Trunk and Conduit Sizing Spreadsheet (Filling Ratio Calculation)

# Trunk and Conduit Sizing Spreadsheet (Filling Ratio Calculation)

The trunk is important in electrical system for buildings, it is an enclosure that provides for the protection of cables. It is normally square or rectangular in cross section and has a removable lid. The trunking system offers great flexibility when used in conjunction with conduit systems. It is the backbone or framework of an installation.

We provide you with an excel sheet that will help you find the suitable size for cable trunk and conduit, this will happen with the filling ratio formula.

Download also: Cable Tray Sizing Calculator and also: B Line Cable Tray Manual

### Types of Steel Trunking:

There are different of types of steel trunking such as:
• Lighting Trunking
• Cable trunking
• Multi-Compartment trunking
• Bus-bar Trunking

### Trunk sizing formula (filling capacity):

Trunking sizing depends on the following formula

N x Ac = F At
N* (Ï€Dc2)/4 = F*W*H

F: factor of occupancy, (taken 40%)
N: no. of similar cables inside the trunk.
Ac: overall cross section of data or tel. cable
At: overall cross section of trunk
Dc: overall outside diameter of data or tel. cable
W: width of trunk (mm)
H: height of trunk (mm)

### Conduit sizing formula (filling capacity):

depending on 40% factor of occupancy:

general equation:-

N x Aw = F Ac
N* (Ï€Dw2)/4 = F*(Ï€Dc2)/4

F:Factor of occupancy, (taken 40%).
N:No. of similar cables inside the conduit.
Aw:Overall cross section of cable.
Ac:Overall cross section of conduit.
Dw:Overall outside diameter of cable.
Dc:Overall outside diameter of conduit.