Electrical busduct installation pictures

The following pictures show electrical busduct risers in actual installation.

Picture 1 – Typical busduct rising main at individual building floors



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The above picture shows a typical installation of busduct rising mains in the riser room at individual floor of a high rise building.

This picture was taken in the riser room at one of the upper floors of a high rise building.

From the picture you can see most of the major components of a busduct riser system.

(NOTE: for readers who are not from electrical disciplines, a “riser” is a feeding cable or pipe giving supply to upper floors of a multi-storey building.

In electrical works, a riser is a set of cables the supply the upper floors. The electrical distribution diagram in Diagram 3 may make you understand this better.

The feeding cables “rise” up straight to the top floor. Then at each floor a tap-off unit is connected so electricity can be supplied to that floor.

An alternative is to run one individual set of cables to each floor. Then there would be many cables that need to be installed the number of which is directly proportional to the number of upper floors.

One single set of bigger cables is always cheaper to install and much easier to handle.)

Observe that there are three tap off units there: two units of 60A three phase, and one unit of 100A three phase. The one at the highest position of the three is the 100A tap off.

Why three units?

There are actually three risers here: one for the “normal” main electricity supply. This supply is just the normal authority supply like the one you have in your house. The 100A tap off unit is for this riser.

The second tap off, which is one of the 60A units, is what is called “essential supply”, or “emergency supply”. It is a normal authority supply like the one you have from the 100A tap off unit above.

However, it is also backed by a standby diesel generator. This means that if the electricity supply from the authority distribution network fails due to problem with their underground distribution cables or whatever, the standby electric generator would kick in and switch in the locally generated electricity to this electrical riser.

Large capacity electric generators are expensive, however.

Therefore, it is not economical to supply all electricity needs in the building from this generator. That is why separate electrical risers are used, and the “normal” riser is not backed by the generator supply.

The third tap off unit (the second 60A unit) is for the air conditioning system.

It is quite common (and is considered a better design) to have a separate feeder cable for the air conditioning and mechanical ventilation (ACMV) system in a large building. That is the reason for the third electrical riser here.

One more point to note here is that some office buildings use the generator-backed supply (i.e. ESSENTIAL supply) to feed the electrical riser for the air-conditioning system.

With this arrangement, ACMV equipment that need to continue operating even during the mains failure do not need to be connected to “ESSENTIAL” supply riser, which is why it is given a separate riser in the first place.

Observe the large flexible conduits coming out from the bottom of the tap off units and connect to the orange-colored electrical trunking. Some installations use rigid metal trunking for this purpose.

Cables are run from a tap off unit into the flexible conduit to go to the orange metal trunking.

They run inside the trunking to connect to the respective sub-switchboard.

You can see only two sub-switchboards here. These are for the “NORMAL” supply and the “ESSENTIAL” supply.

The switchboard for the air conditioning system is normally located inside the AHU room of that particular floor.

From the sub-switchboards, separate outgoing cables are run inside the trunking to connect to separate distribution boards (DB) on that particular floor.

That is all that I wish to elaborate on Picture 1 above.

My intention is so that beginners in electrical installations can understand the major components that make up a busduct riser system.

Now let us look at a few electrical diagrams. The diagrams can give a more complete overall view of a simple electrical system in which a similar busduct riser forms a part.

While the busduct risers in Picture 1 are for a high rise office building, the following diagrams are for much simpler installations. They are for the nurses hostels at a hospital complex.

Even though electrical installations at hospitals are relatively much more complex than the office building above, the installation at their hostel and staff quarters buildings are usually very simple.

That is why I choose to use them here. My objective here is to give casual readers and beginners in electrical works an overview and general understanding of the basic functions and installation of a busduct riser system.

The actual electrical diagram used to construct the installation in Picture 1 might be too complicated for this category of readers. I do not wish to scare them away.

Diagram 2 – Part single line diagram for a multi-storey nurses hostel



This diagram is part of a larger diagram which is in Diagram 3.

Diagram 3 – The full layout of the single-line of Diagram 2



As you can see, you cannot read much of the labels and notes in Diagram 3.

I produced this JPEG graphic from an AutoCAD drawing files (i.e. DWG file format) which is probably the most widely used drawing programs in the construction industry.

I used the program’s BMPOUT command to produce a BMP file format form the DWG file format. Then I converted the BMP format into the JPEG file format using the Microsoft Paint program.

However, this method does not seem to be effective enough for AutoCAD drawings that have been produced for A1 or A0 printing as the original sizes.

If anybody here knows a better method, please let me know.

Okay. Let’s get back to the electrical single-line diagrams.

In Diagram 1, you can see that the hostel building is six-storey, which Ground Floor, then Level 1 to Level 5.

Usually for a building of this height, designers do not use busducts. However, they do in this case. Maybe that was because the project already used so many busducts at the main hospital complex and other (much higher) staff quarters buildings, it made sense to also use busducts here.

In any case, the components of the busduct system that you see in Picture 1 were used at each floor of Level 1 to Level 5.

However, at Level 1 you have one or two more components. Picture 4 below shows a view of the electrical riser room at Level 1 (the first higher level). It is the same building as that in Picture 1.

Picture 4 – A view of the electrical riser room at Level 1 (the first level above ground level



As you can see, there are definitely more components here that in Picture 1.

However, actually there are basically only two new components at each riser, which is the TERMINATION BOX (some people call it “FEED IN BOX”), and the incoming cables that terminate into the termination box.

Apparently there is an extra tap off unit here, but it is the same component type.

Observe the cables coming into the termination boxes.

The biggest termination box has cables with black insulation terminated to it, while the other two termination box has red cables.

The red cables are red-colored because they are fire rated cables. Remember the “NORMAL” and “ESSENTIAL” supplies that I explained above.

Why the generator-backed “ESSENTIAL” supply cables need to have red colored insulation?

It is because this supply is part of the fire emergency system of the building. Which means this part of the electrical installation system must also comply with the Fire Requirements of the Building Bylaws and the Fire Department.

A fire-rated cable must be able to continue operating for a certain number of hours during fire before it fails. This is the requirement. It used to be MICC (mineral insulated copper cables) cables that play this role, but now people use mostly the “fire-rated cables” for this purpose except in very special installation condition.

The fire-rated cables are cheaper, easy to install and maintain.

(See more pictures of fire-rated FR cables at this post, FR electric cable installation pictures.)

The black-colored cables are from the “NORMAL” supply. That means the other ends of the cables are connected to the “NORMAL SUPPLY” main switchboard.

While the red cables are connected to the “ESSENTIAL SUPPLY” main switchboard.

Which means the “ESSENTIAL SUPPLY” main switchboard is the one that is backed by the standby electric generator.

Is it too complicated? I hope not.

Even if it is, have no worry. I will spend a post or two on the overall system of electrical installation for large multi-storey buildings soon. Now I am actually building up section by section.

I will end this post by attaching a single-line diagram for a building similar to that of Diagram 4. However, this one used the normal cable riser instead of busduct riser. I hope the all readers of this post can locate the difference in the two diagrams.

There are also a few more pictures for the risers of Picture 1 and Picture 4. These pictures provide more information and better views for a few of the busduct components.

Diagram 5 – A distribution system using a cable riser instead of the busduct riser



Picture 6 – Another view of the busduct risers at riser room



Picture 7 – The front view of one of the 60A TPN tap off units



Picture 8 – A closer view of the vertical busduct showing the arrangement of the conductors inside



Notice that there are five conductors inside the busducts: the three phases, the NEUTRAL conductor and the EARTH conductor. The arrangements of the conductors are as shown on the busduct casing.

Picture 9 – A view of the cable entry into the feed in box and the connection of the equi-potential earth conductor



Observe that the copper tape was connected to a wrong place.

The metal plate where the cables are connected to is a removable plate. The copper earth tape should stay clear of this removable plate.

The tape should be connected to the main body of the termination box at a location where it is least likely to be disturbed.

This installation work was actually still in progress when I took these pictures. The copper tape connection was later rectified.

You can see more pictures at this post, Electrical installation pictures.
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Switchboard earthing pictures

This post provides a few pictures of switchboard earthing. They are pictures of actual switchboards and electrical DB’s that were installed in one of the projects I was involved in.

Picture 1 – LV sub-switchboard



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Picture 2 – Three-pole 160 A Terasaki MCCB and the neutral link



Picture 1 above shows a sub-switchboard at one of the upper floor of the multi-storey building.

Picture 2 shows the main isolation switch at the switchboard. I show the enlarged version of this component because I want to show the readers the neutral link component on the right of the MCCB. The neutral link is a very important part of the safety aspects of an electrical installation. I may want to refer to component later in this post or maybe when I send an update.

In Picture 1, you can see at the bottom left corner of the sub-switchboard the earthing connection to earth the switchboard front door. Picture 3 below gives an enlarged view.

Picture 3 – Earthing conductor to earth the sub-switchboard front door




Observe that the conductor is made of braided aluminium conductor. The braided type of conductor is a very good material for earthing door switchboards because the door is a frequently moved part of the board.

If an unsuitable material is used, the frequent movement of the door will either weaken and damage the conductor, or loosen the contacts at the door and the main panel cubicle. A loosened contact would increase the contact electrical resistance and defeats the purpose of having a properly sized earth conductor in the first place.

A loosened earth conductor is usually seldom noticed during the operation of the equipment until something happens. The problem is that “something” may actually be a serious electrical shock.

It is for this reason the earthing of these grounding connections should be properly checked by visual inspection during the installation works.

Notice also the termination to the switchboard door. The braided aluminium conductor is terminated using a compression type cable termination lug. It is fixed to the door using appropriately sized earthing bolt and nut with spring washers.

Picture 4 – Lighting and small power distribution board (DB)




Picture 4 above shows a floor distribution board for the lighting final circuits and also for the small power needs at the floor level.

Both the sub-switchboard in Picture 1 and this DB were not actually installed yet at the time I took these pictures. They were still on the floor at the storage area of the construction site. That is why you see these pictures were taken at angles looking downward to the boards.

The earthing connection to the front door of the board was also using the braided aluminium similar to Picture 1, as shown in the enlarged view below.

Picture 5 – DB door earthing conductor



There also is another type of panel door earthing conductor in common practice, as you can see in Picture 6 and Picture 7 below.

Picture 6 – Another electrical DB




Picture 7 – DB door earthing using green insulated PVC cable



Here the conductor is just the normal PVC insulated wiring cable with green colored insulation. The PVC cable is not very flexible. It is therefore is installed in the inverted U-shape as in Picture 7.

Sometimes the PVC cable is formed into coils between the two mounting bolts to give similar flexibility. I do not have the picture of this method now, but I will send an update as soon as I can get one.

I personally prefer the braided aluminium conductor as in Picture 1. However, contractors would normally prefer the PVC cable type because it is simply cheaper.

Manufactures would always prefer the Picture 1 method because it make the their board looks more high-quality. However, they would have to follow contractor’s choice unless the design consultant specifically stated their requirements clearly in the contract specifications.

Main Earthing Cable

In all the above Pictures, I have only highlighted the internal branch earth connections. I wish to highlight the main earthing conductors of the switchboards.

Look at the bottom of the distribution board in Picture 6. You can see at the bottom of the DB cubicle a length of green PVC insulated wire just laid there and stops just below the three-pole MCB at the bottom right corner of the DB. You can see it better in the enlarged view (Picture 8) below.

Picture 8 – Distribution board main cables



Unlike the first two electrical panels, this distribution board has already been wall-mounted in its final position. However, it is not yet wired and the cables not terminated. The electrical contractor just wanted to get my approval of the DB mounting method before they proceed with the cable termination works.

You can see the sub-main supply cables coming down from the top trunking. The outer sheath and wire armor of the 4-core armored PVC cables have been terminated with a cable gland. That is why you can see the individual cable cores coming down along the right side of the cubicle wall.

An extra slack has been provided during the sub-main cable installation to ensure there is enough length provided in case adjustment need to be made to the final position of the DB. The actual route inside the DB also may require some extra slack to the incoming cable cores.

Back to the earthing cable. The specifications for this project requires the use of 3 mm by 75 mm copper tapes as the earthing conductors for all submain circuit.

However due to installation difficulties I have allowed the use of PVC copper cables as an alternative to earth the sub-switchboards and distribution boards on case by case basis. This DB is one of the cases.

Therefore, here the main earth conductor is the PVC cable. This cable is connected to the main earthing conductor, which is the 3 mm x 75 mm copper tape, at the multi-storey building’s riser room.

You can see in Picture 8 that the earthing cable is not terminated yet. It is a common practice to provide a main earthing busbar in side an electrical board. The earthing busbar is usually pre-installed at the factory just like the rest of the components.

I do not see the earth busbar in the picture. When I went for the inspection and took these pictures, I was only paying attention to the mounting of the board. I only realized the missing earth busbar when I started to write this article. In any case, this matter would be picked up during the inspection of the internal wiring of the distribution board.

If the main earth busbar is actually missing, the electrical contractor will need to install the busbar himself at a suitable location inside the DB. The green PVC cable will then be terminated to the busbar using compression type cable lug.

The fixing to the busbar will also be similar to the door earthing method explained above: bolt and nut with spring washer.

Usually the busbar would be pre-drilled with sufficient number of termination points plus a few spare points. This will eliminate the need for disassembly of the busbar and all existing connections when additional earthing connections are needed during the life of the switchboard.

There is one more picture that I would like you to see on the earthing of LV electrical panels. See Picture 9 below.

Picture 9 – Switchboard earthing conductor



Where is the switchboard??

They have not been installed yet at the time I took this picture. These “dropper trunkings” have been installed but they stop just a few feet above the location of the distribution board and switchboard.

Observe the two lengths 3 x 75mm copper tape coming down from the electro-galvanized steel trunking. This is the standard earthing conductor used for this project. The PVC cables used in Picture xx was a replacement to this copper tape.

Earthing of 11 kV switchboards

The switchboards and the distribution boards shown in all the above pictures are low voltage boards. They are rated 240V/415V at 50 Hz supply.

Now I will show you a few pictures of high voltage (HV) switchboards. These boards are designed for 11 kV incoming supply.

Picture 10 – 11 kV switchboard rear view



Picture 11 – Closer view of the earthing copper conductor



Why do I show the rear view of these HV panels?

Because these panels are floor mounted with rear access. The LV panels above have been designed for mall-mounted installation. Therefore, they do not have rear access.

Observe the long strip in brown color at the lower edge of the switchboard. This is the earthing copper conductor for the high voltage switchgear panels.

Note: Some readers may notice that I use the terms “board” and “panel” interchangeably. For LV small electrical panels the two terms do not really have any significant difference.

However, for large LV switchboards and high voltage switchboards, the two terms cannot be interchangeable. Look at Picture 12 below.

Picture 12 – HV panel



This is one HV panel. The other big object at the left of the panels is actually another HV panel, which is still inside its waterproofed wrapping.

A high voltage switchboard consists of one or more of these panels. In other words, the panel is a section of the switchboard.

Notice the brown strip at the bottom edge of the panel in Picture 11. This is the earthing copper conductor that you see in Picture 10.

From this picture it is obvious that the long copper strip in Picture 10 is actually jointed lengths of short individual copper strip that are part of the individual HV panels.

This short copper strip at each panel has actually been installed at the manufacturer’s factory. Short lengths of the conductors are then provided complete with pre-made jointing holes and shipped together with the rest of the panels.

The electrical contractor then only needs to re-assemble all the pieces together into a complete HV switchboard.

Picture 13 – Another view of the earthing conductor




This photograph also shows the HV cables installed in the cable trench. The one going into the end panel is the feeder cable to one of the local transformers. While the other one is the incoming supply cable from the authority HV switchroom just adjacent to this HV switchroom.

Picture 14 – Substation earthing



Picture 14 shows the substation main earthing conductors. All substation should be installed with these copper tape conductor along the walls of the substation. It is usually called the substation main earthing conductors. These conductors are terminated to a main earthing busbar.

In this case, the earth busbar has not been installed yet. However the location is as indicated by my comment on the picture.

The main conductor running horizontally on the walls will be cut at the location shown. The busbar will be installed there. The cut horizontal conductors (now it has become 2 lengths after the cutting) plus the three vertically mounted conductors already there will be terminated to the earth busbar using properly sized bolts, nut and spring washers.

Note: You can also see more pictures of electrical wiring by visiting this post, Pictures of electrical wiring.


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