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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1 comment:

John Brett said...

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