Saturday, March 8, 2014

Electric cable bridge

Continuing the tradition of sharing engineering knowledge through pictures, today I am sharing with you some pictures of cable bridges for electrical cables.

Picture 1 – An existing electric cable bridge

(Click on the picture to enlarge it)

================= RELATED ARTICLES: Underground street light cables |  Underground electrical manhole | Compound lighting storage yard  | Compound Lighting Installation Pictures  | Feeder pillar single line diagram  | Bollard light pictures  | Feeder pillar hazard pictures  | Compound lighting foundation size Architectural Lighting | Electrical installation pictures

About the author:

When the idea of this post popped up in my head, I typed in the Google search for the word "cable bridge".

The results were not what I expected. Instead of bridges for electrical cables, the results were mostly on real bridges employing suspension cables to transfer the bridge loads to the bridge columns and the foundation

Then I tried "electric cable bridge", the results were a little better. Google was still not giving me much information electric cable bridge that I need.

Lastly I keyed in "electrical cable bridge". The results were just almost the same as the electric cable bridge.

I was disappointed. I guess not many people need information on bridges for electrical cables.

So the title of this new post was confirmed by the lack of websites providing information on this topic.

Well, I am not going to write that much either. I am just going to share with you a few photos on this matter.

Picture 2 – Location of the new cable bridge

(Click on the picture to enlarge it)

The M&E manager of the main contractor in one of my earlier projects came to my office one day and said, "I cannot complete the underground cable containment for the authority by the end of the month."

I said, "Then you have a 200,000 dollar per day of penalty on your head, my friend. That is one million per week. It's in your contract."

Then he explained to me that there was a very small stream crossing the route of the 33kV underground cable containment where he was going to lay the underground ductbank.

The location of the stream crossing was outside this contract package boundary. Not many of us (including me obviously) have actually done a thorough inspection of the area yet since the construction of that part of work has not yet started.

To make it worse, this contract has a peculiar schedule which requires that the authority's 33kV substation should be handed over to them at the beginning of the project instead of at the end as was the usual practice.

To make the story short, this cable bridge was overlooked in the design drawing and now the design consultant need to quickly come up with a complete design for the electric cable bridge.

I assisted with whatever I could to provide the consultant's design office with information so that they can complete the design quickly.

Part of the assistance was to go around taking pictures of existing electrical cable bridges. This could help us design a similar one that would be acceptable to electricity supply authority.

Since the cable bridge was to be part of the 33kV cable containment for the authority's incoming supply cable to the project, then the cable bridge was also to be handed over to them after completion.

I am showing to you here a few of the pictures that I took, including the new cable bridge that we built.

Picture 2 above shows the location of the small stream along the route of the 33KV authority supply cables.

Observe the existing water supply pipe over the stream.

After some investigation, we found out that the pipe was installed by the water supply authority five to six years earlier as a provisional infrastructure for future development because there was a huge empty land area in the vicinity.

Picture 1 at the top of this post was one of the existing electric cable bridges that I visited.

It was carrying 33kV supply cables for a large residential are there.

Picture 3 - A view of the cable bridge from below

(Click on the picture to enlarge it)
Note the large residential development behind the bridge.

When I said "large residential development" it does not mean that the area only has residential building such as high rise apartment, bungalows and terrace houses.

Nowadays large residential developments are developed complete with their own commercial centers at strategic locations throughout the development.

So from electricity supply point of view, the supply infrastructure must be adequate for the KW demand of not just the planned development, but also for any unanticipated further growth as a spin-off from this development.

Picture 4 - A view of one end of the electric cable bridge

(Click on the picture to enlarge it)
This is one of the cable bridges.

Observe how the red PVC ducts leave the bridge and enter the large above-ground cable trough.

Well, this is not an above-ground cable trough, but it needs to come up above ground as it approaches the bridge end in order to protect the cable ducts leaving the bridge.

Note that this is a 33kV cable ducts as is obvious in the following picture.

Picture 5 - Front end view of the cable bridge

(Click on the picture to enlarge it)
Observe the protection measures employed in order to prevent the public from climbing onto the bridge or access the PVC cable ducts.

I know that some readers think that I made a mistake by typing "PVC" cable ducts.

Many people have the opinions that normal PVC ducts is a bad choice in this type of applications because the ultra-violet (UV) ray from the sun will turn the PVC ducts into "crispy biscuits" relatively quick.

Actually that was my opinions too.

But the electricity supply authority have a very different opinion and they have thousands of bridges like this installed throughout the country.

I think their experience outweighs our opinions on this matter for this particular application.

In any case, the new cable bridge in my project was to be handed over to them.

The design of the new electric cable bridge itself had to be submitted to their office for approval prior to construction of the bridge or fabrication of the steel structure at the factory.

Picture 6 - Another view

(Click on the picture to enlarge it)
I think this is the best single view of the existing bridge because it the whole complete system that is viewable.

Picture 7 - The new electric cable bridge has been completed

(Click on the picture to enlarge it)
Picture 8 - This give an overall view of the cable bridge "system"

(Click on the picture to enlarge it)
Here you can see the overall "system" of the cable bridge.

Beginners please note the partially above-ground cable trough connecting one end of the bridge to the underground cable-pulling manhole.

The other side of the cable bridge was implemented similarly.

Observe at the far background in the picture that there was a long red-and-white "thing".

This was new jersey barrier units lined up along that side of the main road.

It was along this main road that the 33kV incoming supply of the authority would be taken from via a loop-in loop-out method.

Picture 9 - Cable bridge construction in progress

(Click on the picture to enlarge it)
This is the last picture for today. I show this one for those who are interested in the bridge column and foundation.

You cannot see the foundation, but it was not a pile-type. The foundation was constructed as a simple large plate without piling.

Okey guys. That is all I can give today.

See you again in the next post.

Copyright Electric cable bridge