In electrical Systems for laying power cables , cable trays are
preferable mode for laying cables over a long distance where digging can’t be
feasible or digging cost is very high. Cable trays are also used where space is
low. Also cable trays gives aesthetic looks to electrical systems.

There are following recommendations for designing cable trays:-

1.
Always take 10-20% as
Spare capacity.

2.
Distances between cables
should be from 5 mm to 10 mm.

Now let’s illustrate the same by taking an example:-

Here we will design cable tray for aluminum cables:-

(i)
10 no’s 2.5 mmsq X 4 Core cables

(ii)
25 mmsq X 4 Core 10 no’s cables

__Total Outer Diameter :__

Diameter of 2.5 mmSq.mm Cable =No of Cable X Outer Diameter of
Each Cable

=10 X 16 = 160 mm

Similarly for 25 mmsq cables = 25X10 =250 mm

Total Diameter of All Cables laying in Tray = (160+250)mm= 410 mm

__Now Weight of Cables will be:__

Weight of 2.5 Sq.mm Cables =No of Cable X Weight of Each Cable

=10 X 0.56= 5.6 Kg/Meter

Similarly for 25 mmsq cable= 10X1.11= 11.1 Kg/ Meter

Total Weight of All Cables laying in Tray = (5.6+11.1) Kg/Meter=
16.7 Kg/ Meter

__Width of all Cables:__

Total Width of all Cables = (Total Cables X min. Distance between Cable)
+ Cable Outer Diameter in total

Total Width of all Cables = (20 X 5) + 410 = 510 mm

Now after taking 10% Spare Capacity of Cable Tray

Final Width of all Cables = 1.1X510 =561 mm

__Now total area of cables__

Total Area of Cable = width
of all Cables X Maximum Height Cable

Total Area of Cable = 561 X
25 =14025 Sq.mm

Taking 10% Spare Capacity of Cable Tray

Final Area of all Cables = 1.1X14025 = 15427.5 mmsq.

Now cable tray selected from above calculations is that either we
can install 1 no. 600 mm X 50 mm cable tray having weight carrying capacity of
50 kg/ meter, this cable tray has overall area of 30000 mmsq , Or we can
install 300 mm X 50 mmsq 2 no. s cable trays with area = 30000 mmsq.

We can even use single 300 mmsq X 50 mmsq cable tray and placing
one cable over another.

Usually perforated cable trays are used in electrical systems.