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

Trunk and Conduit Size Spreadsheet 

The following spreadsheet calculator will help you in trunking space factor calculation.

Download Trunk and Conduit Sizer Spreadsheet (Filling Ratio Calculation)

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* (πDc2)/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* (πDw2)/4 = F*(πDc2)/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.

Download also: Electrical cable sizing calculator

with the excel sheets you can find cable trunk and conduit sizes and the filling ratio for them, also you will find tables for cable types and sizes.