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Join Date: May 2011
Posts: 73

Damage In Cables

05/03/2012 12:35 PM

Iam handling Electrical power cables laying package, I have seen in many cables the outer sheath got damaged and armour is seen by naked eyes.

i heared tat not to use M-SEAL to cover the outer sheath.....

pls sme one clear me why should not use M-SEAL or what can we use to cover the damaged outer sheath.....????

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#1

Re: Damage In Cables

05/03/2012 2:20 PM

I don't know what M-Seal is, but aside from preventing the damage in the first place, you may want to look into this:

http://www.dowcorning.com/content/electrical/electricalrestore/

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#2

Re: Damage In Cables

05/03/2012 2:33 PM

The obvious answer is because M-Seal is epoxy-based and dries rock-hard and the insulation is not; therefore any flexing of the cables due to expansion-contraction, ground motion, etc. will result in the cracking of the bond that was formed.

The engineering answer is that your client paid good money to have a protective barrier over the cables and now it is breached which will lead to a shorter service life and problems in a much shorter time than he paid for. If this is for anything other than low-voltage cable then the outer covering, inner sheath and armor are all part of a complex graded insulation system that cannot tolerate any breaks in it.

The proper "repair" is to use an approved splicing kit to replace the bad section, or pull the entire section and re-lay it properly. An even better idea would be to review your procedures for installing your cables so as to prevent the damage in the first place.

"How come there is never time to do it right, but always time to do it over?"

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#3

Re: Damage In Cables

05/03/2012 2:39 PM

Follow the wiring standards for your location and that your electrical engineer or licensed electrician tells you. We do not know the severity of the cable damage or if these power cables will be strung between transmission towers, underground in conduit, submerged between islands, rising 25 stories of a 50 story building, or just between decks of a submarine.

It is good that you recognize that somebody else should decide what should be done, if anything, with these damaged cables. We are not your authority to answer this question.

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#4

Re: Damage In Cables

05/03/2012 7:10 PM

Raychem do a heat shrink bandage for this exact problem.

http://raychem.te.com/CableProtection.asp

But as has been said, with correct installation the problem should have never occurred in the first place.

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#5
In reply to #4

Re: Damage In Cables

05/03/2012 8:11 PM

In fairness to the OP, there are many, if not most, parts of the world, where people have no choice but to work with what they get. Going back through the supply chain may not be an option.

Just sayin'...........................it happens.

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#6
In reply to #5

Re: Damage In Cables

05/03/2012 9:47 PM

Yes, it does happen. When you don't have a choice though, why ask what should be done?

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#7

Re: Damage In Cables

05/04/2012 12:53 AM

How old are the cables? If they are young and laid recently and have undergone outer sheath damage, then you must contact the manufacturer to seek an explanation. This, of course, is subject to the condition that the cable has been laid strictly as per norms and cable laying techniques and has not been damaged during laying. M-seal cannot be used as has already been explained well by other colleagues on this forum. It will crack as the cable heats up due to flow of current in the cable.

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#8

Re: Damage In Cables

05/04/2012 10:33 AM

If these are PVC sheathed cables I would use self-amalgamating tape. If the cable has a bitumen based tape sheath replace with a similar bitumen tape and warm. If the cable is in open view find a new job.

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#9

Re: Damage In Cables

05/04/2012 3:17 PM

Mohsinhamid wrote:

"I am handling Electrical power cables laying package, I have seen in many cables the outer sheath got damaged and armour is seen by naked eyes."

HEY! Wait a minute. you are saying you are operating cable laying equipment and have seen MULTIPLE instances of cable sheath damage. Why didn't you stop the first time and report it to prevent a recurrence?

Having supervised cable laying crews myself I can tell you repeat occurences would never have been tolerated on my watch. The crews responsible would either have been given training in proper handling or replaceed with better crew.

I was also responsible for cable fault detection and repairs so any unrepaired sheath damage would quickly have ended up as a fault locate and repair job in my baliwick. Pretty hard to explain away sheath damage on a job I supervisei installing.

Both Raychem and 3M provide cable splice kits to repair or replace cable insulation and they provide good instruction on how to use the product. Instructional videos were available in my time so I would expect something similar is available today.

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#10

Re: Damage In Cables

05/06/2012 1:20 PM

Thnks every one for your valuable answer, the damage i had seen is not big, its a 2 inch of outer sheath opening and armour is seen, the cable voltage is 6.6kv, do its necessary to use splicing kit for tis damage or any other option available....

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#12
In reply to #10

Re: Damage In Cables

05/06/2012 2:30 PM

You have not said what the cable sheath made of. The armour is there to protect the cable from damage by others not the people who are laying it. However damage does occur during laying and it is important that the damage is reported to the supervisor and not just buried. If the cable is underground the sheath stops the armour from corroding, if damaged it must be repaired to stop water getting in. There are sheath repair kits manufactured and when available they should be used. If they are not available ensure the sheath is well cleaned then apply several layers of self amalgamating tape allowing plenty of overlap each side of the damage. This is assuming the sheath is PVC or similar. Try and make sure damage does not happen but do not make cable laying staff frightened to report damage.

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#11

Re: Damage In Cables

05/06/2012 1:39 PM

Dear friend the outer sheath is just an outersheath. it meant to just prevent superficial damage. if there is no serious damage to armour do not worry. why we are providing armour?

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#13
In reply to #11

Re: Damage In Cables

05/06/2012 2:58 PM

Good grief!!!

The outer polymer sheath is a moisture barrier as well as a sheath to give additional mechanical protection. The polymer sheath is smoother than the armor braid so the cable can slide into a conduit easier. The plastic moisture barrier is useful when cable is directly buried. This means the armor is not in direct contact with soil and moisture that can create galvanic corosion of the armor. When you bury any metal in soil then dig it up a year or two later there is corrosion found.

Damage such as you describe is not minor in my opinion. It will lead to premature cable faults and failure.

No you do not have to cut and splice in a new piece BUT you do need to replace that outer polymer coating to re-establish tie moisture barrier. Since I am not familiar with the brand names you have ready acces to locally the easiest method was to refer to the splice kits which contain the correct sealant tape suited for re-wrapping the outer jacket. Ordinary black electrician's tape is not adequate. Your local supplier should be able to provide the right kind of sealing tape regardless of what local name is used. But a hard epoxy is not suited for direct burial.

In North America we call this protective tape self amalgamating plastic tape or SAP for short. It is a butyl compound that sticks to itself and creates an impervious coating within 24 hours. If the outer plastic is scraped offf but the armor sometimes also referred to as a concentric neutral is not harmed or the tinning scraped off then you can repair the cable jacket by wrapping with the butyl tape. Follow the instructions.

If the abrasion was caused by pressure that deformed the concentric shape of the cable you have another potential problem. The concentric shape of the cable construction has an inherent capacity of the dielectric. If the cross section of the cable is distorted into an oval; the capacitance will also change. A fault may develop at this point some time in future years.

We had one industrial subdivision with 3 phase buried 27,600 volt distribution. Every month we had yet another fault materialize. After a while we concluded the problems were due to inferior workmanship by the crew that buried the cables. We made very sure the word got out in the industry that this was one contractor to avoid in the future.

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#14
In reply to #13

Re: Damage In Cables

05/06/2012 3:24 PM

You ended with precisely the point I wish to make. Three days ago these cables were laid (presumably underground) by a work crew that noticed damaged cables but did not stop to repair the damage before installing this cabling. This work crew is establishing their reputation with this cable installation. Hopefully they get their just rewards.

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Users who posted comments:

BB Raina (1); elnav (2); kramarat (2); mohsinhamid (1); pravindhameliya (1); Rainmain (2); RAMConsult (1); redfred (3); TonyS (1)

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