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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Conduit to trunking connections

I attach here a few pictures showing the connections between electrical conduits and trunking. Some few weeks ago a reader left a message on one of my blogs asking how to connect a branch conduit to a steel trunking. So these pictures should be self-explanatory enough how to make the connection.

Picture 1 – Electrical and mechanical services above the ceiling of an office building

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The above picture shows some of the services inside the ceiling space of and office building.

Here you can see some conduit and trunking works. For large office floor space, conduit alone is usually not enough to contain the wiring cables from the floor distribution panels to the lighting and power points.

However, it not practical and a sheer waste to use trunking up to a final circuit point, a light point for example.

A lighting point needs only three wires of 1.0 mm.sq. or 1.5 mm.sq. to make a complete wiring. This does not need a trunking. It is also difficult to connect a trunking to a lighting fixture.

Therefore, the wiring to the lighting point needs to be routed into a conduit. The best is flexible conduit.

The following two pictures show how a trunking branched into rigid and flexible conduit.

Picture 2 – Conduit branching into rigid metal conduits

The above shows two branches into rigid steel conduits. One using a circular draw box as an adapter, and the other is connected directly to the metal trunking without any drawbox.

Either one is fine, but if you have a number of circuits to be run into the branch conduit, then using the draw box might me more preferable. It would ease the work of drawing the wire.

If the tap off needs to supply only one lighting point, then you can save one draw box by connecting the trunking to the conduit directly.

Another reason for using the draw box is when the conduit do not connect to the trunking at 90 degree angle to the connected side. In that case, you definitely need the draw box.

In any case, the conduit and trunking works is a skilled tradesman’s work. Often many aspects of the actual installation tasks require some creativity and experience to do it properly at a reasonable cost.

If some tradesman have a long list of better ways to do this connection than the ones that I show in this post, then by all means follow him.

What I show here are those that are usually practiced locally here.

Picture 3 – Another two connections at the same location

One more important aspect of the connection between the electrical trunking and conduit is how exactly to fix the two pieces of electrical container.

It is not visible how it is done from the above three pictures. I also keep forgetting to open up an electrical trunking and take the picture of the connection inside the electrical trunking.

The third piece of the component that makes up the connection is only visible from inside the trunking which I presently do not have any picture.

However, there is one place where it is easier to see that third component. It is at the connection between a rigid electrical conduit and the concealed metal box of a socket out or a wall mounted light switch. The pictures below show this quite clearly.

Picture 4 – Connection between rigid electrical conduit and a concealed metal box

I have labeled the relevant components so you can see clearly what are involved in the connection between the conduit and the concealed box.

The “copper bush” is the component that I wish to show you. It is this same component that is used between conduits and trunking. When the conduit and trunking are made of metal materials, the “bush” is usually of copper material. This provides a good electrical connection between the conduit and the trunking.

On the other hand, if the conduit and trunking are of plastics or PVC materials, which are also quite commonly used in certain types of electrical installations, then the “bush” would be made of plastic or PVC.

The functions of the copper bush are three fold: one is to keep the connection firm and strong. The second is to provide a smooth finished that would not injure the insulation of wiring cables when they are drawn through the joint or connection. Lastly it serves to provide a good electrical continuity between the trunking and the conduit.

The following three more pictures give more view of the copper bush.

Picture 5 – A closer view of the copper bush in Picture 4

Picture 6 – Copper bush at another lighting switch with some wiring being installed

Here I use a picture that has some wiring already drawn in to show you how wiring cable can be damaged if the area around the connection is not smooth enough.

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Electrical Services Color Codes

The following set of pictures gives some examples on the identification of the different electrical services inside a building.

Picture 1 – Example color codes for a few electrical services

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The three conduits with the color code bands in the above pictures are part of what we call in building works as electrical services.

However, electrical services are not the only ones that require some means of identifying what they are for.

Mechanical services also really need their piping, trunking, etc to be provided with some identification.

In some installations such as hospitals, there are so many services under the mechanical category. At certain locations in a hospital complex, it is almost impossible to know which pipe is for what. (Remember that an electrical G.I. (galvanized iron) conduit is just a metal pipe.)

During maintenance, long after we the construction people have completed and commission the building with all the mechanical and electrical services fully tested and operational, the maintenance people could be cursing us every week for not providing sufficient identification for each of the services inside the building.

During operation and maintenance of the building, insufficient identification on each of the services throughout the building can lead to serious accidents.

Why do I talk about mechanical services? Because they often run along the electrical services. Now and then the parts and materials between the two disciplines look and feel just the same.

A note for the beginners: the different colors of the wires to a three-phase motor or to a machine that use three-phase power supply is a form of color coding.

Now let us get back to the pictures: In Picture 1 above you can see three conduits with color bands on them.

The one the right side (nearer to the concrete wall) has got a six-inch band with two colors. Or you can call it three bands with the outer two in red and the center band in white.

This conduit is for one of the Extra Low Voltage services. It is for the audio-video cables. An example where you can find this would be a large meeting room or a conference room, or an auditorium.

These types of building spaces would usually have conduits and/or trunking to contain and protect the wiring cables to and from the microphone points, the speaker points, ceiling speakers, etc.

That is an example of what we call an Audio-Video system.

(Note: Extra Low Voltage (ELV) Services is a name usually used to categorize some electrical services. Examples may be the Audio-Video system I have just explained above, security systems like CCTV and card access systems, queue management system, etc. These systems are still electrical systems because they still run on voltage and currents to say it simply. However, they use very low voltages of less than 25 volts anywhere in their equipment and wiring.

Of course they still need to connect to the 240 volt building electricity in order to work.)

The purpose of the color bands is simple: to identify what system the conduit is part of.

Table 2 below show a table of the ELV services in a building with the respective colors of the bands shown.

Not all buildings use the same colors, but large organizations usually have some sort of standard color coding system that must be followed by all contractors that execute work under the control of that particular organization.

Table 2 – Table of color codes for ELV services



Note that the colors for electrical conduits and trunking are not listed here. As far as I know it is a general practice everywhere to use orange as the color code for those electrical conduits, trunking and cable trays, while the cable ladders are more often not painted.

The subject of color coding is simple so I am not going to drag this post any longer than necessary. Readers can just scan through the other pictures below.

Picture 3 – Labeling on electrical trunking

Any building of a signification size usually has a supply source backed by standby diesel generators. This supply is usually called “ESSENTIAL SUPPLY”. The label “ESS” spray-painted below the smaller trunking is used to convey that message.

In office buildings, a form of centralized UPS (uninterruptible power supply) may also be provided. In Picture 3 above, the trunking that carries the wiring to all 13A wall sockets backed a UPS supply has been labeled “UPS”.

Please do not underestimate the importance of these labels. When the electricity supply from the public mains has failed, the standby diesel generators kick in. So the cables and wiring that run inside the ESS trunking is LIVE.

That means all socket outlets supplied from this trunking is still live and DANGEROUS.

The UPS unit always takes supply from electrical boards backed by the generators. So the wiring inside UPS trunking are also just as dangerous.

If the standby diesel generators also fail to start, then the wiring inside the ESS trunking has no power and not live.

However, the wiring inside the UPS trunking still has power because they are backed by batteries of the UPS unit.

Picture 4 – Another picture of electrical trunking

Picture 5 – CCTV conduit



Pictures 6 – Conduits for some other ELV services. You can check against Table 1



Picture 7 – CCTV conduit also



Picture 8 – Audio-video system



Picture 9 – This is another method to label the ESS supply




Okey folks… I need to get back to my work. See you again the next time.

Visit this post, Electrical installation pictures, to see more electrical pictures.

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Electric conduit installation pictures

You will find a number of installation pictures of electrical conduit in this post. I will not be writing much today, so this post will only present pictures.

Picture 1 – Surface run conduit



=================  RELATED ARTICLES: Underfloor trunking below structural rebars | MATV trunking riser |  Lighting flexible conduits |  Conduit to trunking connections |  Cable ladder pictures | Electrical conduits and trunking pictures | Electrical panel under water pipes  | Electrical busduct installation pictures   | Electric trunking installation pictures  | Electric Panel Installation Pictures  | FR electric cable installation pictures  | Multi storey building electric closets  | Underfloor trunking pictures  | Site-fabricated electrical trunking  | Electrical Services Color Codes  | Light switch installation pictures | Electrical installation pictures

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What you see here are surface run conduits inside a fan room of an office building.

For some reason that I do not know, personally I like surface run conduits, trunking, etc.

I also like to see things exposed like the exposed structural elements of a covered stadium.

Being able to see the things myself make me feel comfortable.

In the case of these conduits, having them exposed on the wall like that leave no room for any contractor to play with their tricks.

There is no doubt that concealed conduit works help keep the electrical system away from interference and possible accidental damage.

This is important where the space is a public space like a public corridor of a building.

Residential buildings are also not a good place to use surface run conduits like shown in the picture, even though surface run wiring (without conduit) used to be a standard practice in house wiring.

Why do we need these conduits?

The conduits are used to protect the wiring cables that carry the electrical current.

Electricity is dangerous. Even though the electric conductors that carry the current is insulated by some PVC covering materials or whatever, the covering material is not strong enough to protect the cable from damage.

When the covering is damaged, the electrical conductor inside may be exposed to touch or it can also unintentionally come into contact with things that can carry electric current.

This scenario would present a high risk of electric shocks.

Therefore, we protect the electric cables so that they do not present the dangers of electric shocks to people (or animals).

A second reason to protect the cables is to make sure the electrical system stays reliable.

When the cable PVC covering is damaged, the conducting metal can come into contact with other metals that are in contact with earth.

When this happens, the leakage protection of the electrical system will automatically trip the circuit breaker controlling the circuit whose cable has been damaged.

Damaged electric wiring cables can cause this tripping at time we need the electricity most.

Therefore, electric conduits are used to provide this reliability.

Picture 2 – Conduit connection to light switch concealed box



This picture shows how the electrical conduits are connected to the metal boxes.

These boxes are installed to house the rear of wall-mounted light switches. A 13A switched socket outlet mounted flushed to a wall would also have this concealed metal box.

The purpose of the box is to provide a protected space for the wiring cables from the conduit. This space gives enough room for the cables to maneuvers before terminating at the light switch or the socket outlet.

The space also provides the room for the rear portion of a switch unit to sit in.

With this method, we can change a switch unit when it is damaged without disturbing the wiring system too much.

Note the four screw holes already provided by the metal box.

Now, when the electric conduit is cut to suit height of the box, there may be sharp edges at the conduit end. These edges may damage the PVC insulation covering of our wiring cables.

A careful workmanship can easily trim the sharp edges, but controlling workmanship is not easy.

That is why a copper bushing is provided as you can see in the picture.

The bushing also helps to give good contact between the metal box and the metal conduit.

Did I forget to say that these conduits are made of metal?

They are actually galvanized steel conduit.

You can use the cheaper PVC conduit for the same purpose if you like. In that case, you may still use a suitable PVC bushing but not for the purpose of providing e good electrical contact.

The conduit in picture 2 is a concealed conduit for a dry wall partition. So the metal box is a concealed box.

Picture 2Picture 2a below show connection of sufrace conduit to a supface mounted switched socket outlet. The same method of conduit to metal box connection is required here except that the metal box is exposed so it it is a different design.

Picture 2a - Conduit connection to surface mounted 13A switched socket outlet



Picture 3 – Conduit saddle picture



When a conduit is installed exposed like those in Picture 1, it may sag if the distance between two supports exceed certain distance.

An electrical conduit must be installed rigid, permanent and without sag. It should also be able last with integrity for the design life of the building.

What if the building can last 100 years? Should the conduit installation be able to last 100 years also?

Well, if it can, then that is good. However, a wiring system will not be good enough 50 years from the time the building is constructed.

Technology change, how people use electricity change, the personal taste and preference of the people occupying a building space also change. All this will result in the need to renovate the building, and most likely the wiring system also.

The conduit system would not need to last 100 years.

However, it should be able to last 30 years. This is my opinion.

Therefore, once installed, the electric conduit should be rigid, permanent and strong.

In order to satisfy that, electrical installation specifications usually specify the maximum distance between conduit saddles. Some say 900 mm, some say 1100 mm.

The size of the conduit, the materials and the installation environment also are among the major factor in determining the maximum distance between the support saddles that is allowed.

The distance for the orange electrical conduit (the red painted conduit carried fire protection system wiring, not electrical cables) in Picture 1 is around 1.1 meters.

I am guessing only here.

I did not really check the distance. It looked reasonable when I was supervising the job. However, the specifications asked for 900 mm maximum for a one inch diameter conduit, if I remember correctly.

Do not quote me on this. If you are supervising a job, check your own specifications.

If you are doing your office wiring on your own, just keep the saddle spacing to 1000 mm.

Picture 4 – Draw in box



Some people call this a junction box; draw in box, or outlet box.

Whichever name you prefer, this component allows the electrician to draw in cable into the conduit a short length at a time.

If one tries to pull wiring cable into a conduit for too much distance in a single shot, he may find it very difficult to get the job done.

In real installations, the routes available for conduit installation are not straight all the time. There are bends and turns. These bend and turns plus the cable friction with the conduit interior make it hard to pull the wiring cables.

Forcing it too much may damage the cables permanently.

By practice, a maximum of 9 meter distance between draw in boxes on straight run conduit has proved to be practical enough for most wiring works.

If there are bends, then the box should be installed after every two bends.

Okay folks. That is all the time I can spare today.

See you in the next post.

P/S : You can see more pictures at this post, Electrical installation pictures.


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