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Thread: Life expectancy of primary and secondary power???

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    Senior Member USIC1's Avatar
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    Default Life expectancy of primary and secondary power???

    Was curious if anyone has any RELATIVE knowledge of years of service (life expectancies) of buried electric cables!?!?!

    I know they are more frequently replaced throughout older neighborhoods then telco, and tv, and also wonder if the material used today allow for a greater lifespan...

    Wonder if its because of older concentrics and the deterioration of those outer bare ground strands, or even with the non-concentric that a tole is taken from heat and current (molecular flow) compromising the core over time deteriorating the metallic element or even the insulating content???

    Does a decision to replace ONLY come from random outages on older cable, or is there some form of inspection that calls for replacement prior to fault occurences???

    Do we have any brains around here that have delved into this technicality???

    Last edited by USIC1; November 8th, 2009 at 11:00 PM.

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    Default Re: Life expectancy of primary and secondary power???

    Actually a really good question. In my area it seems like they wait for the primaries to start faulting alot before replacing them. The primaries they are replacing are form the 60's and 70's. My guess would be theses older outer concentric cables wouldn't last as long as the jacketed primaries because the new ones are protected from the elements.

    It sure would be nice if the tel,tv, and elec companies would work together and replace all their lines at the same time. Normally the electric company will come in and replace all their stuff and then the next year the phone company will come in and replace their stuff.

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    Default Re: Life expectancy of primary and secondary power???

    I know in my area once the cable start faulting they test the cable by deenergizing the cable then they apply 30k volts through it..if it blows then they will put a thumper on the cabler to identify where the cable blew out and they can also detect how many spots it blew. Then they will dig up the cable to resplice or repair then recheck the cable. If it still will not hold 30k volts then they call Trafford in to replace the whole span. This is found to mostly with concentric cable but I have seen the newer cables fail as well.

    Also I have been told that they look to inspect the cable when it reaches 25-30 years old. Guess that the time frame that seems to be when it starts to fault.

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    Default Re: Life expectancy of primary and secondary power???

    it's mainly the older subdivisions in my area that get the new upgrades.....but usuallly just a main from transformer to transformer gets replaced not a whole section unless there are alot of troubles....i'm curious to know the answer to this question also.....???
    wise men talk because they have something to say and fools because they have to say something....plato

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    Default Re: Life expectancy of primary and secondary power???

    Where I am it's about 25-30 years in reality, but they were supposed to be on a 50 year expectancy. It all boils down to load. If the system is pulling more juice than it was expected to, the lines fail faster and get replaced. Oddly its the core that fails more often than the concentric ground (would have thought it the other way around). Never reallythought about why much, but I guess now it's reseach time. I needed a new project. Thanks USIC1... I'll report back after I learn more.
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    Default Re: Life expectancy of primary and secondary power???

    I think SIC1 needs to go in for a whiz quiz. He's actually making sense.
    STRESS: The confusion created when one's mind overrides the body's basic desire to choke the living daylights out of some idiot who desperately deserves it.

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    Default Re: Life expectancy of primary and secondary power???

    Quote Originally Posted by beyond help View Post
    I think SIC1 needs to go in for a whiz quiz. He's actually making sense.
    Disturbing huh?
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    Default Re: Life expectancy of primary and secondary power???

    Yes to all of the above... from what I've learned the cables SHOULD last about 30 years, but several factors involved here: type of cable (jacketed vs outer concentric), load in a particular area, soil quality (if it's more corrosive to the cable buried therein regardless of makeup), whether the cable has stayed electrified consistently, and wet vs dry environment. Once the cable is de-energized for any period of time, having been that way for potentially years, the change of state may cause it to lose integrity and re-energizing it will cause it to blow. The electric company I work for MUST test the cable before re-energizing it (called "hi-potting" - testing the high potential of the cable) to know it is sound before applying a load, that it won't fault again. Doesn't always predict what happens though... the crew may fix the fault, re-energize it after hi-potting it, and 10 minutes later it faults again, sometimes in the same exact spot. [Hence you'll get to locate the exact same spot more than once, it re-faulted is probably the case~!]

    Replacing a cable entirely is a calculation I'm not privy to... I do know they keep track of faults on particular areas, if it goes bad a certain number of times they SHOULD replace it - magic # was 3, we guessed years ago, but I am not certain of that. Ask Big Boots... how many times did that cable on Greene fault before they replaced it that time I came to help you? Like, 12???

    I have seen a trend where the util co's will trench new cable together. But doesn't some municipalities specify that particular sections of easement belong to a certain util? I heard that's how it's done in the south...

    And of course, lastly, there's the cable injection process that Utilx does... they insert a pump at a transformer that squeezes a gel through the jacket, so that by time it reaches the next transformer all gaps have been filled in with the gel, effectively sealing it and making that section good for another (they guarantee or they fix it themselves) 20 years.
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    Default Re: Life expectancy of primary and secondary power???

    ~
    Last edited by wet_boots101; November 10th, 2009 at 01:19 PM. Reason: oops = hit submit twice
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    Default Re: Life expectancy of primary and secondary power???

    Quote Originally Posted by wet_boots101 View Post
    I have seen a trend where the util co's will trench new cable together. But doesn't some municipalities specify that particular sections of easement belong to a certain util? I heard that's how it's done in the south...

    Joint trenching....love it love it love it...Locate one utility and mark for 3 and usually found by 60 cycle. Only have to worry about crossings and thats no biggie with a pipehorn.

    and yes bout all new subs do it where I work in the south.

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    Senior Member USIC1's Avatar
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    Default Re: Life expectancy of primary and secondary power???

    Thanks for the input...

    Thought others would be interested as well...

    Sometimes the not right types like to take an intermission from the human ping pong game to interact on issues of the mundane...

    Now, back to the game!!!opcornsmile:

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    Default Re: Life expectancy of primary and secondary power???

    Quote Originally Posted by USIC1 View Post
    Was curious if anyone has any RELATIVE knowledge of years of service (life expectancies) of buried electric cables!?!?!

    I know they are more frequently replaced throughout older neighborhoods then telco, and tv, and also wonder if the material used today allow for a greater lifespan...

    Wonder if its because of older concentrics and the deterioration of those outer bare ground strands, or even with the non-concentric that a tole is taken from heat and current (molecular flow) compromising the core over time deteriorating the metallic element or even the insulating content???

    Does a decision to replace ONLY come from random outages on older cable, or is there some form of inspection that calls for replacement prior to fault occurences???

    Do we have any brains around here that have delved into this technicality???


    I used to do this work, hi-potting cables and fault location.

    In general electrical equipment is to have a 30 year lifetime. The longest lasting cables are called pipe type. Here a heavy pipe, like a gas main pipe, is used as conduit. It is welded (each weld is x-rayed to insure quality) together and covered with a thick tar like coating in addition to sacrificial anodes for electrolysis control. The cable is pulled inside, the air vacuum pumped out and then filled with insulating oil. The trench around the pipe is filled with sand. Many of these have been in service since the 1930's. Fault location is interesting and locating these is like locating any buried pipe plus youo can 60 cycle them.

    Next is the old leaded cable type used in city manholes and conduits. These are mostly three phase primary cables and some secondary’s. What is important is that this predated the direct buried cables that started getting used in the suburbs in the 1960s as they influenced thinking.

    The city manhole and conduit system would have cable faults either in the manhole, where a simple splice was made, or in the duct run. In the duct run they just pulled out that run between the manholes and that section pulled in new cable.

    Having directly seen and head what I write next, well this is a case of the obvious not being seen. When a fault occurs on direct buried cable, around here commonly called URD for Underground Rural ( or Residential ) Distribution, the fault is dug up - cut out - and a splice is made. Unlike conduit cable the old run of cable is left and being old has a shorter life span left. Honest to God I explained this to my superiors and they still refused to believe it, they could not get the old conduit cable system out of their minds.

    Now for URD, there are many factors and installation method is a critical one. These cables were designed to be installed in layers if in a trench with other utilities. The electric on the bottom, phone above, etc. The electric would be backfilled with clean sand surrounding the electric cables.

    The first problem is that some companies went cheap and did not backfill with clean sand. They just backfilled with the excavation dirt complete with rocks, branches and twigs and many workers threw their lunch trash of bottles and cans into the trench. These got pressed against the cable and caused minor nicks and scratches. Now most people think that his lets in water and reduces the life of the cable, this is partially correct.

    In such cable there are five layers. A thin layer around the cable, the thickest layer of insulation, a thin layer of semi conducting material, a layer of neutral (neutral / ground wire external layer on the older cables) and then the final layer of jacket that is water proof.

    That thickest layer of insulation also is water proof so a nick in the jacket does not soak through to the conductors. The secret to the vulnerability is the layer of semi conduction material and the reason it is there.

    There is no perfect insulator and a small amount of electric flows through the insulation.
    The purpose of the semiconductor is to make the flow of electric from the conductor to the outside jacket equal. If the semiconductor is nicked then that will create a point of higher conductivity and the electrons will flow to that point. The long term effect of this unbalanced flow makes an electron path that eventual grows to where the insulation breaks down and you get a fault.

    Improper installation made for a higher failure rate that was not expected.

    Next is a problem that was not considered to be a problem, lightning. It was thought that direct buried cable would not be susceptible to lightning damage and in the early years this appeared to be true. Turned out that the wires going to the URD sections were overhead and they would get lightning strikes. The over voltage spike from the lightning strike would travel down into the URD cable. Even if the spike did not cause an immediate fault it caused weak points for form in the cable insulation which would become faults later.

    I did hi-pot tests and cable fault location for five years and then took a job in dispatching crews for a power company. When I first started and a storm was spotted coming in the daytime URD crews were switched to overhead equipped trucks, we kept on one URD crew on just in case. Within five years we started keeping URD crews in their trucks and soon after began moving overhead crews into URD trucks to cover all the UDR cable faults that occurred due to lightning.

    Lightning produced a cumulative damage effect that was not factored in and added to improper installation resulted in reduced cable life.

    Now for one last adverse afect, reflection spikes from cable faults. Every one has seen on television and movies the 60 cycle sine wave of electricity on an oscilloscope. Now imagine a fish tank filled with water and make a wave in it. The wave hits the end of the tank and the wave doubles or more in height and then rolls back down the tank as a smaller wave. Electricity does a similar thing when it hits the end of a conductor such as a breaker contact or where a fuse has blown. The voltage suddenly spikes and reflects back down the cable at the speed of light. This short spike, maybe a fraction of a cycle, causes weak points to occur the same as a lightning strike.

    As the cable gets older and there are more faults there are more reflective spikes further weakening the cable. Since the level of lightning damage and damage form improper installation were not considered there is higher than anticipated reflective spikes causing the cable life to again be shorter than anticipated.

    In my area all the factors above are in place resulting in URD electric primary being a candidate for replacement after 15 years of service.
    I find most URD primary installations needing replacement by 20 years. Do not consider the planned life engineered into the cable but consider the above factors. Look at how long they last in your area an by which company installed them.

    Every piece of URD primary will need to be replaced by a directional bore crew at some time. This for locators is both job security and a threat to job security.


    I find that these bore crews are pressured to bore closer to existing lines than is prudent. Very often the easement is small and there is little room for them to do anything else. This makes accurate locating critical on a directional bore job. Because these lines have been in the ground for at least a decade they share the easement with other lines that have been replaced from phone mains, phone services, CATV mains and services which again makes accurate marking difficult.

    In the future the problem will continue to get worse as the easement fills up with abandoned cables which will also read on the locating equipment.
    I understand that CATV lines have a relatively short life expectancy, maybe 5 to years. This started with getting the cheapest cable possible because CATV was not supposed to last beyond a few years, everyone thought satellite TV would make it completely obsolete by around 1995.

    Directional bore replacement of existing primary electric, and phone mains, will form a source of work for locators that is recession resistant. Even when new construction slows the existing lines must be kept working. The demand will be for not only better locating equipment but better locators with experience and top grade skills. Directional bore jobs are not for beginners or people with just a year or two experience.


    Any questions?

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    Default Re: Life expectancy of primary and secondary power???

    Quote Originally Posted by sling'n paint View Post
    Joint trenching....love it love it love it...Locate one utility and mark for 3 and usually found by 60 cycle. Only have to worry about crossings and thats no biggie with a pipehorn.

    and yes bout all new subs do it where I work in the south.
    I always hook up to each utility I am require to mark because in an older installation something may have been added. Hooking up to just one utility, or just using 60 cycle, can miss something.

    Even in new subdivisions just hooking up to one utility or just 60 cycling can go very wrong. In one subdivision phase towo was completed. The contractor ran the phone main up to the end of the road, about 10 houses and dead ended it for the phase three to connect to. The thing is the contractor put in the wrong size feeder, not enough pairs. They had to go back when phase three was starting up and trench in an additional new main just to feed phase three. Just hooking up to another utility could cause the new phone main to be unmarked.

    Unless marked a couple of times before, and recently, by connecting to all utilities I cannot recommend hooking up to just one utility and marking it all as joint buried.

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    Conservative Meanie ifinditunderground's Avatar
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    Default Re: Life expectancy of primary and secondary power???

    Quote Originally Posted by ProfessionalLocator View Post
    I used to do this work, hi-potting cables and fault location.

    In general electrical equipment is to have a 30 year lifetime. The longest lasting cables are called pipe type. Here a heavy pipe, like a gas main pipe, is used as conduit. It is welded (each weld is x-rayed to insure quality) together and covered with a thick tar like coating in addition to sacrificial anodes for electrolysis control. The cable is pulled inside, the air vacuum pumped out and then filled with insulating oil. The trench around the pipe is filled with sand. Many of these have been in service since the 1930's. Fault location is interesting and locating these is like locating any buried pipe plus youo can 60 cycle them.

    Next is the old leaded cable type used in city manholes and conduits. These are mostly three phase primary cables and some secondary’s. What is important is that this predated the direct buried cables that started getting used in the suburbs in the 1960s as they influenced thinking.

    The city manhole and conduit system would have cable faults either in the manhole, where a simple splice was made, or in the duct run. In the duct run they just pulled out that run between the manholes and that section pulled in new cable.

    Having directly seen and head what I write next, well this is a case of the obvious not being seen. When a fault occurs on direct buried cable, around here commonly called URD for Underground Rural ( or Residential ) Distribution, the fault is dug up - cut out - and a splice is made. Unlike conduit cable the old run of cable is left and being old has a shorter life span left. Honest to God I explained this to my superiors and they still refused to believe it, they could not get the old conduit cable system out of their minds.

    Now for URD, there are many factors and installation method is a critical one. These cables were designed to be installed in layers if in a trench with other utilities. The electric on the bottom, phone above, etc. The electric would be backfilled with clean sand surrounding the electric cables.

    The first problem is that some companies went cheap and did not backfill with clean sand. They just backfilled with the excavation dirt complete with rocks, branches and twigs and many workers threw their lunch trash of bottles and cans into the trench. These got pressed against the cable and caused minor nicks and scratches. Now most people think that his lets in water and reduces the life of the cable, this is partially correct.

    In such cable there are five layers. A thin layer around the cable, the thickest layer of insulation, a thin layer of semi conducting material, a layer of neutral (neutral / ground wire external layer on the older cables) and then the final layer of jacket that is water proof.

    That thickest layer of insulation also is water proof so a nick in the jacket does not soak through to the conductors. The secret to the vulnerability is the layer of semi conduction material and the reason it is there.

    There is no perfect insulator and a small amount of electric flows through the insulation.
    The purpose of the semiconductor is to make the flow of electric from the conductor to the outside jacket equal. If the semiconductor is nicked then that will create a point of higher conductivity and the electrons will flow to that point. The long term effect of this unbalanced flow makes an electron path that eventual grows to where the insulation breaks down and you get a fault.

    Improper installation made for a higher failure rate that was not expected.

    Next is a problem that was not considered to be a problem, lightning. It was thought that direct buried cable would not be susceptible to lightning damage and in the early years this appeared to be true. Turned out that the wires going to the URD sections were overhead and they would get lightning strikes. The over voltage spike from the lightning strike would travel down into the URD cable. Even if the spike did not cause an immediate fault it caused weak points for form in the cable insulation which would become faults later.

    I did hi-pot tests and cable fault location for five years and then took a job in dispatching crews for a power company. When I first started and a storm was spotted coming in the daytime URD crews were switched to overhead equipped trucks, we kept on one URD crew on just in case. Within five years we started keeping URD crews in their trucks and soon after began moving overhead crews into URD trucks to cover all the UDR cable faults that occurred due to lightning.

    Lightning produced a cumulative damage effect that was not factored in and added to improper installation resulted in reduced cable life.

    Now for one last adverse afect, reflection spikes from cable faults. Every one has seen on television and movies the 60 cycle sine wave of electricity on an oscilloscope. Now imagine a fish tank filled with water and make a wave in it. The wave hits the end of the tank and the wave doubles or more in height and then rolls back down the tank as a smaller wave. Electricity does a similar thing when it hits the end of a conductor such as a breaker contact or where a fuse has blown. The voltage suddenly spikes and reflects back down the cable at the speed of light. This short spike, maybe a fraction of a cycle, causes weak points to occur the same as a lightning strike.

    As the cable gets older and there are more faults there are more reflective spikes further weakening the cable. Since the level of lightning damage and damage form improper installation were not considered there is higher than anticipated reflective spikes causing the cable life to again be shorter than anticipated.

    In my area all the factors above are in place resulting in URD electric primary being a candidate for replacement after 15 years of service.
    I find most URD primary installations needing replacement by 20 years. Do not consider the planned life engineered into the cable but consider the above factors. Look at how long they last in your area an by which company installed them.

    Every piece of URD primary will need to be replaced by a directional bore crew at some time. This for locators is both job security and a threat to job security.


    I find that these bore crews are pressured to bore closer to existing lines than is prudent. Very often the easement is small and there is little room for them to do anything else. This makes accurate locating critical on a directional bore job. Because these lines have been in the ground for at least a decade they share the easement with other lines that have been replaced from phone mains, phone services, CATV mains and services which again makes accurate marking difficult.

    In the future the problem will continue to get worse as the easement fills up with abandoned cables which will also read on the locating equipment.
    I understand that CATV lines have a relatively short life expectancy, maybe 5 to years. This started with getting the cheapest cable possible because CATV was not supposed to last beyond a few years, everyone thought satellite TV would make it completely obsolete by around 1995.

    Directional bore replacement of existing primary electric, and phone mains, will form a source of work for locators that is recession resistant. Even when new construction slows the existing lines must be kept working. The demand will be for not only better locating equipment but better locators with experience and top grade skills. Directional bore jobs are not for beginners or people with just a year or two experience.


    Any questions?
    What a great post, I learned a great deal from it. Reminds me of a former member from NC that used to post and had extensive knowledge of power systems. I can't remember his name, any help? He was a volunteer Firefighter that also did tower work.
    There is a fine line between "Hobby" and "Mental Illness."
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    Default Re: Life expectancy of primary and secondary power???

    Quote Originally Posted by ProfessionalLocator View Post
    I always hook up to each utility I am require to mark because in an older installation something may have been added. Hooking up to just one utility, or just using 60 cycle, can miss something.

    Even in new subdivisions just hooking up to one utility or just 60 cycling can go very wrong. In one subdivision phase towo was completed. The contractor ran the phone main up to the end of the road, about 10 houses and dead ended it for the phase three to connect to. The thing is the contractor put in the wrong size feeder, not enough pairs. They had to go back when phase three was starting up and trench in an additional new main just to feed phase three. Just hooking up to another utility could cause the new phone main to be unmarked.

    Unless marked a couple of times before, and recently, by connecting to all utilities I cannot recommend hooking up to just one utility and marking it all as joint buried.
    You are correct on that aspect of joint trenching. I have a sub that is exactly what you described...originally they ran fitl fiber in the sub but decided they only need 100pr so they went 10' behind the joint trench and bored in the 100pr. So when I mark I always put a mark for the 100pr and then with the joint trench I put a mark for the drops that run in the joint and cross over.

    All this goes to knowing your area and keeping up with changes. As long as you keep up you know when 60 cycle will catch all and when you need to hook up.

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