How to Calculate the Required FRP Cable Tray Width for Your Cables
Correct selection of FRP cable tray width is essential for safe cable routing, heat dissipation, maintenance and any future expansions. A too narrow tray will result in crowding, whereas a too wide one would be an unnecessary cost addition.
The general rule is straightforward:
Calculate the total space taken up by the cables, add the required margin, and pick the next available standard cable tray width.
But it is necessary to consider other factors as well.
What Determines FRP Cable Tray Width?
The required width is influenced by:
- Number of cables
- Diameter of individual cables
- Cable configuration
- Required spacing between different groups of cables
- Provision for additional future cables
- Type of tray
- Cable load
- Spacing of supports
For a single layer arrangement, cable diameters serve as a good starting point in determining the required width.
Step 1: Get the Outside Diameter of Each Cable
Do not calculate tray width using the conductor size alone.
Use the overall outside diameter (OD) of the completed cable, including its insulation and outer sheath.
You can normally find the cable OD in the manufacturer’s datasheet or cable schedule.
Step 2: Calculate the Total Cable Width
For the side-by-side installation of the cables in one layer:
Width of Cables = Total of Outside Diameter
For the example illustrated above:
Power Cables: 8 × 32 = 256 mm
Control Cables: 6 × 16 = 96 mm
Cable width total:
256 mm + 96 mm = 352 mm
Thus, 352 mm is the approximate area taken up by the cables before making provision for any design clearance.
Step 3: Add Allowance for Future Cables
It is quite common for industrial cable trays to have to cater for extra cables due to plant extension or change of machinery.
Rather than fill up the tray with cables during installation, provide an appropriate spare capacity according to the project specifications.
In case of 20% planning allowance:
352 × 1.20 = 422.4 mm
Therefore, the calculation provides for a total of about 422 mm.
It would be prudent to go for the next best available standard width of the tray instead of a 422 mm width.
If a 450 mm FRP cable tray is available and meets other design specifications, it would be sensible to choose it.
Step 4: Check Cable Separation and Segregation
The sum of cable diameter does not necessarily define the width of the cable.
In some installations, there is a need for segregation between various types of cables, such as:
- Power cables
- Control cables
- Instrumentation cables
- Communication cables
The space occupied by the segregation process is also taken into account during the design of the tray.
This is especially the case for industrial facilities where the various circuit types might use the same routing system for cables.
Step 5: Check the Tray Depth
Width is not the only criterion when choosing the tray.
The depth of the tray or its side walls should also be adequate to the arrangement of cables and the carrying capacity of the producer.
Thus, Plastic Fabricators offers solid bottom FRP channel trays in the following sizes:
50 × 50 × 3 mm
100 × 50 × 3 mm
150 × 50 × 3 mm
200 × 50 × 3 mm
300 × 50 × 3 mm
450 × 50 × 3 mm
500 × 100 × 4 mm
600 × 100 × 4 mm
FRP ladder trays by Plastic Fabricators come in the widths of 300 mm, 600 mm, 700 mm, and 900 mm with the side wall height of 100 mm.
So, once the required width is calculated, it is necessary to verify whether the chosen width × depth × thickness will suit the cable load and the span of support.
Step 6: Check the Cable Weight
Even though the tray might have sufficient physical size, it may still not be suitable if the cable loading is too heavy.
To find the total weight of the cables per meter,
Total Weight of Cable per Metre = Total Weight per Metre of All Cables
Also take into account the weight of the:
- Cables
- Tray
- Covers, where applicable
- Accessories
- Supported components, if any
The total weight will need to be compared with the capacity of the tray at the actual spacing of supports.
Technical assistance is available from Plastic Fabricators regarding FRP cable tray selection.
Worked Example: Selecting FRP Cable Tray Width
Suppose an industrial project has:
- 8 power cables with 32 mm OD
- 6 control cables with 16 mm OD
- 20% allowance for future cables
Calculation
Power cable space:
8 × 32 = 256 mm
Control cable space:
6 × 16 = 96 mm
Total:
256 + 96 = 352 mm
Add 20% allowance:
352 × 1.20 = 422.4 mm
Tray Selection
The calculated requirement is approximately 422 mm.
The next suitable standard width could therefore be:
450 mm FRP Cable Tray
The final selection should still be checked for load capacity, support span, cable arrangement, segregation and tray depth before the purchase order is released.
Should You Choose a 300 mm, 450 mm or 600 mm FRP Cable Tray?
| Cable Requirement | Possible Tray Width |
|---|---|
| Small cable bundle | 100–200 mm |
| Medium cable bundle | 300 mm |
| Larger single-layer bundle | 450 mm |
| Large cable grouping | 500–600 mm |
| Large power cable routes | 600–900 mm ladder tray |
These are preliminary selection ranges, not universal design rules. The final width must come from the cable schedule, installation arrangement and applicable project requirements.
Plastic Fabricators offer FRP cable trays from 50 mm to 900 mm wide, depending on the tray type.
FRP Cable Tray Width vs Cable Tray Fill
One must be cautious about not confusing the tray width with a universal “fill percentage.”
There are various standards and design codes that approach cable layout, fill percentages, spacing, thermal performance, and load differently. IEC 61537 mostly deals with the requirements and tests concerning cable tray and ladder systems and must not be mistaken for a universal cable fill percentage.
For this reason, it is better to rely on the governing electrical code and cable manufacturer’s information to determine the proper fill percentage.
When Should You Choose an FRP Ladder Tray Instead?
It is also not enough that the number of cables is used alone to determine the type of tray.
For example, the ladder type FRP cable tray can work best for large cables since the air can flow around the cables, which makes them easily accessible for inspection and for adding more cables later. The plastic fabricators use their ladder trays for power distribution and larger cables, while the channel trays for instrument and control cables.
Select the tray based on:
Type of cable + heat generated + protection required + installation + load
Common Mistakes When Calculating FRP Cable Tray Width
The use of wire size rather than cable OD
Always use the full cable’s OD.
Overloading of tray to its physical maximum capacity
Reserve sufficient capacity in accordance with the project design rather than overloading the tray.
Disregard of cable segregation
There are differences in routing of power, instrumentation, and communication cables.
Looking at width and not the load
A wide tray does not necessarily mean a strong tray.
Neglecting the need for expansion
Expansions often take place in industrial installations, so it needs to be taken into consideration in the design phase.
Choosing the tray first and then the cable schedule
Cable schedule comes first, then the tray width should follow the cable requirement.
FRP Cable Tray Width Calculation Formula
For a basic single-layer calculation:
Required Width ≈ OD of all Cables + Separation Distance + Provision for Future Capacity
Where:
OD of all Cables = ∑(Number of Cables × OD of Cable)
In the case of the solved problem:
Required Width ≈ (8 × 32 + 6 × 16) × 1.20
Required Width ≈ 422.4 mm
Choose the next appropriate size of tray and confirm the load capacity, span, depth, separation etc.
What Information Should You Give an FRP Cable Tray Manufacturer?
For an exact quote and technical recommendation, please provide:
- Cable schedule
- Quantity of cables
- Outside diameter of cables
- Weights of cables
- Required length of tray run
- Classification of power, control, or instrumentation
- Required segregation
- Span of supports
- Environment of installation
- Required type of tray
- Drawing or route drawing
Plastic Fabricators will also accommodate any special cutting, drilling, notching and other fabrication needs.
Final Takeaway
The calculation of the correct FRP cable tray size depends on the cable schedule you have, not the tray catalog.
Find out the total outer diameter of your cables, the needed space between them, and choose the most suitable standard tray size. Then, check the tray depth, the loading, cable segregation and installation requirements.
To get a personalized FRP cable tray suggestion, provide your cable schedule, cable diameters, routing distance, span and application specifics to the manufacturer.
How to choose the right FRP cable tray size? Send your cable schedule to Plastic Fabricators and we’ll suggest the correct FRP cable tray size and quote the price.