Tuesday, January 24, 2012

Lighting flexible conduits

Why do we need flexible conduits for the wiring to lighting fixtures?

Picture 1 – A lighting flexible conduit above a false ceiling (Click on the image to enlarge it)

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Conduits provide the mechanical protection for electrical wiring cables that are run inside them.

Without this protection, sooner or later the wiring cables are liable to get damaged which can expose the live conductors that can lead to electrical fires and risks of electrical shocks.

Picture 2 – Rigid metal conduits running on surface below the concrete slab

(Click on the image to enlarge it)
As shown above, the rigid metal conduits are clipped directly to the concrete slab. This method allows for easy adaptation of the conduit run so that the end of a rigid conduit can be installed directly to the exact location of the light fixture, or directly above it.

If the light fixture is also surface mounted similar to that in the picture below, then the rigid conduit can be run directly to the light fixture.

Picture 3 – Rigid conduit direct connection to a light fixture

(Click on the image to enlarge it)
This installation is inside a plant room. So this method of installation can be done easily.

However, when an installation is above a false ceiling, as they usually are in large office buildings, then it is not really practical to run the rigid conduit directly to the light fixture because there is usually a significant distance between the surface of the concrete slab and the level of the false ceiling is obvious in Picture 1 above.

Well, to be precise, it can actually be done but in large installation works this method demands a very close control of the workers and slows down the speed of installation.

To say it simply, it cost too much extra while not adding anything of real value.

The practice is to use a length of flexible conduit to protect the wiring cables between the end of the rigid conduit and the light fixture as shown below.

Picture 4 – Flexible conduit connections to ceiling-recessed down lights

(Click on the image to enlarge it)
I know you cannot see the concrete slab in the above picture but together with the flexible conduit in Picture 1 you should be able to see the connection.

From the way the flexible conduits sagged vertically downward, you know the ends of the rigid conduits are directly above them.

However, I did not write this post just to explain to the above use of the flexible conduits.

Look at the following picture:

Picture 5 – Excessive length of flexible conduits

(Click on the image to enlarge it)
However, life is never simple.

This is especially true for construction works, and it is also true for the design works that precedes the construction.

In many cases, the layout design of the office (Note: I just pick office buildings as an example. Other types of buildings can suffer exactly the same type of problems) cannot be finalized on time for some reasons. This drastically affects the work of the electrical contractor who needs to run the conduits for the office lighting system.

In fast track projects, or design-and-build types of contract, postponing the conduit installation works just because the architects or the building owner need more time to finalize the office layout design (or to make another “minor” revision to the “final layout”) is not a good idea and a very risky one for the electrical contractor.

The wisest choice is usually to just proceed with the installation of the rigid conduit works based on whatever construction drawings available at the time.

Of course after completion you may get installation works that look like Picture 5 above.

Definitely not a good job, I agree with you. However, as some people say, it “still fits the purpose”.

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Isha Rana said...

I really enjoyed this. You can see in your article comments. This information has really been helpful for most of the readers. Electrical in Pune

The crusader said...

So does it mean in most of the projects, rigid metal conduit is laid below concrete slab..?
But I have seen in GCC (Saudi in particular) projects that the red color pvc conduits are laid while poring concrete itself. So which method is perofessional and effective..?

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