Thursday, May 27, 2010

Temporary electrical cabling

Today readers get to see a few pictures of bad practices in the utilization of temporary electrical supply at a building construction site.

Picture 1 – Temporary electrical panel

===== RELATED ARTICLES:  Temporary electrical installation pictures | Temporary electrical installation pictures  |   Temporary Electrical Earthing Pictures  |   Temporary electrical panel and cords pictures   |

About the author:

I got involved with this new building project since a few weeks ago.

After reporting to work at the construction site, I spent the first few days attending a few meetings and on the fourth day I took my first round of general inspection around the building under construction.

I went out alone on that first inspection, bringing with me my old and cheap Canon digital camera. It was really a cheap camera and that is probably the reason the picture quality here are not so good.

My previous digital camera was much better but it got stolen when my car was broken into.

First things first

The first thing that I look for when starting on a new project site is always the temporary electricity supply equipment and their associated temporary cabling and wiring works.

There can be hundreds of workers are involved during peak period of activities in a building job of a few million dollars.

With a bad temporary supply installation and with most workers being generally ignorant of the dangers of temporary electricity, the risk of fatal electrical accidents is always high.

I did my round and took a few pictures of temporary electrical panels being used, the temporary supply cabling, wiring, and extension cords that were taking supply from temporary panels.

I selected a few of the picture shots that I took and sent it to the Main Contractor’s Project Manager together with the following Site Memo.

You can see a few of the pictures of the temporary electricity supply DB and their cabling works toward the end of this post.


Dear Sir,

Re: Temporary electricity supply: Electric shock hazards

As I have explained on Saturday last week, please find attached photographs of the temporary electrical cabling.

I believe the photos are self-explanatory. However, I wish to highlight the following points:

Many extension cords do not have the grounding cable.

The extension cords are laid on the floor along main work traffic. Cables can be damaged leading to exposures of LIVE cables. A few have already been damaged and improperly patched up.

Observe that the area is a very wet area. The risks of electrocution here is very high.

I suggest the following action be taken IMMEDIATELY:

If possible, the temporary DB is relocated to a more suitable and DRY area.

Enforce the rules that all subcontractors run their extension cords at high level along walls or columns.

Enforce the rules that all extension cords have a working grounding conductor.
It is my opinion that the present situation is VERY DANGEROUS and a fatal electric shock accident can happen any time.


Lee Wan Seng
Resident Electrical Engineer

Picture 2 – Temporary electrical cabinet

Picture 2 above shows the overall view of the temporary electrical cabinet where the temporary electric panel is located.

I know that many electrical readers are surprised by the way I accept these equipments and installations.

The temporary panel in the pictures is not what I would use if I am in charge.

Here I was not in charge. I was the resident engineer representing the professional electrical consultant in a design-and-build contract.

In this type of contract, the main contractor is the boss and the paymaster.

And this project was in a “third world country".

We in the construction and engineering consultant industry cannot turn the standard of our construction practices overnight, especially not in the design-and-build or turnkey types of contracts.

What we can do is to set out priorities in an order that can still be implemented on the ground within a particular contract scenario.

In this case, it was an issue of safety of human lives.

Even in this matter of life and death of many human lives, priorities must be set properly so that it can be implemented.

I could have rejected the whole temporary electrical DB and the temporary cabling in the picture.

In many situations, I have done so.

However, in real life situations, political factors are always present and everywhere, especially where there is a lot of money involved. That is the nature of life that I know.

To say it simply, if I rejected the makeshift temporary electrical DB, I would have been kicked out of the project in a matter of a few weeks and the main contractor would have easily found a replacement that would bend to their wills.

Of course I could easily find myself another job, even with much better paychecks and benefits if I want to.

However, nothing good would come out as far as the electrical safety at this construction site is concerned. It may even get worse.

That is why I sent out the above Site Memo.

If the Main Contractor take action as I advised (which they did immediately after receiving the memo) in the above Site Memo, then I would have made a strong improvement. That was a good first step.

The point here is that handling construction issues on the ground has as much to do with diplomacy and PR works as with technical issues.

One has to properly balance a number of top priority matters in order to get things improved enough.

That is a measure of effectiveness of the site supervision team in the real construction world.

Going back to the reason I made this blog, its objective is mainly to share pictures. With this method, I share my experience with the readers. Good experience, and the bad ones.

You will find lots of pictures showing good electrical installations here. You will also find tons of bad installations. I am not recommending anything by showing all these pictures, unless I specifically say so.

As long as readers find some uses from the pictures, then I would have accomplished my purpose by sharing the pictures that I have in this blog.

Enough said. Now let’s get back to the pictures.

Picture 3 – A view of the wet area around the electrical panel

This picture shows one situation was with a wet area around the temporary panel and unsuitable extension cords laying around on the building's ground floor.

From the point of view of safety practices and regulations, I think this real life example has broken about all the relevant codes in the book.

Picture 4 – Damaged extension cord

This shows a closer view of the extension cords laying on the work floor. They have no armor and could be easily be damaged.

A few have been already damaged and improperly patched up.

Picture 5 – Closer view of the repaired extension cables

Picture 6 – One of the portable electric tools

Picture 7 – Extension cords on the floor

Picture 8 – An example of electrical plug without earthing connection

I wish to emphasize a little bit here.

Why do you think the workers did not connect the green earth cable to the plug?

The extension cord already has 3 cables one of which was meant for grounding.

So why such a reluctance to do it?

The reason is almost the same most of the time. The ELCB on the electrical panel may trip if the green earthing cable is connected.

Portable electrical tools used at construction sites are mostly motorized tools (e.g. Drills, grinders, electric hammers, etc).

These tools always have an electric motor underneath the casing.

An electric motor always has a coil that transforms the electrical energy into the mechanical energy that do the work.

That is where the problem comes from.

Motor coils have a tendency to leak electrical voltage. Other moving parts behave similarly also.

The leaked electric voltage (Note: an electric voltage is an electrical pressure much like a water pressure inside a water pipe) would turn into a leakage current if the electric tool is properly earthed or grounded.

The flow of the leakage current would be detected by the ELCB (earth leakage circuit breaker) unit on the electrical panel and the ELCB would trip.

If the grounding conductor is not connected as shown in Picture 8, then the ELCB would not trip. So the worker using the portable electric tool could keep on working.

In another word, frequent trippings of the ELCB is a nuisance to the workers.

That is why they disconnect the green grounding conductor of the extension cord.

But then, without the grounding cable, the worker has zero protection against the risk of electric shock.


Picture 9 – Grounding of the temporary supply through the steel wire armor of the multi-core armored distribution cable

That is all I have for today. See you again in the next post.

Copyright Temporary electrical cabling

Tuesday, May 18, 2010

Underfloor trunking pictures

The underfloor trunking system has been around for a long time. The first time I saw it was inside an application guide published by a public telecommunication company.

The technical manual was already very old and I was in the first year of real professional work after my graduation. That was 23 years ago.

Picture 1 – Underfloor service box installation in progress

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About the author:

Why do we need an underfloor trunking system?

An underfloor trunking system is an alternative way of providing the dedicated routes to run electrical cables, telephone cables or any other wiring cables you can think of.

I said wiring cables. An 11KV cable is not a wiring cable. A 25 electrical feeder cable to supply an 11 KW fire pump panel is not a wiring cable.

(Note: 25 means 25 millimeter square. It is a measure of the net cross-sectional area of the electrical conductors of an electric cable).

The 1.5 cables that are used for wiring the office lights are categorized wiring cables.

The 2.5 or 4 cables used in socket outlet wiring are also categorized as wiring cables.

That is on the electric power cables.

On the telephone side, the telephone wiring cables going to each telephone outlet in an office area are also called wiring cables.

But an incoming 100-pair telephone cable from the public telephone company into a multi-storey office building is not a wiring cable.

Likewise, a Cat 5 computer network cables going to the office computers from the server rooms can be called wiring cables.

However, a multi-core fiber optic cables connecting two computer buildings cannot be called wiring cables.

So those cables categorized as wiring cables can be run inside the underfloor trunking system.

In fact, the underfloor trunking has been invented specifically for this purpose.

Why the special treatment is given to the underfloor trunking?

Why not use the normal conduit and trunking? (See the conduit and trunking pictures here: Conduit installation pictures; Electric trunking pictures.)

The underfloor trunking system was developed long before I started my career in electrical engineering.

However, I think I can guess why there was a need for this system.

The need arose because of the popularity of open office layout system in the design of buildings.

There is no doubt that many residential buildings also use underfloor trunking systems. However, these buildings do not really have to use this system. The normal conduit and trunking system would serve the purpose perfectly well.

However, in an open office system, it is difficult to bring the wiring cables to the working tables in the middle of an office space (i.e. away from the walls) without running the cables inside the floor.

With many tables away from the walls, then many trunking and conduit need to be cast into the concrete floor.

Furthermore, different types of cables (eg. electrical and computer network cables) need to be run in different trunking and conduits totally segregated from each other.

In the end there were many trunking and conduit running all over the place inside the concrete floor slab of an office building with the open office concept of design.

So gradually the underfloor trunking concept developed, naturally.

Picture 2 – The underfloor trunking installation in progress

This picture shows a stretch of underfloor trunking installation in progress.

Notice that the floor reinforced concrete slab has been cast. The underfloor trunking was laid onto the already completed structural slab of the floor.

After the underfloor trunking components that need to be cast in have been laid out and fixed, a layer of concrete (called screeding) is poured to the floor to a thickness of about 50mm.

This additional two inch of concrete would cover the trunking parts, but the junction box would be exposed for access.

The thickness of the concrete screeding should be enough to give strength (and therefore would not crack) at the thinnest areas, which are the areas above the trunking parts.

Observe the notes that I gave in the picture.

During installation, there is always some time lapse between the installation pf the underfloor trunking parts and the pouring of the screeding concrete.

During this time, the trunking, junction boxes and service boxes need to be firmly held in place temporarily.

Steel bands and lean concrete are used for this purpose.

The temporary cover for the junction box opening is installed to prevent the fluid concrete from flowing into it during the concreting work. This temporary cover is made of soft metals and is usually supplied together with the junction box or the service box unit.

Notice also that there are three lengths of trunking installed together. So it is a 3-compartment trunking system. It could have been a 4-compartment or 2-compartment.

Here the trunking material is made of high-impact PVC trunking. However, an underfloor trunking can also be made of metals.

What is the difference between a service box and a junction box?

I should have explained this earlier so that beginners do not get confused.

A service box is a box along the underfloor trunking where the user can connect to the power outlet, telephone socket and computer socket.

It is the point of “service”.

Picture 3 below shows how a service box looks like.

Picture 3 – An underfloor service box

While a junction box is provided to facilitate the drawing in of cables during installation and maintenance.

It is also provided where a trunking need to make a bend and where it branches off.

That is why it is called a “junction” box.

Picture 4 – A completed underfloor junction box

Observe that the completed junction box cover is firmly fixed with 4 mounting screws at the corners.

On the other hand, the cover of the service box is designed so it can easily be open frequently.

That is because the service box is designed for user access. This is where users plug in their appliances just like the wall sockets.

Picture 5 – Vertical access box

The underfloor trunking resides at the floor. However, the cabling inside the trunking must come from the distribution panels somewhere.

If the distribution panel is located at the wall, then there must be a connection between the trunking inside the concrete floor and those at the walls.

That is the purpose of the vertical access box in Picture 5 above.

Sometimes, the electrical distribution panel is located inside the electrical riser which is some distance away. Usually the most convenient method of running the main trunking by hanger brackets above the ceiling.

Then at convenient locations, a set of droppers are installed to connect to the underfloor trunking. This is shown in Picture 6 below.

Picture 6 – Vertical access connection to trunking above ceiling

Picture 7 below shows another view of a junction box and underfloor trunking installation is progress, before the floor concrete screeding was poured in.

Picture 7 – Junction box and underfloor trunking picture

Construction works are never free from errors. Picture 8 below shows that a finished floor had to be hacked in order to extend the wiring from a junction box to the dry wall.

Picture 8 – Wall socket wired from an underfloor junction box

This was actually a last minute decision that was made to add another general purpose electrical outlet to the wall.

Theoretically it is best to wire general purpose electrical sockets on walls from separate circuits (better still, from a separate section of the busbar inside the electrical DB) than those inside the underfloor trunking, which supplies the work computers and other high priority equipment.

This is because the general purpose sockets are those used for such things as electric kettle, vacuum cleaners and other similar appliances.

Defects and faults in these appliances can cause trippings of the earth leakage circuit breaker (ELCB) at the electrical distribution panel, which can cause annoyances and other more genuine problems. (See pictures of ELCB at this post, 1-phase ELCB connection pictures.)

Update (March 15, 2014):
I have in my collections a lot pictures of materials that have been delivered to construction sites for installation of electrical systems.

For a long time this matter has been tickling my thoughts when I search through the pictures to attach to my posts.

Such a waste. These pictures has been helping me a lot of my work. Surely it must be of value to many people out there who still have no chance yet to get involved in actual electrical installation works.

Of course I can just upload all these pictures into the internet. But I don't think Google's search engine is smart enough to understand pictures and choose the right one for web users who are looking for them. There are probably trillions and trillions of pictures on the internet.

I cannot really make much of an article from pictures of electrical materials still in the plastic packings. It is too difficult. It seems too trivial, and I am not a much of a writer in the first place.

Today it just clicked in my head that I do not really need to write articles for these type of pictures. I can just attach the related one at the end of a related post. That's it!

I only need to write a few words to accompany each picture. The original post already says enough.

So with this revelation I am going to expand all of my posts to include a new section called "MORE RELATED PICTURES".

There I will gradually attach related pictures with a short description for each picture. I somehow a story clicks in my brain, then you will see a short story about the materials in the picture also.

If not, then just the description of the materials.


Picture 09 - uPVC duct materials for an underfloor trunking system installation

This is the first picture that I will attach to this post today.

If you observe carefully, the trunking material are still on back of the delivery truck.

These are 3 inch by 1 inch uPVC ducts if I am not mistaken. The picture was from one of my office building projects.

If you enlarge the picture, you may notice that there are water droplets on the materials.

Well, this is another aspects of electrical construction which is proper handling of materials and equipment during loading and unloading, delivery and storage.

In this case here, the delivery truck people did not seem to care enough to put the rain cover over the material.

This happen to be not an issue here because the uPVC material have not problem with rainwater such as this.

However, it was still not a proper way to delivery the materials to a client who pay good money for them.

One thing that I wish to say on this picture is that we should always witness the delivery, and unloading of materials to a project site.

There are many types of materials and equipment that can get damaged or deteriorate in quality considerable when not handles properly during delivery, loading / unloading, and storage.

If the damages are noticeable during inspection, then you only need to reject the materials or equipment. Then they can be returned back to the manufacturer or his supplier.

What if you did not notice anything and proceed with the certification for payment and later found out that the materials have been damaged?

They may be a difficult dispute over who caused the damages. I have been through this many times.

A manufacturer might say the materials have been damaged during the storage at the client's store.

Anyway, that is all I wish to say on this. I will upload other pictures the the underfloor trunking installation soon.

Copyright Underfloor trunking pictures

Monday, May 17, 2010

A simple electrical installation

Anybody looking for a layout and schematic diagram of a simple electrical installation?

Diagram 1 – Simple house electrical layout

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About the author:

This layout is very old.

At least 30 years old or more.

You can see that by the number of electric socket outlet in the bedrooms and the kitchen.

A modern bedroom would need at least a few sockets in each room. You would need one for the table clock, table lamp, a television maybe, etc etc.

One electrical socket as shown in the electrical layout would definitely be not enough.

Whereas in the kitchen there is only one, and one at the dining space. The one at the kitchen area was provided for the refrigerator.

So this design IS VERY OLD.

However, I believe there are still great many areas in the world that still lack even the basic supply of household electricity.

So this simple house electrical design is still useful to great many people.

In fact, this design is more relevant. It is also more easily understood.

The single line diagram in Diagram 2 below comes together with the electrical layout in Diagram 2.

Diagram 2 – A simple house single line diagram

This blog is for beginners in electrical works. The style used in Diagram 1 and 2 above is suitable for learners of electrical works.

I will not go into detail description of these diagrams today. I have already sent a few posts that contain detail descriptions on how to read schematic diagrams. They are scattered throughout this blog. You have to search around to find them. Sorry about that.

However, for genuine beginners, they may need to know which symbol means what in the electrical layout of Diagram 1. The meaning of the individual symbols is given in Diagram 3 below.

Diagram 3 – Schedule of legends and symbols

You can see more on electrical installation work by visiting this post, Electrical installation pictures.

Copyright A simple electrical installation

Sunday, May 9, 2010

Temporary electrical distribution

Would you believe it if I say that the picture below is a distribution system for a temporary electrical supply at a building under construction?

Picture 1 – A method(?) for a temporary electrical distribution

About the author:

I have been away for a few days. So I cannot write long posts yet.

Therefore, I will only give you pictures for a while. You have to interpret what they mean.

I took the above picture quite a while back. I thought I was interesting.

This distribution system was supplied from a temporary electrical panel nearby (see Picture 2 below).

Picture 2 – Temporary electrical panel

I was wondering why the worker needed to create such a distribution “harness”.

But I guess the answer was clear.

Notice the burn marks on one of the socket outlet at the temporary electrical panel (see Picture 3 below).

Picture 3 – Damaged electrical socket

A clearer view of the damaged outlet can be seen in Picture 4 below.

Picture 4 – Clearer view of the temporary socket outlets

You can see more pictures of electrical installations at this post, Temporary electrical installation pictures.

Copyright Temporary electrical distribution