Friday, January 15, 2010

Electric Cable Drum Pictures

Why would I want to show you pictures of electric cable drums? Because I have a story to tell.

Picture 1 – Damaged cable drum


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The work involved the cable laying works for the lighting of a car park area and the compound lighting of the high-rise building under construction. The civil works for the car park was progressing fast. Therefore, the electrical contractor needed to start the cable work soon.

They ordered five drums of XLPE insulated, steel wire armored copper cables with a length of a few hundred meters per drum. The cable sizes ranged from 6 sq.mm 4-core up to 50 sq.mm.

One afternoon just before a long public holiday, the transport truck delivering the cables arrived at about 6 PM.

Since it was on the eve of a popular holiday, most of the main contractor’s workers and all their project officers already left the construction site. Usually these people work until at least 7 PM.

Of course, all the security personnel were still on duty. So the transport was allow to enter the construction site to deliver the cable drums.

A few of the electrical contractor’s people were still at the site including a supervisor. The engineers have all disappeared. However, the personnel in charge of the material’s store (i.e. the store clerk) were still at work. The store were manned 24-hours with the sub-contractor’s own men to look after their materials at the construction site.

Upon arriving at the store, the transport truck driver asked that a forklift be used to unload the electrical cable drums. There was a forklift just nearby the store. However, it belongs to the main contractor and those allowed to drive the forklift have already left the site for the long vacation.

So, no forklift.

The truck driver asked for other means for unloading the cables drums. There were actually a number of machines at the site that could have been used including forklifts, a number of backhoes of all sizes and excavators.

However all workers authorized to handle these main contractor’s machines have all gone home.

After a while with no success of getting a machine to unload the cables, the truck driver asked the store clerk if he could speak with the supervisor himself. The supervisor was at that time busy with his own work at the 30th floor of the building under construction.

He was in no rush to come down himself because the lift operator for temporary lift has also has left the site. Walking down from 30th floor was not something he would do for fun.

The truck driver was getting really irritated. He might have shouted to the supervisor or said something offensive. The supervisor angrily said, “Why don’t you just throw the cable drums off your truck!”.

So, the truck driver did just that. He rolled off the cable drums off his truck in front of the electrical contractor’s site store and left the site. Unbelievingly, the site clerks actually did sign the delivery receipt of the cables.

A few people saw the event and reported it to the engineer in charge after the holiday was over.

Photographs of the cable drums were taken, a few of which are what I uploaded here for you to see.

The engineer rejected the cables and the cables that were already delivered were not allowed to be taken out of the construction site until the replacement cables arrived.

The reason was to prevent the electrical contractor from re-drumming the cables and deliver again to the site as allegedly different new cables just off the manufacturer’s factory.

This is a true story. It was a joke that was carried around the site for quite a few weeks.

Now let us go to the moral of the story, which is cable handling.

Picture 2 – The integrity of these cables is now a suspect


Picture 3 – The cable on this drum may not really be damaged, but who knows how long will it work without problems?

Nobody can guarantee, not even the cable manufacturer.


Picture 4 – This cable drum was nearby, but it was not part of those dropped of from the transport truck.



HOW TO HANDLE CABLES IN DRUMS

Dropping off cable drums

It is very important that great care is exercised at all times when handling cables.
Every precaution should be taken to avoid dropping a drum of cable. Dropping off cable drums, even from a short height, will flatten the layers of the cable nearest to the barrel of the drum.

Depending on the length of the cable, the type of the cable involved and the height of the drop, the weight from the outer layers can cause damages to the inner layers that are very difficult to ascertain.

Similar distortion to the cable will also occur if the drum falls on its sides.

Rolling the drums

When rolling the drum into position it is essential that the drum rolls smoothly in the direction of the arrow painted on the side of the drum.

If this instruction is not followed, slack cables will accumulate towards the inner turns and this may result in damages to the cables.

Removal of the wooden battens

Wooden battens around the cable drum should be very carefully removed. Suitable tools should be used for this purpose.

How to dispose the cable off the cable drums

When a drum is in position, it should be mounted on jacks and disposed in such a way that the cable is pulled off from the bottom and not over the top of the drum.

It is preferable to mount the drum at one end of the cable run as close as possible to the edge of the cable trench so that the cable can be pulled off in a continuous manner on rollers in trench and is in its final position when the last turn leaves the drum.

At times, this procedure cannot be followed because of the excessive length and weight of the cable run. In certain cases, it is because of difficult obstructions such as large diameter water pipes under which the cables have to be threaded.

In case like these, it may be necessary to position the drum at some other point along the cable run.

The cable is then laid off on the ground near the drum in a series of loops, one above the other in the form of a figure eight, crossing the cable back and forth on itself.

After the whole length has thus been removed from the drum, the inside end of the cable will be on top.

Then the cable can be pulled along towards its final position on rollers in the same manner as if the cable was coming off the drum itself.

Whichever procedure is adopted by the contractor, sufficient care must be taken at all times to ensure that the cable is not twisted and that the turns are well above the minimum bending radii of the cable size.

For cables with operating voltages below 22 kV, the minimum bending radii may be taken as follows. However, other specifications or instructions that may be provided by the manufacturer of the cables being installed can be used if available:

For sizes up to 50 mm overall diameter – Minimum bending radii: 12 x overall diameter

For sizes 50 mm and above overall – Minimum bending radii: 20 x overall diameter

Wire cable stockings with an eye at one end should always be used when pulling cables with pulling ropes.

The pulling ropes should never be tied directly to the cable ends.


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Network cable trays

One or two readers may think that the pictures of network cable trays and trunking may be a little bit out of place in this blog. However, when it comes to construction of new buildings, it has become one of the usual practices to include the installation of cable management infrastructure for information technology (IT) services under the electrical works contract.

Picture 1 – Riser cable tray for the computer network cabling



The above picture was taken at an office building under construction. The white-colored cable tray is located inside the ELV riser shaft. ELV stands for Extra Low Voltage.

Most of the time there are number of services under the category of electrical services inside a multistory. Even some parts of the fire protection system are categorized under the electrical services such as the fireman intercom.

In multi-storey buildings, these ELV services are provided with their own riser shaft and the rising main for all the ELV services are located here. This usually include telephone, public announcement, fireman intercom, closed circuit TV (CCTV), master antenna TV (MATV) or satellite TV, and all types of inter-floor audio-visual communication systems.

When the building-wide computer to computer communications came to be widely used, then the need to provide for them became part of the design criteria for building designers and electrical consultants.

However, usually the details available to the designers during the design and construction of the building are not enough for a complete and proper implementation of the IT systems. For some building projects who tried to fully implement it together with the main building contract, various problems have been common.

Some projects even faced delays in completion and handover because of this IT system.
Partly because of this reason, many owners choose to implement the IT system on their own after the building handover.

The main contract of the building works then is instructed to prepare the cable management infrastructure to accommodate the IT cabling that would come after the completion and handover of the building. This infrastructure usually includes all the rooms, spaces, cable risers, trays, conduit and trunking for the computer network.

Even the server rooms are usually prepared and ready with raised floor system, 24-hour air-conditioning system and suitable fire protection systems.

The only scope of work left to the IT contractors is the cabling and wiring installation, and the computer hardware.

That is what the contract arrangement has been for this building contract. The white cable tray is for the computer cabling. A complete management system infrastructure has been prepared including the underfloor trunking system.

I do not have the digital copy of pictures for underfloor trunking system. You will be able to see them in this blog soon. However, two more pictures below shows the normal trunking that has been installed (actually the work was still in progress when these pictures were taken).

Picture 2 - Computer cable trunking inside riser shaft



Picture 3 – Computer cable trunking coming down from ceiling.




Copyright http://electricalinstallationwiringpicture.blogspot.com/ Network cable trays

Thursday, January 14, 2010

Electric Meters

Who would be interested in the pictures of electric meters? I do not know either. However, electric meters are an important component in electrical installations. That is how the energy consumed by an installation is measured and recorded. With this record, the owner of a factory, as an example, can be charged for what he uses.

Picture 1 – Single phase house electric meter


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I set up this blog about three months ago. After one or two posts, I started having difficulties in allocating the time needed to accelerate its development progress into speed.

Only now I can start looking this blog again. So I will start rebuilding it with materials that I already have in my collections. I have lots of pictures. However, I do not want to dump them all here.

There should be a story to it, like a script so that the pictures will have more useful meanings to the readers who look at them.

Again, as I already said before, this blog is for beginners. Beginners do not necessarily mean young people or students.

Building managers who need to know a little bit about a few electrical things in order to solve a few management issues, or an accountant who desperately need to know how some electrical components look like because one of her client’s accounts shows a huge price tag for those components.

This blog is for these types of readers. How I arrange and present the materials here will have this type of audience as the main objective.

Now and then, the materials presented may get “heavy” or highly technical. Many times this cannot be avoided. Components like distance protection relays cannot be explained with descriptions anywhere resembling those for simple components such as 13A switched socket outlets, or the electric meters as in the title of this post.

However, for those readers who “desperately” need to know something but cannot find it here and do not know how to dig it out from the internet “jungle”, you can just leave a short comment on this blog.

You can get my assurance that I will answer your questions as soon as I can. That means two days the fastest, and one week at the worst case.

Now let us get back to the electric meter topic.

I am not going to talk too much on this component today because it is the first day I am back to this blog. I will update this post with additional information soon.

This electric meter is from a 3-bedroom medium-cost terrace house unit. This type of houses almost always uses a single phase supply. So this meter is a single phase meter.

You can see that the meter is mounted on a wooden panel. This is very conventional. The oldest meter panels that I have ever seen already uses this type of meter panels and they are still used even today.

However, nowadays a few other types of meter panels are in the market that are acceptable to the supply authorities. You will be able to see the other variations here in future.

The meter panel in the picture may look simple to some readers, but since we are on the topic, I would not want any reader leave this post without a basic understanding of how those things on the panel work.

I have explained a little bit about the meter itself.

However there are two more major components on the board: one you can see and the other you cannot see in this picture.

The Cut-out Fuse

The one you can see is a cutout fuse, which is the black component beside the meter. The cutout fuse is just a fuse. When the electric current flowing through the fuse exceed the rating of the fuse, then the fusing element inside the black casing will blow, cutting off the supply to the meter.

So the meter does not run when the house is without power.

Picture 2 below show a closer view of the meter and the cutout fuse.

Picture 2 – Closer view of cutout fuse



There are two parts of the cutout fuse, which you may see by closer observation of the picture. One is a top part, which is inserted into a lower part. The other is the fuse holder that forms the base that is screwed firmly onto the wooden panel. One of the incoming supply cables is connected to the cutout fuse and it is terminated at the lower part, the fuse holder.

The fusing element, which is a thin conductor wire that melts and breaks the path of electricity to the meter (and therefore to the house electric distribution panel), is actually installed inside the top part of the cutout fuse assembly, the “fuse carrier” as it is often called.

If the house occupant do not pay the electricity bill within the time as required by the electricity supply company, then the company may cut off the electric supply to the house.

This is where they cut off the supply, the cutout fuse. That is why it have been called that way, “ CUT OUT”. The supply company just pulls out the fuse carrier from the fuse holder and takes it back to their office.

The Neutral Link

The second component that is mounted on the meter beside the meter unit is called the neutral link. I am sorry you cannot see it here in this picture. I will upload another picture of a meter panel that will show this neutral link.

As you can see, there is a pair of incoming black cables to the meter panel. One of the black cables is connected to the cutout fuse as already described above.

The other cable is connected to the neutral link. This is the neutral cable, or also called “return cable”, or “return wire”. While the one connected to the cutout fuse is the “live wire”, or the “phase conductor”.

The neutral link is a connection method similar to the fuse, but its connection is without the fuse. It is done with a solid connection bar. Therefore, this side of the electric circuit cannot automatically break the circuit.

Then why is it provided there? This is for the purpose of maintenance and repair work. Sometimes, for safety reasons, a repair work necessitates that the house wiring is fully isolated from the supply company’s incoming circuit. In that case, both the cutout fuse and the neutral like is taken out, disconnecting the house wiring from both sides of the incoming supply cables.

The meter panel cabling

There are four cable connections to the meter panel.

1. The incoming phase conductor (one of the two incoming supply cables) connects to the cutout fuse terminal.

2. The second incoming cable is connected to the neutral link.

3. Phase cable from the meter unit outgoing phase terminal to the house distribution panel.

4. Neutral cable from the meter unit neutral outgoing terminal to the house distribution panel.

Within the meter panel itself, also four cable connections are needed with two other cables involved.

These are to link both the second terminals of cutout fuse and neutral link to the incoming meter panel terminals.

The cabling work that is visible from the front of the meter panel is basically incoming cables.

Other cables are hidden below the wooden panels as much as possible. That is why the panel is constructed with some hollow space underneath to contain the cabling work so it is hidden from view.

The mounting location

The height of the meter panel mounting is also decided so it is above the reach of access by hand. This arrangement is necessary for safety reasons. Anyone who wants to work on the panel needs a ladder of some kind.

This is necessary because most of the time the meter is located at the front of the house to facilitate the billing by the electric company. But this location can present a real shock hazard if the panel is not effectively placed out of reach.

Mounting height is only one method. Other means of placing it out of reach such as locking inside a small cabinet with glass window is also an acceptable by the supply authority.


That’s all the spare time I have today. I think I have covered most of the issues on the electric meter panels. If there is anything left, I will pick it up again in the next post. There are one or two more pictures on the electric meters that I need to upload also.

See you.


Jimmy Lee Wan Seng


Copyright http://electricalinstallationwiringpicture.blogspot.com/ Electric Meters