Hello everybody, and welcome to a new post in our engineering Blog, “The Engineering Galaxy.”
In this article, I will discuss how to order the perforated cable tray, its fittings, and accessories.
But before that, I would like to give you a brief overview of the different types of cable trays based on their design concepts.
(i) Cable Trays Types:
A- Cable Ladder:
It has two main types, based on the shape and manufacturing of its steps: swaged, rounded tubular (Aluminum or Steel), or welded C-channel (Steel), as shown in the next photo.
It’s a prefabricated metal structure consisting of two side rails connected by individual transverse embers or rungs.
Cable Ladder Trays are the most common and economical type of tray.
They also provide maximum ventilation for cabling.
Usually, we use them with medium-voltage cables or main LV cables in the Transformer & Switchgear rooms.
B- Wire Mesh Cable Tray / Wire Basket Tray:
It is ideally suited for light-to-medium-duty commercial and industrial applications where space is at a premium. SFSP wire Basket Trays have a fast connection profile for installations requiring long runs of straight Cable Trays.
Applications: Network cabling, wiring closets, fiber to-desktop applications, and can often be used in suspended ceiling plenum areas and under computer room flooring.
We usually use this type for ICT/low-current systems, especially in structured cabling.
C- Solid Bottom Cable Tray ( Cable Trunk):
It’s a prefabricated metal structure consisting of a one-piece solid bottom channel section that usually does not exceed 6”(150mm) in width.
Usually, we use this type of tray with the final circuits like Lighting, Power, etc.
D- Perforated Cable Tray:
If you would like to learn about the different cable tray types, refer to the previous video.
It’s a prefabricated metal structure with a bottom featuring openings in the cable-bearing surface.
Solid-bottom Cable Trays completely eliminate cable sagging and provide maximum cable protection.
We mainly use perforated cable trays for low-voltage power cables.
To order the straight length of the perforated cable trays, you need to know:
1- The length of a straight piece of the perforated cable tray (L):
Usually, it’s 3 meters. Based on your full path of the cable tray route in meters, you will decide how many pieces you order.
For Example, if the route length is 269 meters, you need 89 pieces plus 1 more meter, so we will need 90 pieces.
2- The tray’s width (W):
It depends on the approved shop drawing based on the sum of the cables’ overall diameters. Either they exist or will be installed, taking into account the spaces between the cables.
3- The side height of the cable tray (H):
It depends on the maximum overall diameter of the cables in the tray. This is to ensure the tray’s side height can contain all the cables when you install the tray’s cover.
4- The thickness of the cable tray (T):
This depends on the total weight of the cables to be installed in the cable tray.
5- The material & finish of the cable tray:
It depends on the cable tray’s installation environment and its application, whether we will install it indoors or outdoors, or in a dry area or a wet area.
We have different types & finishes of cable trays, like:
– Aluminum.
– Pre-Galvanized Steel
– Hot-Dipped Galvanized After Fabrication
– Stainless Steel
– Fiberglass
6- The type of the return flange of the cable tray:
We have different types, like:
– Inside Type Return Flange, we will call it RFI
– Outside Type Return Flange, we will call it RFO.
– C Type inside, we will call it CTI.
– C Type Outside, we will call it CTO.
7- Type of perforation:
This is not an important topic, but you can find it in the manufacturer’s catalog.
Generally, we have two types of perforation: staggered and serial.
(ii) Cable Trays Installations:
First, to install these trays, you need a support system.
The support system will depend on the type of installation: suspended in the concrete slab, installed on a wall, or installed on a floor.
- For the installation type suspended in the concrete slab, we will need to use the following:
– Stud in anchor or unifix, we will install in the concrete slab to hold the threaded rods with complete support
– Threaded rods are galvanized rods that are threaded to fit inside the unifix.
– Flat Washers
– Hexagonal Nuts
– C-Channel, or slotted channel, usually has two common sizes, either 41x41mm or 41x21mm
A hexagonal rod coupler will be used if the support is longer than the threaded rod, so we will use it to connect the two threaded rods.
Notes:
1- From the previous installation detailed drawing, we can see that for each support, we will need to use (2 unifix+2 threaded rods+6 flat washers + 6 hexagonal nuts+1 piece of Unistrut C-channel).
2- The diameter of the threaded rods, unifix, flat washers, and nuts will depend on the weight of the tray with the cables installed inside these trays and the distance between every two supports.
Now I will talk about the most common fittings to be used with the perforated cable trays during the installations on-site:
01- Side coupler
We are using it to connect two pieces of cable tray or to connect the tray to any other fitting.
02- Fishplate
It will be used with the perforated cable tray. We install it to connect two pieces of the perforated cable trays from their bottom inner sides.
03- Braided copper connector (Tinned Copper Flexible Braids)
It will be used as an earthing link to ensure the entire cable tray route is already earthed.
04- Roofing bolts
We are using them to connect the cable trays with side couplers, the cable trays’ fittings and side couplers, and so on.
05- Tee Connections, either Equal or non-equal
We are using them in case we have three branches of the cable trays.
06- Horizontal 90-degree bend connection.
We use it when the tray’s direction is rotated horizontally by 90 degrees.
07- Horizontal 45-degree bend connection
We use it when the tray is rotated 45 degrees horizontally.
08- Intersection or Cross Connection, either Equal or non-equal (4 Ways)
We use it when we have four branches of cable trays.
09- Reducer
We use it when the tray size is reduced. Usually, this case occurs at the endpoint of the trays when we need to feed a final load, such as a disconnect switch, an isolator, or a Panel, and so on.
10- Internal riser
We use it when the cable tray routes run from a lower level to an upper level.
11- External riser.
We use it when the cable tray runs between an upper and a lower level.
12- Cover
You can understand its purpose from its name: we use it to cover the cable tray and protect the cables inside.
13- Spring nut
We use it to connect the cable tray and the unistrut channel.
14- Wingnut
It has the same function as the spring nut, but this type has wings on its sides.
Also, if you would like to read more about the various electrical tools used by electricians, please check this post here.
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