Views: 0 Author: Site Editor Publish Time: 2026-09-29 Origin: Site
Quick answer: A cable tray's load capacity is not a single number. It is the maximum uniformly distributed load (kg/m or lb/ft) the tray can carry at a specific support span, with deflection kept within a set limit. Change the span and the safe load changes with it. To select a tray, add up the cable weight per meter, then choose a tray whose tested rating covers that load at the span you plan to use.
Load capacity describes how much weight a tray can safely carry between two supports. It is always stated together with a span. A tray rated at 100 kg/m on a 3 m span does not carry 100 kg/m on a 6 m span.
Three terms appear on almost every datasheet:
Working load (or safe working load, SWL): the load the tray is designed to carry in service.
Support span: the distance between two adjacent supports (brackets, hangers, or trapeze).
Deflection: how much the tray sags under load, measured at mid-span.
NEMA VE 1 uses a two-part code. The number is the support span in feet, and the letter is the load rating per foot.
Letter | Load rating (lb/ft) | Load rating (kg/m, approx.) |
|---|---|---|
A | 50 | 74 |
B | 75 | 112 |
C | 100 | 149 |
Number | Support span (ft) | Support span (m, approx.) |
|---|---|---|
8 | 8 | 2.4 |
12 | 12 | 3.7 |
16 | 16 | 4.9 |
20 | 20 | 6.1 |
Example: A tray marked 12B is rated for 75 lb/ft (about 112 kg/m) on a 12 ft (about 3.7 m) span.
IEC 61537 takes a different approach. The manufacturer tests the tray on a stated span and reports the safe working load in N/m or kg/m. Results are typically published for several spans, such as 1.5 m, 2 m, and 3 m, so buyers can compare the same product at different support distances.
For a tray under a uniform load, deflection grows with the fourth power of the span. In practice, that means:
Cutting the span in half reduces mid-span deflection to roughly one-sixteenth.
If deflection limits the design, the allowable load falls roughly with the cube of the span.
If strength limits the design, the allowable load falls roughly with the square of the span.
These are rules of thumb for understanding the trend. Always use the tested load-span data for the specific tray, not an estimate.
Example data for our trays【replace with your own test results】:
Safe working load of our cable trays at 1.5 m support span
Model | Width × Height (mm) | Thickness (mm) | Safe working load (N/m) | ≈ kg/m |
|---|---|---|---|---|
WA-CT-5050-1.0 | 50 × 50 | 1.0 | 500 | 51 |
WA-CT-10050-1.0 | 100 × 50 | 1.0 | 600 | 61 |
WA-CT-100100-1.0 | 100 × 100 | 1.0 | 800 | 82 |
WA-CT-150100-1.0 | 150 × 100 | 1.0 | 900 | 92 |
WA-CT-200100-1.2 | 200 × 100 | 1.2 | 1000 | 102 |
WA-CT-200150-1.2 | 200 × 150 | 1.2 | 1200 | 122 |
WA-CT-300100-1.2 | 300 × 100 | 1.2 | 1500 | 153 |
WA-CT-300150-1.2 | 300 × 150 | 1.2 | 1600 | 163 |
WA-CT-400100-1.5 | 400 × 100 | 1.5 | 1700 | 173 |
WA-CT-400150-1.5 | 400 × 150 | 1.5 | 1800 | 184 |
WA-CT-500100-1.5 | 500 × 100 | 1.5 | 1900 | 194 |
WA-CT-500150-1.5 | 500 × 150 | 1.5 | 2000 | 204 |
WA-CT-600100-2.0 | 600 × 100 | 2.0 | 2050 | 209 |
WA-CT-600150-2.0 | 600 × 150 | 2.0 | 2100 | 214 |
WA-CT-800100-2.0 | 800 × 100 | 2.0 | 2200 | 224 |
WA-CT-800150-2.0 | 800 × 150 | 2.0 | 2250 | 229 |
WA-CT-800200-2.0 | 800 × 200 | 2.0 | 2300 | 235 |
WA-CT-1000100-2.5 | 1000 × 100 | 2.5 | 2400 | 245 |
WA-CT-1000150-2.5 | 1000 × 150 | 2.5 | 2450 | 250 |
WA-CT-1200100-2.5 | 1200 × 100 | 2.5 | 2500 | 255 |
WA-CT-1200150-2.5 | 1200 × 150 | 2.5 | 2550 | 260 |
WA-CT-1200200-2.5 | 1200 × 200 | 2.5 | 2600 | 265 |
What Deflection Limit Should You Use?
Deflection limits differ by standard and by project specification. Typical practice is to keep mid-span deflection to a small fraction of the span, with the tray returning to its original shape after the test load is removed. Check the deflection criteria in the standard and in your project specification, and confirm the figures against the current edition.
List every cable that will run on the tray, with its weight per meter from the cable datasheet.
Add the weights to get the total cable load in kg/m.
Add allowance for future cables. Many projects add 20–30% spare capacity.
Choose the support span based on the building structure and support spacing.
Find a tray whose tested rating at that span is equal to or greater than your total load.
Check the accessories: brackets, hangers, and splice plates must also carry the load.
Place splices near the supports, not at mid-span, where bending is highest. A common guideline is to keep splices within a quarter of the span from a support.
Use shorter spans at bends, tees, and risers, where loads concentrate.
Do not rely on the tray as a walkway or a lifting point unless it is rated for that.
Account for thermal expansion on long straight runs, especially outdoors and on solar sites.
Larger cables need a larger bending radius; leave enough room at fittings.
For long spans and heavy power cables, ladder tray usually delivers the best strength-to-weight ratio. Perforated and trough trays suit lighter or more sensitive cables and give more cable protection. See our comparison of [Cable Tray vs Cable Ladder] and [Wire Mesh vs Perforated Cable Tray] for details.
What does 12B mean on a cable tray?
Under NEMA VE 1, 12B means a 12 ft (about 3.7 m) support span and a load rating of 75 lb/ft (about 112 kg/m).
Does a longer span reduce load capacity?
Yes. As span increases, deflection rises rapidly, so the load the tray can safely carry falls.
What is the difference between working load and ultimate load?
Working load is the load for normal service. Ultimate load is where failure occurs, and it is higher by a safety factor set in the standard.
How do I calculate the load on a cable tray?
Add the weight per meter of every cable on the tray, then add allowance for future cables and compare the total with the tray's rated load at your span.
Can I use one support span for all tray widths?
No. Wider or deeper trays and different thicknesses have different ratings. Always check the data for the exact model.
Where can I get test data for your trays?
Contact us with your tray size, cable list, and span. We will supply the load-span data and a recommendation.
Whatsapp: +86-18823394830 
