Wednesday, August 18, 2010

Underground electrical manhole

The picture below shows an electrical manhole intended for underground installation being unloaded from the transport truck.

Picture 1 – The electrical manhole being unloaded

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About the author:

Most building works require at least one or two underground electrical manholes. That is because a building of significant size usually require a few hundred amperes of electric current at low voltage (i.e. 240 volt, 3 phase current).

Above a few hundred KVA (kilo-volt-amperes), the electricity supply authority usually delivers the electrical power to the consumer loads at higher than 240 volt, usually at 11,000 volts.

(Note: 100 amperes x 240 volt x 3 phases = 24,000 VA x 3 phases = 72,000 VA = 72 KVA. For readers who are intimidated by the KVA term, this is what KVA is. That is measure of electrical power delivered to a building. It is also the most common unit used in specifying the size and rating of electrical equipment and switchgears.)

Okay, back to the electrical manhole.

When the supply is at 11,000 volts (i.e. 11 KV), high voltage cables installed below ground level (i.e. underground) is the most popular method of electricity distribution unless the building is in remote areas such as the countryside.

So, in building works, we need at least one or two of these manholes to bring in the authority cables from outside the boundary of the building works to the electrical substation inside the building compound or the inside the building itself.

Picture 2 – The electrical manhole at a closer look

Notice the note I put in the picture saying “precast conduit sleeves”.

These sleeves were made in the factory to facilitate the connection of underground electrical conduits carrying the cables to the manhole.

If these openings on the concrete walls of the manhole are not made in the factory, then the openings have to be manually made at site using electric hammers etc.

Most of the times, some modifications are still needed because the high voltage cables are usually large and they are difficult to turn and bend.

The underground conduits may also not arrive at the manhole at the same levels of the precast sleeves. If they do, they may not all be at exactly 90-degree angles to the manhole walls.

This means some hacking still need to be done to the precast sleeves.

I forgot to tell you that the precast sleeves are made to accept 150 mm diameter of electrical conduits. It is a common practice to use 6 inch diameter underground conduits for electrical distribution cables.

Smaller sized conduits are also used, but they are generally for underground street lighting cables and compound lighting cables inside the building compound.

In these cases, 4 inch diameter conduits are used and they are installed when the compound lighting cables need to cross under internal roads.

I did not mean this post to be discussing underground cabling works. I just wanted to show some pictures of electrical underground manholes so that I can just refer to this post when talking about underground electrical manholes.

However, the above brief issues on the manhole are necessary to give some meaning to the pictures here.

So for the readers with more advanced knowledge on these things, please be patient with me. This blog is for beginners.

Picture 3 – An installed underground electrical manhole

This is how it looks after the manhole has been installed. Even though it is called “underground”, the manhole is not really totally “buried” below ground.

The exposed part of it is still visible and accessible at ground level.

Picture 4 – Manhole cover

This is the top of the electrical manhole, which is leveled to the finished ground level, exposed and accessible for access.

Observe carefully that there are 4 pieces of the manhole cover. These covers are made of reinforced concrete. So they are very heavy. Breaking it into 4 pieces make it easier to be opened by manually hand-lifting it.

Even at that smaller-sized, it usually takes at least 2 normal-sized persons to lift open a single piece after a few years. Yeah. I know. Hulk Hogan may only need two fingers to do it).

Picture 5 – The base of the manhole pit

You cannot just dig a hole of sufficient size in the ground and plant in the concrete electrical manhole.

If you do that, sooner or later one of the manholes would sink in deeper into the ground, or get tilted enough to break the underground electrical conduits and possibly damaging the underground cables.

When that happens, you would then need to carry out excavations when one of the cables need repairs or when additional cables need to be installed along the same underground route.

In fact this is the very reason the underground electrical conduits and manholes are used: to facilitate maintenance, repair and upgrading of the underground electric cables in future, long after the building is completed and occupied.

At the base of the opening in Picture 5 is a layer of sand. It is a practice to put some river sand at the base and compact it to give about 4 inch thick after compaction.

Of course, before that sand is poured in, the ground at the bottom should be firm and solid. If the soil at the bottom of the pit has been spoilt because of water accumulating there, then pit bottom must be excavated further to remove the spoilt earth. This also means more sand may be needed as the volume to be refilled would then be larger.

There is one very important I would like readers to note, especially those directly involved in construction.

You must NEVER allow the contractor to just install the manhole without first being inspected by someone responsible.

If the preparation of the base of the pit is not good enough, the manhole may sink in sooner than you would hope for. To repair it would require re-excavation works which are usually messy.

Someone may need to take the blame. It is not always easy to cover up mistakes like these.

Picture 6 – Excavated pit for an electrical manhole

I just include this picture to make my point above.

This particular opening in the ground was made in front of an electrical substation. It was supposed to be for the manhole of the same type and size as shown in the pictures above.

However, for some reasons the delivery of the factory-manufactured manhole did not arrive. So the opening was just left there. Sooner or later it would collect rainwater, which it did as can be seen in the picture.

Suppose one day the contractor calls you and say that he has finished installing the underground electrical manhole in front of the substation. With that the electrical authority can start pulling in the high voltage electrical cables.

In two weeks, the substation would be energized and the new building would have permanent electrical power that would also facilitate the testing and commissioning of all the electrical and mechanical services in the building, which has been delayed due to the delayed energization of the electrical substation.

This was a good news, and a reason for celebration. Of course, the real celebration should be AFTER the actual energization of the substation.

Being the one giving the good news to you, the contractor has made a dinner reservation at a nearby six-star hotel. It is a celebration and YOU are the man.

What would you do?

What would I do? I would accept the invitation to the dinner. After having a very nice meal and laughs, I would excuse myself earlier than normal. On the way out, I would tell the contractor to immediately start the arrangement to remove the installed manhole and prepare again the manhole pit in front of the substation.

Only after I say okay he would be allowed to re-install the manhole.

What would you do?

Copyright Underground electrical manhole

Thursday, July 29, 2010

Compound lighting foundation size

I am sending up the following three images on compound lighting pole foundation details to fulfill a request by a friend earlier today.

Image 1 – The overall diagram of a five-meter lighting pole

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About the author:

He was supervising a construction job of several pumping stations at a remote location in the countryside.

The project was worth just above ten million (I think that was what he told me a few months ago), so the budget for the supervision team was not that high.

Being a little bit out of the way, not many engineers would be interested to fulfill the vacancies for the resident engineer posts with the salary the engineering consultant could afford to pay.

However, the construction works still have to proceed and the project still need to be completed and delivered on time. No main contractor would want to risk any possibility of delays especially in a design-and-build or a turnkey contract.

As usual, the best solution in this sort of situations is to employ just one resident engineer to supervise both the electrical parts of the work.

This way the salaries meant for two resident engineers (i.e. for electrical and mechanical resident engineers) is paid to just one making the vacant post much more attractive.

That was the kind of post this friend of mine took and he got a pretty good offer to supervise a relatively small jab.

Naturally there is a problem, however. He is a mechanical engineer who needs to look after all the electrical works also.

He needs a friend’s help now and then to ask for some free professional advice.

That was what happened today. He needed to advise the electrical contractor on the size of the foundation for the compound lighting pole.

Image 2 – The blow-up view of the foundation for the 5 meter compound light pole

There not much that I need to elaborate on this concrete foundation. It’s just a simple plinth with the size of 500mm x 500mm x 900mm.

Notice the mounting bolts and the high impact PVC pipe cast into the concrete.

This image above shows just one uPVC pipe sleeve. Normally you would want at least two sleeves: one to the left and one to the right because cables to the light poles are usually looped in and out from the previous pole and then to the next pole.

So the image above if for a pole that is on the end of the loop.

Observe also that the dimensions of the concrete base are sized at bit larger than the base plate or the bearing plate of the steel pole (See Image 3 below).

Image 3 – Bearing plate dimensions

This is to give enough clearance around all the mounting bolts so that there is enough strength of the concrete to withstand the load imposed to each of the bolt.

The size of the foundation above is actually one of the standard practices that I know for the light pole height shown above and you should have nothing to worry about.

Of course the type of the soil is a major factor. So if you have doubts just call the light pole supplier or just ask the civil engineer. This is just a simple common issue for them, so you should be able to get an immediate confirmation.

I have been using this size in all my projects and never had any problem.

See you again the next time.

Copyright Compound lighting foundation size

Friday, July 23, 2010

Site fabricated electrical trunking

What will be the problem if an electrical contractor fabricates the electrical trunking at the construction site? Why do I make an issue of this matter?

Picture 1 – Electrical trunking already installed at a new building under construction

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About the author:

Majority of Clients and Consultants that I know specifically state that all electrical trunking and the related accessories should be factory-manufactured and should preferably be obtained from the same manufacturer.

This means that all parts and pieces that make up an electrical trunking installation should purchased as finished products from factory.

Observe from Picture 1 above that one of the electrical trunking has been bent. That was to make room for something else that would be installed there later (it was not yet installed at the time this picture was taken. I am not yet very sure myself what that something is… which reminds me that I need to check it out soon).

The point here is that now and then electrical trunking need to bend and turn around things and other services and equipment along their path inside a building.

Because of that, we need the angle pieces of the trunking.

However, fabricating an angle piece from a straight trunking piece is the most economical alternative for many electrical subcontractors. That is why many of them usually try very hard to use this alternative rather than buying them ready-made from factory as specifically required by the Contract Specifications.

I was once faced with a contractor who just bulldozed their way and installed the site-fabricated trunking bends for eleven of the twenty floors of an office building.

The contractor thought he could play hardball and force me to accept and approve the installation.

Too bad he lost the battle in the end and he had to spend all the manpower and the extra “factory-manufactured” materials to redo the trunking installation.

The worst thing was that all the wiring had already been installed.

The three pictures below show a trunking bend being fabricated by the electrical worker at a construction site that I was involved in.

I rejected these works also and the rectification work should be done by the electrical subcontractor. The contractor knew I would not accept this sort of quality, but he thought he was smart I guess.

Why such a big fuss over this matter?

Because the site fabricated trunking accessories are almost always of very poor quality. The finished product usually produces very sharp edges all over the piece.

The sharp edges cut into the insulation of the wiring cables during the cable installation. When the insulation is damaged all over the place along the length of a cable, then it is no longer a good cable no matter how much you paid for it.

Wiring cables that have been damaged in this way not only become a maintenance headache to the operation people after just a few years, they are also dangerous and can cause deadly electrical accidents.


Picture 2 – 45-degree trunking bend

Picture 3 – Sharp edges of the trunking bend

Picture 4 – Site workbench where the trunking “accessories” are “manufactured”

That is all the time I have for this blog today. Visit this post, Electrical installation pictures, to see more pictures of electrical installations.

There are other posts that I have sent a few months back about electrical trunking installation. You need to browse around this blog see them. I will put their direct links to this post in a few days for the readers’ convenience.

One last note: I wish to apologize to my regular visitors for being away this past few weeks. I know this blog has been getting regular visits from quite a number of readers.

The last few projects that I have been involved in have been taking too much of my time and energy, too much more than I would normally like to spend.

I also wish to thank the readers who have left messages. If you like these pictures, visit again.

I, however, will not be answering messages yet on this blog because I think this blog has not yet enough contents.

Not only that, once I start answering your messages, then I would feel very guilty when I cannot spare time on them.

Again thank you for visiting. I sincerely hope that pictures and other information that I put up here are useful to you all.

See you again soon.

Copyright Site-fabricated electrical trunking

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

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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

Wednesday, April 28, 2010

Electrical socket extension unit

Have you ever wondered how it looks inside the extension unit of electrical power socket? The following few pictures can help you appreciate what is going on inside this piece of common household items.

Picture 1 – The inside view of the electrical socket extension unit

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About the author:

I think most readers can understand this picture clearly with the labels that I added.

For the absolute beginners that need explanations on what does what in this picture, let me just give brief descriptions.

Extension cord

I guess everyone knows this part. The extension cable has a three-pin plug at the other end of it. It is the plug that you insert into the wall socket.

Look at Picture 7 below to see the complete set of the extension socket and plug.

Extension cables

The extension cable that you see actually has three insulated cables inside it: the LIVE cable, the NEUTRAL cable and the EARTH cable.

Each of the three cables has their own color-coded insulation: Brown for LIVE; Blue for NEUTRAL and Green with yellow stripes for EARTH.

When you work on the connections of these cables, you have to make sure not to connect them in a wrong way.

If you connect in a wrong way, the electrical appliance that takes power from this extension sockets may still work.

For example, you mistakenly swap the connections of the blue and the brown cables.

However, the ON/OFF switch (the red colored piece in Picture 1) is located at the LIVE connection. Therefore, there is still a voltage going to the appliance connected to the socket.

Cable termination screws

There are 3 cables coming from the extension cord. So you have three connection points and therefore 3 connection screws.

The connection screw may seem simple enough, but not using it properly has been the cause of many house fires all over the world. See Picture 2 below for a closer view.

Picture 2 – Cable termination screws

This is one of the biggest problems with house electrical wiring: the electrical parts look simple enough that everybody thinks they can handle it.

Yes, it is easy. But you must know enough about how the electrical components works to be able to handle it SAFELY.

If you do your own wiring, and you happen to replace an extension cord like one in the picture, make sure the connection of the copper conductor to the termination screw is strong and tight.

If the connection is not tight, then connection surfaces between the copper conductor and the screw present a high resistance to the current flow when the electrical appliance is turned on.

This high resistance will cause a high-energy loss at the connection, which is dissipated in the form of heat.

Over time, if the appliance is in operation long enough, the extension socket unit may overheat and become a source of fire.

A combustible material nearby such as a window curtain, old newspapers, even carpets and rugs may catch fire.

That is how a house electrical fire can get started. It is one of the most common cause also.

LIVE and NEUTRAL busbars

Picture 3 below gives a better view of the three busbars.

Picture 3 – Busbar connections

As the cables are connected to the termination screws from the right side, the busbars are connected from the right side.

I know there are readers who are not very familiar with the word “busbar”. So let me just spend a few words on this part.

The purpose of a busbar is similar to electrical cables, which is to carry electric current.

In cables, we normally put insulation over the current carrying conductor. The reason to prevent touching of the conductor with other things and parts nearby.

However, at some places, there is already a very good place allocated to install the current carrying conductor. So the insulation may not be necessary.

The copper conductors inside the cables are flexible. This way it is easier to handle and bend around things.

However, making things flexible from metal materials cost money.

If at certain locations, the flexibility of the copper conductor is not necessary, then why waste money by using the flexible type, right?

Another advantage of using a solid conductor like busbar is that it is easier to make connection to it. In this case, multiple connections need to be made depending on how many socket points are needed.

I think the above description is enough to show what a busbar is.

It is “solid”, so it is a “bar”.

“Bus”? I am not that sure myself exactly why the this word is used here.

All the while, I only guessed that this word is used because in the old days, a “bus” is used to denote a main path, or a main road. That is where you could wait for a transport to go long distance.

You can also get the bus by waiting anywhere along the main road. My guess is that the public did not need to wait at the bus station or the “bus stop”.

That was the “bus transport”. This is the “bus bar”.

You can get power anywhere along the conductor part. There is no need to cut anything, or go to a terminal screw.

I am only guessing here. Your own guess is just as good as mine.

Now let’s go to the next component.

ON/OFF switch

Everybody knows what an ON/OFF switch is. It is exactly what the name says.

But there is one more component related to this on-off switch. It is called the pilot light.

Picture 4 – The pilot light

In picture above, the pilot light is labeled. When the on-off switch of a particular socket unit is switched on, this light turns on.

Trivial as it seems, this feature has a very important safety purpose on an electrical socket.

When the light is on, you know there is power going into your electrical appliance. Even when the appliance is not operating (maybe because the appliance built-in on-off swith has been turned off, or the equipment has a blown fuse), you know the power is there.

It is therefore still dangerous.

The pilot light helps train our habits about safety.

When it is ON, there is DANGER for sure. There is no way we can pretend the switch on the socket is OFF.

The pilot lamp is connected in parallel with the appliance (to be connected). So even when the appliance power cord is broken, the pilot lamp lights up when the socket switch is ON.

The earth connection piece

Please observe in Picture 4 above the connection pieces from all three busbars in side the pin sockets.

Notice that while inside the “LIVE pin socket” and the “NEUTRAL pin socket” the connection to the plugs pins are made using a separate piece, the connection piece inside the “EARTH pin socket” is NOT A SEPARATE PIECE.


Because it is EXTREMELY IMPORTANT that the grounding connection from the appliance to the electrical grounding system MUST NEVER FAIL.

Therefore, the connection piece for the earth pin is part of the earth busbar.

Both is made from one solid piece of conductor and then bent around to form the earth busbar and the earth contacts (three sets of earth contacts actually, because there are three socket outlets in this socket extension unit).

Picture 5 below shows how the plug pins are inserted into the sockets.

Picture 5 – 13A sockets and a plug

Picture 6 and 7 below just show the whole assembly for readers who need them.

Picture 6 – The cover for the cable termination compartment removed

Picture 7 – The whole 13A socket extension assembly

I will see you again in the next post.

Copyright Electrical socket extension unit

Monday, April 26, 2010

Feeder pillar hazard pictures

I think anybody with even a minimal amount of knowledge on the hazards presented by electrical equipment installed in public places know what is wrong with the feeder pillars in the picture below.

Picture 1 – Wrongly designed feeder pillar??

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About the author:

I always avoid criticizing other people’s electrical designs based on evidence that is seen after installation has been completed because the outcome of a completed electrical installation is the products of many variables and factors.

Especially with the popularity of design-and-build and turnkeys types of contracts.

In these types of contracts, the main contractor is the boss and the employer of the professional consultants.

How professional can a consultant-engineer be when his paymaster is the main contractor?

Now let us get back to the picture above.

I do not know if the above electrical feeder pillars were constructed in a turnkey contract or not. I only passed by the area to find a place to eat.

However, the sight of these lovely feeder pillars caught my attention while I was looking for a parking space.

What is wrong with these feeder pillars?

I am not talking about age of the feeder pillars.

I know that everything gets old some day. Machines get worn out, the materials get deteriorated and the lovely paintwork fades out.

They do get old, just like us.

However, machines and equipment that can endanger people especially children should be designed and installed with safety as the most important criteria.

The feeder pillars above have failed in that respect. Look at Picture 2 below.

Picture 2 – Inadequate protection against electric shocks

Here you can see a hole at the feeder pillar front door.

The brownish rectangular material at the feeder pillar front door can only mean one thing: there is a kilowatt-hour (KWh) meter inside it.

The brownish material used to be a transparent material so someone could read the reading of the energy meter.

It is a usual practice to install a separate meter for the lighting of public spaces at a private compound because the owner or the property management could apply for a lower tariff on the electricity used by the carpark lights or road lights.

The feeder pillar that supplies the public lighting is where the authority KWh meter is installed.

At many installations, the design of these feeder pillars as shown in the above pictures should be adequate. It is actually one of the standard designs and therefore this design is widely used.

However, these particular feeder pillars were installed at open public spaces with open to public carpark and a number of recreational spots nearby.

In other words, now and then this place is crowded with children.

The design of the feeder pillars as installed here in the picture is wrong and dangerous

How should it be designed?

I will post a diagram of how it should be in another post. Maybe a picture or two of actual installations if I can steal a few hours to go take the pictures.

For now let me just point out a few points:

1: the front doors of the feeder pillars should be done in two layers, both having sufficient weatherproofing qualities.

The inside door protects the components inside the feeder pillar. The kilowatt-hour meter can also be installed behind this inner door.

If that is the choice, then a waterproofed viewing glass window needs to be provided at the inner door, and it should be at close distance to the meter dial.

The second layer of the feeder pillar door is the outer door. This door also has a glass-viewing window (the second layer of glass windows) directly in front of the inner viewing window.

The primary purpose of the outer door is to serve as an outer barricade against access to live parts if the outer viewing glass gets broken for whatever reason. Because of that, it is preferable if sufficient gap is provided between the outer and the inner doors. This will result in a more effective barricade.

2: The viewing windows for the kilowatt-hour meters should be of the correct materials.

Every time I looked at the feeder pillars in the above pictures, I always wonder about the cause of the damaged viewing windows.

Was it vandalism?

Or maybe it was the employees of the electricity supply company who broke the viewing window? With the windows turning so brownish, how could the “meter readers” (this is what we call the public utility workers who come to read the electricity meters and issue the bills for the month) read the readings?

But then the viewing window of the second feeder pillar was not broken. Maybe the door of this one was not locked so there was no need to break it.

It does not matter who did it. When it comes to safety of the members of the public especially children, the design and installation people in electrical installation works should ensure that the completed works is adequately safe.

Why do I put so much emphasize on children?

Because they are curious little creatures.

When they see holes like one in Picture 2 above, someday one of them may be tempted to put his hand inside.

Enough said.

I will see you again in the next post.

Copyright Feeder pillar hazard pictures

Friday, April 16, 2010

Building’s electrical rooms layout

During the design of an electrical installation for a building, spaces that are required as electrical rooms need to be provided for very early in the planning and design process.

I will try to present this in a form of a few basic concepts so that non-electrical readers can benefit from it.

There are also a few diagrams at the end of this post, but I do want to go too technical here as this may turn off the non-electrical readers.

If you need a more technical discussion, I will send a few posts of electrical substation layout and design in future.

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About the author:

Sources of electrical supply

Two (or sometimes three) sources of electricity are normally required in high-rise buildings:

1) The normal mains supply from the electric supply authority or the local electricity supply company in some countries.

2) The standby or emergency supply for the standby electric generators. In most situations, this supply is not an option, but a mandatory requirement for buildings that exceed a certain size.

3) The uninterruptible power supplies, or commonly called UPS. This is only needed in certain types of office buildings and in some hospital buildings.

Voltage level of the incoming supply

The normal mains supply taken from the authority may be taken at HV (high voltage, normally 11 kV in this country), or LV (low voltage, 415 Volt, three-phase four-wire).

Whether it is the LV or HV supply depends on the size of the maximum electrical demand to be expected of the planned building when it is in full operation.

It also depends on the effects of voltage drops and the level of voltages that are currently available from the supply authority.

Authority’s HV room

When the incoming supply is HV, the authority usually only require a HV switch room to be built and handed over to them. This is where they house their high voltage switchgears and other equipment.

The location of the Authority’s HV room

The location of this room must allow for easy access by the authority’s maintenance people and it should not present an inconvenience to the occupants of the buildings or disrupts the building’s normal functions and operations.

(Separate meter room: At times, the local office of the electricity supply authority requires that a small meter room be provided and handed over to them. This is where they house the meter panel.)

Electrical distribution cables from the authority’s distribution network in the area will be tapped and looped to the HV switchgear panels in this room. They usually install a series of HV panels here.

Then from one of the HV panels, a supply feeder cable will be laid and connected to the consumer HV room.

Consumer HV room

A consumer HV room is generally a repeat of the authority’s HV room. The equipment and switchgears located in them are also similar.

The purpose of the consumer HV room is to house the equipment that are essential to the safe and proper handling of the electrical high voltage supply received from the authority’s HV room.

If the building management need to switch off the high voltage supply for some reasons, then this is where they do it.

Among the reasons may be if the transformer is faulty and need to be serviced ar checked.

Another reason may be if the transformer room is located at a separate location and the high voltage cables to the HV switchgear is by cables buried underground. Sometimes an excavation need to be carried out very close to the cable location that a complete shutdown to the supply carried by the cables is necessary.

The third scenario might be if the main low voltage switchboard (the electrical panels that receive the low voltage currents directly from the transformer) need maintenance or repair. Then the only way to make the main switchboard completely dead is by turning off the supply at the HV switchgears inside the consumer HV switchroom.

Can we turn off the supply by switching off the switchgears inside the authority’s HV room?

No, we can’t.

The room and all the equipment inside them are legally theirs now.

By transferring the HV electrical room to the authority, the building owner are actually required to sign some form of an agreement to transfer the ownership of the room to the electricity supply authority, or to lease it to them for a duration of 99 years I think.

It is like an embassy building in a foreign land.

Likewise, the supply authority is not allowed to freely access the consumer’s HV room or the equipment inside.

Metering CT

Buildings taking supply exceeding a certain amperes require the use of a set of CT’s (current transformers) in order to measure the energy consumption. The contractor of the new building will have to provide these CT’s.

However, the new CT’s also need to be sent for calibration and certification by the electric supply company before installation.

After the calibration, the CT’s are installed inside the consumer HV panels. A set of wiring are then installed to connect these measuring current transformers to the authority meter panel inside the meter room.

Authority’s transformer room

Sometimes during the negotiations on the application of the supply, the authority may require that a transformer room is also provided and handed over to them together with the HV room.

Usually this happens when there is no suitable site available for their substation in the vicinity of the area, such as when the planned building site is at a congested area of towns like the city center.

When transformer room(s) is required, the authority electrical substation would be a complete substation, not just a HV room.

This means that the substation may also be used to supply other buildings and properties nearby.

Distance from Authority HV room to Consumer HV room

As mentioned, the HV feeder cables that will carry the electric current to the planned building will need to connect to the consumer’s HV switchboard in the consumer HV room.

Part of the cost born by the authority in order to give supply to the new building are usually charged to the consumer (in what is usually called a “contribution fee”) and need to be paid before the authority commence their installation work.

Therefore, the nearer the consumer HV room is to the authority HV room, the shorter the HV cables that need to be laid and the lower the cost of the cables that need to be shared by both parties.

So in many cases, the consumer HV room needs to be nearer to the authority’s HV room.

In construction projects where the land space is limited such as building projects, it is highly recommended to locate the HV electrical rooms as close to each others for another reason.

Areas where high voltage equipment and cabling are installed need to be controlled as a restricted area. Locating the HV room near each other would make control easier and the restricted area would take less space.

Consumer’s transformer room, LV room, standby generator room and UPS room

Other than the HV room, the consumer also needs a transformer room, the LV room and the standby generator room. When a large UPS supply is used, then a UPS room may also be needed.

LV room and transformer room to be as close as possible

The consumer transformer room and the LV room need to be as close to each other as possible in order to minimize the voltage drop.

For every meter of extra distance between these two rooms, a significant cost needs to be spent to overcome the voltage drop to an acceptable level.

The cables used to carry the low voltage electrical supply also are usually of very large diameters.

Large diameter electrical cables are very difficult to maneuver and bend around corners and tight areas.

Keeping the two electrical rooms close to each other effectively reduces the bends needed of the electrical cables.

Supply intake at LV

If the electricity supply taken from the authority is LV (low voltage), then they will require a HV room and a transformer room to be provided. The two rooms must be situated adjacent to each other although sometimes they accept that the HV switchgear and the electrical transformers share the same room to save space.

The consumer is also required to provide a main switchroom adjacent to the transformer room. The standby generator room also needs to be near the main switchroom.

However, if the electrical energy required by the building is less that about 300 KVA, no electrical room is required to be prepared and handed over to the electrical authority.

They will tap off the supply from a nearby existing electrical substation or tap it off from an existing low voltage distribution network.

It is for this reason that some property developers submit their application of electric supply in stages with each stage requiring not more than 300kVA.

All the above electrical rooms are needed so we can receive supply from the public mains.

However, there is the second type of electrical supply in a building operation, which is the standby generator supply. I will not talk about the third type, the UPS supply (uninterruptible power supply) today because only certain types of buildings use it. I will address that topic in a separate post.

Standby diesel generator room

As I said earlier, no building exceeding a certain size or a certain height is allowed to be operated or occupied without some form of a standby emergency power.

The “emergency” here means when the public electrical supply is suddenly not available.

It also means a fire situation because a normal electric cable would fail under fire and the fire fighting equipment would need “emergency” power so the firemen could use them.

Now, this standby diesel generator and all its ancillary equipment need a room to house them in.

However, the electric generator is a bulky and noisy machine. It also produces very strong vibrations that can be transferred to the building walls and structure.

Therefore, a room for this electrical generator need to be specially designed and the room location need to be purposely located.

If you are given the freedom to make a decision, make a small separate building to house this noisy electrical generator, preferable somewhere hidden behind the main building.

Then build up all other main electrical rooms that I described earlier around the generator room.

If you start that way, you will have no problem later when the issues of noise level, engine exhaust, radiator exhaust, fresh air intake, maintenance access route and fuel storage tank come into play.

That is usually the time when the architect and the building owner start asking whether we can exhaust the radiator hot air at the third floor level 50 meters away.

Locations of substation rooms

The actual locations of the electrical rooms at the building complex are a major factor in the design of all types of electrical installations. There are a few major requirements that must be taken into account when deciding on the locations for these rooms.

1) They should be located inside the buildings, as near as possible to the load centers.

2) The electrical rooms should be as near as possible to each other.

3) The rooms need to be accessible by maintenance vehicles and maintenance people for purposes of installation, operation and maintenance works. This should be possible without disrupting the normal operation of the building.

4) They should be accessible by heavy vehicles during installation and when replacement of heavy equipment is necessary.

5) They should be adequately ventilated.

6) All electrical rooms should be adequately secured from possible disasters like flood, or even vandalism.

The above electrical rooms are in the category of substation rooms. For aesthetic reasons, layout of the buildings can be made such that the electrical rooms are located at a separate building adjacent or hidden behind the main buildings.

In fact, it is even preferable for the rooms to be secluded somewhere as long as all the above criteria are met because that would reduce the risks of interference to the functioning of the electrical system including accidents and even vandalism.

However, there are still a few more electrical rooms, which are needed for proper and efficient operation of an electrical installation in all buildings especially those of the multi storey and high rise types.

Other electrical rooms:

1) Electrical service ducts

Electrical service ducts or electrical riser rooms are used to house the submain cables that carry electricity supply to the upper floors of a building, which include the plants and machines at the roof top such as the chiller plants, cooling towers or the lift motor rooms.

The rising mains that supply the lateral distributions on individual floors are also located in these vertical ducts.

Often these concrete vertical ducts are as large as a small room. That is why it is often called electrical riser rooms.

The electrical riser rooms do not have to be stacked vertically like the toilet risers or wet stacks.

However, it is better to do so as it would minimize turns and sharp bends that can damage the cables.

Riser rooms stacked straight up from the lowest floor to the highest building floor would also minimize the length of the electrical cables required.

Minimum cable length not only reduces the cost directly. Longer route of an electrical cable run may cause too much voltage drop along its length that may require it to be changed to one or two size larger.

Larger cables cost more money.

2) Individual floor electrical rooms

Each individual floors of significant size will usually need at least one dedicated electrical room to house the electrical distribution equipment for that floor.

However, sometimes the vertical service ducts may be able to fulfill this function in which case a separate electrical room may not be necessary.

The architect may then need to make these service ducts bigger to give them enough space for proper operation and maintenance.

The electrical rooms at each floor house the electrical panels that serve the final circuit wiring.

Therefore, they should be as close as possible to the load center of the area that it serves.

Very tall buildings

If the planned building is very high (let’s say a 40 storey office building), or in cases where heavy loads are located at higher levels of the building, it may be necessary to provide substations at the higher levels of the building.

For the 40-storey office building, an 11/.415 kV substation may be necessary at one of the upper floor. It may be located at twentieth floor, for example.

All the electrical substation room spaces as explained earlier will then need to be provided except the authority’s electrical rooms.

The floors of this substation would then need to be specifically designed by the appointed structural consultants to handle the loads of all the substation equipment.

Electrical rooms must be planned for early in the design stage

The above requirements need to be planned for at the early stages of the design and coordinated with the architects and structural engineers.

In many projects, the room spaces and their locations as requested by the electrical engineers are subject to “negotiations” with the architects and structural engineers, not merely technical coordination and interfacing.

But that can turn to be a controversial subject so I think having a separate post on it will be better.

That is all I want to say on the electrical rooms today. I will continue again in the next post.

However, there are a few diagrams of electrical room layout that I think can help some readers make more sense of what I described above.

Diagrams of electrical rooms:

The first few diagrams show the core layout of a nurses' apartment building. The core layout means the layout of the building services infrastructure with the lift core at the center.

When the architect lays out the components of building services, this is what she need to place first.

Since this building is an eight storey building, I showed here the layouts of a few floors. This will help you see how the electrical rooms and the rooms of a few other building services go up the building floors.

I will not comment much on these diagrams today. Just observe the diagrams and you will be able to see the logic behind them.

Diagram 1 – Ground floor layout of building services

I will explain a little bit here to help the freshies get started.

ELEC – electrical riser room (I have uploaded some pictures of electrical riser rooms at this post: Electrical busduct installation pictures. Click the link and you can see what electrical rooms look like in an actual installation).

MATV - the riser room for the MATV (master antenna television) system. If the building has a CCTV (closed circuit television) system, the riser cables will run inside this riser shaft to connect to upper floors of the building.

In many building design, a single riser shaft is used to run all the ELV (extra low voltage) services to the upper floors.

(Note: When all the riser rooms at each floor are stacked up vertically straight up, then it forms a shaft. So it is called a riser shaft.

Put in another way, a long time ago when the ancient builders found out how to build a building with multiple floors one on top of the other, the riser started as shaft or a vertical wooden duct.

In order to make it safe for working inside it at each floor, they extended the floor into part of the riser. Then it became like a room. So it was called a riser room.)

TEL – for telephone cables and equipment.

DR – dry riser. A building exceeding a certain height is required to install vertical pipes with inlets at the ground level. These pipes will be used to pump water from fire engines to the upper floors so the firefighters can fight fire.

If the building height is even higher, dry pipe riser would not be accepted by the fire department. A wet riser system would then be required. This is the same piping as the dry riser but with water tanks to store water and sufficient number and horsepower of pumps to always keep the water under sufficient pressure in case there is a fire in the building.

WATER – Water is not available here. Just pipes that carries domestic water. Designers just label it WATER as a short form for COLD WATER.

ON CALL – You would only have this at residential buildings for hospital employees. They have a communication system that can call the employees on standby when they have to report for duty immediately.

The red rectangular symbol inside the electrical riser is the electrical panel. You will find one or more electrical panels at the upper floors also.

Diagram 2 – First floor layout

Diagram 3 – Sixth floor layout

Diagram 4 – Layout for seventh and eighth floor

The eighth floor is the highest occupied floor inside this building. The floor above is just a roof level that is normally used to locate some mechanical services and fire fighting equipment and plants.

If there is a centralized air conditioning system in this building, then the cooling tower may also be located here.

Diagram 5 – Closer view of the electrical riser room and the Main DB

I zoom specifically to this area to show you what is supposed to be inside the electrical riser room.

Observe the legend for the upper electrical panel symbol.

The symbol legend MDB ‘7F’ stands for Main Distribution Board No 7F. “7F” means Seventh Floor.

The lower electrical panel symbol represents two electrical panels, each with labels DB ‘CR-7’ and DB ‘ECR-3’.

So there are three electrical panels inside this riser room.

I will explain why one of the DB’s is called Main DB when I touched a little on the single line diagram of the MDB in Diagram 7 below.

Diagram 6 – Layout for roof level

Diagram 7 – The single line diagram for individual apartment’s electrical panel

The main electrical supply cables to the upper floors are run inside the riser shaft.

The electrical panel for each individual nurses’ apartment is inside the apartment unit itself.

Diagram 7 above shows a typical single line diagram of the wiring for each apartment.

Now in order to get the electrical power, each of these electrical panels needs to be connected to the riser cables.

There are eight apartment units at each floor. So there would be eight sets of tap off unit attached to the riser cable inside the electrical riser shaft.

This quantity of tap off units can present many maintenance problems during operation of the building.

Moreover, the cables connected to the tap off unit also need to be protected with a circuit breaker. That means we need a panel to house the circuit breakers.

With eight units of apartment needing supply, we might as well install a large electrical panel to house all the circuit breakers to protect all the supply cables to the eight apartments.

Then we can use a busbar to supply all the eight circuit breakers.

This way only one set of tap off unit is required, which is to supply the distribution busbar inside the panel.

This is what is represented by the schematic single line diagram in Diagram 9 below.

Diagram 8 – Single line diagram of Main DB

With the entire individual apartment DB’s taking supply from this electrical panel, it is called Main DB or MDB.

Don’t let all these names confuse you. Some would call this Main DB a sub-switchboard, or a floor DB.

It is just an electrical panel upstream of the other in the hierarchy of the electric power distribution system of the building.

Okay guys. I would love to continue this further as I have not yet touch on the diagrams of the substation rooms.

It’s already 3.30 in the morning. So I will continue with this in the next post, okay.

Copyright Building’s electrical rooms layout