Underfloor trunking below structural rebars

Below is a picture of a somewhat "improvised" installation of underfloor uPVC trunking within the structural rebars of a floor slab in a workshop building under construction.

Picture 1: uPVC trunking installed below structural rebars

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I have published quite a number of pictures on underfloor trunking systems.

Below is an example which was been posted in May 2010.

Picture 2: An under trunking system at a highrise office building



These underfloor trunking systems, together with their floor draw boxes (i.e. junction boxes) and floor service boxes, have so far been installed inside the concrete screeding of the concrete floor.

In this installation method, the reinforced concrete floor slab is constructed first.

However, the construction of the concrete floor is not yet completed with the completion of the reinforced concrete.

A layer of concrete 50mm to 75mm thick is to be poured and leveled on the finished reinforced concrete to make a finished concrete floor. This layer is called 'concrete screeding'.

It is within this top concrete layer that an underfloor trunking system is installed, or "embedded" as some people call it.

However, in the new picture that I showed above, the underfloor trunking is not installed in the screeding layer (In fact there is no screeding layer here).

The finished floor level here has been designed to be just 50mm above the top of the top of topmost reinforcement steel bars (called "rebar").

With the size of the uPVC trunking of 75mm wide x 25mm height, there would only be "approximately" 25mm thick of concrete above the uPVC ducts.

This concrete thickness is insufficient and it can eventually crack even in a "light duty" environment such as office floor. It will not last very long here ... it's a workshop.

So in this case the contractor had no choice but to install the trunking between the steel rebar mesh. If it had been two layers of reinforcement provided, then the trunking would be installed between the layers.

Picture 3: Close view of a service box opening

As you can see there are also added reinforcement bars around the opening for the underfloor service box.

When I took this picture the structure engineer has not yet inspect the underfloor trunking installation work.

They have inspected them once and had a few major comments.

One of the comments that I wish to share with you is that the uPVC trunking should not be touching the steel reinforcement bars.

The photo below shows how the installation was before it was corrected.

Photo 4: uPVC trunking touching steel reinforcement

At the areas where the trunking touches the rebars, the grip of the concrete material onto the reinforcements would be weaken. This may weaken the strength of the finished reinforced concrete.

How much weaker? Well, I did not really ask. My guess was that even the site structural did not really know "how much weaker".

Photo 5: The corrected trunking installation

In the above picture, the trunking installation was adjusted to leave some gap of around 15mm or more between the trunking and the steel reinforcement.

You can still see the rust marks on the trunking where they touched each other earlier.

Beginners please do not get confused here. The white rectangular boxes connecting the underfloor trunking are not the real underfloor junction boxes or service boxes.

They are just some polystyrene foam materials (the same material some people uses as refrigerator insulators) that are used to create openings for the real junction and service boxes that will be installed at a much later date.

If the contractor installs the boxes now, they will be damaged in a very short time.

OR STOLEN! ... I can almost feel some readers quickly nodding their heads in agreement ...

Okey guys. This is all I can write today. I will post a few more other pictures on this soon.

Copyright http://electricalinstallationwiringpicture.blogspot.com Underfloor trunking below structural rebars

Exothermic welding: Cable to cable connections

Just a few pictures today … on exothermic welding joint of earthing copper cables.

Picture 1: Cable-and-mould set-up for a cable-to-cable exothermic joint

(Click on the picture to enlarge it.)

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The above picture shows the set up for a cable to cable connection.
For the uninitiated, I have labeled the components in Picture 01 and show them again in Picture 02 below.

Picture 02: Exothermic welding process set-up labeled

(Click on the picture to enlarge it.)

I will not write much today and I have serious doubt that I will be able to write long posts again in the near future.

The best I can do is to show you some pictures. When I have more time I will write longer.

Note that the part that I labeled “explosive powder” is not really explosive powder. Well, It IS explosive, but it is not an EXPLOSIVE.

It is actually some powdered mixture of copper oxide and aluminium. When ignited, the mixture produces a very high temperature reaction that molten the copper and aluminium components which then flow into whatever cavities between the conductors to be joined, as well as form a thick layer of alloy envelope around them.

This you can see in Picture 07 below.

Picture 03: Just a closer view of the mould.

(Click on the picture to enlarge it.)

Picture 04: A shot during the combustion

(Click on the picture to enlarge it.)

Picture 05: A cable-to-cable joint still red-hot

(Click on the picture to enlarge it.)

For the curious, the earthing cable conductors in the pictures are 95 mm.sq stranded copper cables.
This installation was part of an earth mat type earthing system. High voltage substations for voltages 33kV and above usually have some sort of “step voltage” protection and the earth mat or earth grid is part of the “step voltage protection system”.

For beginners who have no idea at all of what all this means, have no worry. I will send a post or two on “earth mat” and “step voltage“ soon.

Picture 06: A completed cable-to-cable joint

(Click on the picture to enlarge it.)

Picture 07: A closer view of the finished exothermin joint.

(Click on the picture to enlarge it.)

Okay, folks. See you in the next post.

Jimmy Lee Wan Seng
(Information Trader)

Copyright http://electricalinstallationwiringpicture.blogspot.com Exothermic welding: Cable to cable connections

Fire Riser Rooms

Below you can find two pictures showing fire riser rooms at a multi-storey building.

Picture 1 - Fire Riser Room

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Here you can see wet riser pipes and hose reel pipes.

For the uninitiated, wet risers are vertical pipes that are always under pressure with water.

This means that any time a fire occurs in a building, you will have water to fight the fire immediately. You can connect the flexible hose provided in the riser room or the riser shaft at each floor to the landing valve of the vertical wet riser pipe.

The hose reel system is also part of the fire fighting system in a building.

To be precise, this is what you can and will use to fight fire when it happens. The wet riser are designed for use by firemen.

The hose reel pipes are also kept under pressure at all time. The system are provided with pumps that operates automatically to keep the hose reel piping under adequate constant pressure at all times.

The water jet produced by the hose reels are however only adequate to fight small fires. That is why firemen will not use it. It is designed for use by building occupants BEFORE firemen arrives.

Dry risers, on the other hand, are similar to the wet riser piping, but without the water. They are simply vertical pipes without water. The water needed to fight fire will be from the fire trucks brought in by the firemen when they arrive.

The above is a highly simplified brief of the fire risers to give casual readers some meaning of what they are.

I will post a more detailed explanation of the fire fighting systems for buildings in a near future.

Picture 2 - Chilled water pipe installed inside a fire riser shaft.

Here you can see a vertical  pipe that may not belong here.

This is a chilled water pipe.

Some fire authorities may not allow other services to be installed inside the fire riser shaft. It was allowed in this project.

Copyright http://electricalinstallationwiringpicture.blogspot.com Fire Riser Rooms

Architectural Lighting

I do not know how many readers will like this picture, but I like it.

Picture 1 - A nice picture

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A few may even question whether it does qualify into the category of electrical pictures.

This is actually a photoshot of the top of a bridge at night. The bridge shines out nicely as it reflects the light rays from light sources installed at ground level.

It is true that this is actually an architectural work.. architectural lighting to be precise.

However, the architects need electrical engineers to to handle these high power lighting, especially since the lighting is actually installed at public areas.

Picture 2 - One of the light sources at ground level.

I have been silent for many months from this blog. Today I am coming back.

I however have not decided yet what themes I am going to use to upload pictures this time. So I decided that I should start slow and use whatevers pictures that I can snap around me.

That is why I show you this picture.

The are a number of nice bridges here and I can try to take a few shots.

See you in the next post.

Copyright http://electricalinstallationwiringpicture.blogspot.com Architectural Lighting