How to Size Power Cable Duct 

By on

Some colleagues had an issue earlier in the week on sizing ducts to be cast in concrete for some power cables .  It became clear that none of us had a clear idea on an approved method.  In the end we agreed that selecting the duct based on a 40% fill factor was a good idea.  This may not be the best approach.  If anyone has other ideas, please add below.

Using fill factor:

1. Required fill factor k (0.4 in our case)

2. Cable diameter Cd,  giving cable area, a:

6cc7ed63d44f12dcabb4486f27cd91fb

3. Cable total area Ca = sum of area for all cables

4. Minimum duct diameter  Cc:

3445e1acc7a26e6ea9a105c79abf241b

To make life a little easier, I have put together a cable duct sizing  tool which will do the arithmetic.

Once the calculation is complete, choose the next largest size of ducts.  What-if scenarios can also be carried out to optimize the quantity/size of ducts.  In a real installation, it would be good practice to have multiple ducts the same size if possible and put a couple of spare ones in as well.

In addition to determining the size of cable ducts and number of cables, we also need to think about the maximum number of cables in a duct.  The more cables, the more problems there will be with pulling (friction, bunching, etc.).  It seems a good thing to limit the number of cables per duct to five or less. 

This is a post that raises questions in addition to answers.  If you have any good ideas or tips on the duct sizing, please add below.  I'll add the good stuff into the post, so that over time we end up with a great resource. 



Steven McFadyen's avatar Steven McFadyen

Steven has over twenty five years experience working on some of the largest construction projects. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. About the author

myElectrical Engineering

comments powered by Disqus



Batteries

A battery consists of one or more cells, each of which use stored chemical energy to produce electrical energy, There are many types of cells and these...

How Electrical Circuits Work

If you have no idea how electrical circuits work, or what people mean then they talk about volts and amps, hopefully I can shed a bit light.  I’m intending...

Frame Leakage Protection

While not as popular as it once was, frame leakage protection does still have some use in some circumstances.  In essence frame leakage is an earth fault...

RLC Circuit, Resistor Power Loss - some Modelica experiments

Modelica is an open source (free) software language for modelling complex systems. Having never used it before, I thought I would download a development...

HTML Symbol Entities

HTML supports a variety of entity symbols which can be entered using either numbers or an entity name.  The number or name is preceded by the ‘&’ sign...

Induction Motor Calculator

Just added a page to the tools, which will allow you to calculate the synchronous speed, slip and rated torque for an induction motor. Not a particularly...

International System of Units (SI System)

The International System of Units (abbreviated SI) is the world's most widely used system of units.  The system consists of a set of units and prefixes...

Always Use PPE

A lot of our members work in countries where PPE (personal protective equipment) is regulated or they work for companies/organizations which take employee...

Earth Electrode Resistance

Earthing of electrical systems is essential for the correct functioning and the protecting of life and equipment in the event of faults.  The earth electrode...

How to Check a Circuit is Dead

If you want to check a circuit is dead (not live), you should always use the three point method. First check a known live circuit, then check the dead...

Have some knowledge to share

If you have some expert knowledge or experience, why not consider sharing this with our community.  

By writing an electrical note, you will be educating our users and at the same time promoting your expertise within the engineering community.

To get started and understand our policy, you can read our How to Write an Electrical Note