Cable Tray Selection for Fire Cable
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
Calculation:
For calculations
following Table is used:-
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.
 |
| Fire Cable Tray |
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.
