecting one size wider than the immediate cable count, and a divider was included where the conveyor control cables share the route with the motor feeders.
Common mistakes on this kind of job
- Using the same coating specification indoors and in the open dock, then discovering corrosion at the dock within two years.
- Supporting from purlin clips rated for ceiling loads rather than for the tray load plus cables.
- Filling the tray to capacity at handover, leaving no route for the next cable.
- Ignoring the fire wall between the warehouse and the office block because the tray passes above the ceiling.
Acceptance points
Check coating thickness with a gauge at several points per length, including cut ends and welds; verify support spacing against the drawing at three random bays; confirm bonding continuity at the furthest point with a low-resistance ohmmeter; and inspect every penetration for a labelled, tested seal. For the external section, confirm the fall is continuous and that no section holds water.
Writing a specification that can be checked
- Name the product standard — IEC 61537 or NEMA VE 1 — and the installation standard, NEC 392 or IEC 60364-5-52.
- State the working load in N/m at the project span, not a class letter alone.
- State the coating system and the minimum thickness in micrometres.
- State support spacing, including the additional support required at fittings.
- State the earthing method and the maximum resistance to be demonstrated.
- State the fire-stop performance and the spare fill required at handover.
Incoming inspection and factory checks
On delivery, check the section against the drawing — thickness, depth, flange height, rung pitch or mesh size. Measure zinc thickness on a sample of lengths, including welded areas where coating is thinnest. Confirm splice plates and hardware match the tray finish, and that the load test report covers the span you are installing.
Assessing a cable tray supplier
Ask three questions. What is the working load at 3 m span for this product, and can you send the test report? What is the minimum zinc thickness on the section you are quoting? And what is your recommended support spacing at bends and tees? A supplier who answers from data sheets is quoting a product; one who answers from test reports is quoting a system. For projects near the coast or in chemical plants, add a fourth: what coating system do you recommend for this corrosivity category, and what is its expected service life?
Frequently asked questions
Is IEC 61537 the same as NEMA VE 1?
No. They cover the same product family but differ in load classification, test methods and marking. A tray compliant with one is not automatically compliant with the other, and a project should name the standard that applies.
What safety factor applies to cable tray loads?
Under NEMA VE 1 the tray is tested to a multiple of the working load, commonly 1.5 times, applied to the material yield strength. The manufacturer’s test report states the basis, and that is what should be quoted.
Can I mix power and data cables in one tray with a divider?
Yes, with a metallic divider and a defined separation distance taken from the EMC guidance for the project. The divider provides physical separation; it does not by itself guarantee signal integrity.
How often do I need expansion joints?
At every structural movement joint, and at intervals set by the manufacturer for the temperature range. For long external runs, calculate the movement from the coefficient of expansion and the design temperature swing rather than applying a fixed rule.
Does galvanised tray need additional earthing conductors?
The tray can serve as a protective conductor only where the system is designed and verified for it. Most projects run a separate CPC and bond the tray at intervals; the requirement comes from the installation standard and the earth fault loop calculation.
What tray type suits a food or pharmaceutical plant?
Generally stainless steel with smooth, cleanable surfaces and no open rungs where debris can collect, or a fully enclosed design. The washdown chemicals decide the grade, and the details — fixings, cut edges, seals — matter as much as the material.
How much spare capacity should be left?
Common practice is 25 to 30% spare fill at handover for a commercial or industrial installation, more where the client expects process changes. Reserving spare fill is cheaper than installing a second route later.
Get the specification reviewed before you order
BANGE Electric supplies cable tray and cable ladder systems for industrial, commercial and infrastructure projects, and can review a tray specification against the load, coating and earthing requirements before manufacture. Send us the cable schedule, the support arrangement and the environmental conditions, and we will tell you where the specification is undersized rather than simply quoting what is written. Contact our engineering team with your project details. Requirements may vary by application, market, and applicable standard.
