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OT: How strong is a power line? (Tree down in todat's storm)

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  • OT: How strong is a power line? (Tree down in todat's storm)

    About 3:00 this afternoon a fairly powerful thunderstorm rolled through. There were some pretty close lightning strikes followed quickly with thunder. Tibbs was not happy. Then the lights flickered several times, while I heard the "bong" sound of current in the power lines, and the power went out completely. When I looked out the window, I saw that a moderate-size tree had fallen next to the house, and it looked like it had landed on top of my car. I assumed it had taken out the power lines, so I called BGE and they said they would be out soon.


    The rain let up a bit and I was able to go outside, where I saw that the tree had been caught by the power lines and my cherry tree, and it had not struck the car. The crown of the tree was hanging over Warren Road and looked to be dangerous, so I called 911 on my cell phone. My land line phone was out. I got into my car and drove further up into the yard to clear the tree.


    BGE and the police arrived about 4:00 PM while Tibbs and I were sitting outside. They pretty quickly cut up the tree with a pole saw, and soon restored power. Here are pictures and some video clips:









    http://enginuitysystems.com/pix/hous..._Down_3456.AVI (17M)

    http://enginuitysystems.com/pix/hous..._Down_3457.AVI (17M)
    http://pauleschoen.com/pix/PM08_P76_P54.png
    Paul , P S Technology, Inc. and MrTibbs
    USA Maryland 21030

  • #2
    Paul, run - don't walk - to your nearest 7-11 and buy a lottery ticket!

    That was your power drop. It's usually two aluminum insulated wires wrapped around a steel stranded carrier/ground wire. It's probably 3/8 to 1/2 inch diameter, depending on the current capability of your drop (usually 100-200 amps).
    As you saw, it was strong enough. A few years back in a storm a tree brought my power drop down, but in my case it ripped the mast off the side of my house. Bent it to nearly 90 degrees. That mast was sch. 80 2" galvanized steel.

    -js
    There are no stupid questions. But there are lots of stupid answers. This is the internet.

    Location: SF Bay Area

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    • #3
      The answer to how strong..... is usually "A lot stronger than the tie point on your house".

      Standard procedure is for the line to pull the attachment off your house, and maybe yank out your service entrance cable. Then you call the powerco, and they tell you they are not coming, and in fact will not turn your power on until you have an electrician fix the service entrance cable (to the tune of a few hundred bucks, depending on what got shredded.)

      Your attachment is a goodie.
      1601

      Keep eye on ball.
      Hashim Khan

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      • #4
        I hadn't realized that the drop wire also had a steel cable messenger for the ground. I'd assumed it was simply more of the commonly used aluminium cable.

        I'm also surprised in that case that the tension of the tree didn't rip your drop right off from or right out through the wall of the house. That must have been a helluva load on it as it settled into place. In fact you may want to look in the basement and see if you're still sitting on the right spot of the foundations
        Chilliwack BC, Canada

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        • #5
          The problem with all-aluminum wires is they sag. And sag some more. And more. All from just the weight of the wire.

          My drop did rip the attachment from my eaves, bending the mast where it screwed into the meter case. I suspect a heavier tree would have ripped the meter and the service panel off my house too.

          -js
          There are no stupid questions. But there are lots of stupid answers. This is the internet.

          Location: SF Bay Area

          Comment


          • #6
            Originally posted by BCRider View Post
            I hadn't realized that the drop wire also had a steel cable messenger for the ground. I'd assumed it was simply more of the commonly used aluminium cable.
            ....
            A good deal of cable is "ACSR" as described above.... Aluminum Conductor Steel Reinforced. Basically any bare conductor cable is for overhead, and will be ACSR,
            1601

            Keep eye on ball.
            Hashim Khan

            Comment


            • #7
              As an old Journeyman Lineman I'm very surprised your mast held up; that's a pretty skoocum tree.

              Overhead house services tend to be Triplex cable with an ACSR (aluminium conductor steel-reinforced) neutral and for a 200 A entrance usually 1/0 aluminium conductors. From http://www.prioritywire.com/specs/Tr...ice%20Drop.pdf the breaking strength of 1/0 triplex is rated at 4380 lbs. Some triplex with 1/0 conductors had a reduced sized neutral (usually #2 neutral with 1/0 conductor) with a breaking strength of 2850 lbs.
              Location: Saskatoon, Saskatchewan, Canada

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              • #8
                Depending on if the line is a primary or secondary. Primary line usually have a steel core with seven aluminum wires wound around the steel wire. Secondary wires are or could be two covered aluminum wires with one bare wire. The primary lines are pretty tough, and made to withstand a lot of force. Secondary lines are usually designed to pull the connecting attachments from the building. Because nothing ever happens like it should, treat all power lines like they are there to KILL you and leave the area.
                _____________________________________________

                I would rather have tools that I never use, than not have a tool I need.
                Oregon Coast

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                • #9
                  Well the only conclusion I come to as to its strength is just strong enough, that's good!
                  We used to have twisted copper over here, worked fine but is being replaced with Ali at the taxpayers expense, when I asked what was happening to the copper they didn't want to answer, it's being sold as scrap and the utility companies seem to be pocketing the money, plus the taxpayer is also footing the £11 billion it's costing to install smart meters, and they add the cost to your bill, I see a pattern developing!, if I tried double scamming the consumer and the treasury I think I'd be in jail, many rules has the law.
                  Getting back to cable, ours is coaxial these days, Ali and steel, I've seen a tree leaning on a wire, fir or pine, must have been 50' so I'm guessing that stuff is fairly strong, the guy from the utility said they were installing carbon fibre reinforced as well, cheaper, never heard of the stuff before myself.
                  Mark

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                  • #10
                    I think the fallen tree is being held up a lot by the other tree.
                    So if you cut between the ground and the wire, unless supported, the load may increase if you cut it unsupported.

                    Comment


                    • #11
                      I think you are right. The cherry tree took a good bit of the force. Here are a few more pictures:









                      I was surprised how quickly and easily the work crew cleared this up, with a gas-powered pole saw. I thought they would need a bucket truck and perhaps a prop to support the tree near the wire. But first they cut the small limbs from the crown of the tree that were hanging over the road and caught in the cherry tree, then they cut the tree near the line, which took much of the weight off it. Then they cut it closer to the trunk, and it was on the ground. A few minutes more and they had the driveway clear. I have a bit of work to do, but they did a really good job. This is a locust tree, and it looks like it was still fairly healthy. I think it was just a strong gust of wind and soft ground where it didn't have very deep roots. I had been planning to take it down - now it's done - and it will provide some good firewood once it's cut up and seasoned. The cherry tree is not very healthy, and needs to be severely trimmed or possibly taken down. But I'm glad it was still there to save my car!
                      http://pauleschoen.com/pix/PM08_P76_P54.png
                      Paul , P S Technology, Inc. and MrTibbs
                      USA Maryland 21030

                      Comment


                      • #12
                        Early Saturday morning, about 6 AM, I was in bed half asleep, and I heard a crash-thud sound. I first thought it might be another accident on the road, but when I took a good look, I saw this:



                        Yes, same place where the tree came down, but this was just a branch from another tree. No apparent damage, but it was blocking half of Warren Road.





                        Upon closer look, it appears to be either locust or walnut, tangled up with grape vines and other weeds. It had rained rather heavily overnight and the weight of the wet leaves and vines probably pulled the whole mess down.



                        I probably could have handled the mess myself, but the main branch seemed pretty heavy, and I have had back problems. My gas chain saw has been sitting a long time and probably will need some work to get running. I have an electric saw and extension cord that should reach, and I have some heavy-duty loppers that can cut up to 1-1/2" branches. So I called 911 and started trimming off some of the smaller pieces. A policeman arrived and he was able to use the lopper to cut it down enough to pull it off the road and clear enough for me to get my car out. I wonder what will be the next bit of excitement here?
                        http://pauleschoen.com/pix/PM08_P76_P54.png
                        Paul , P S Technology, Inc. and MrTibbs
                        USA Maryland 21030

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                        • #13
                          you can call 911 for that? Probably get a citation around here

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                          • #14
                            Blocked roads are usually legitimate for a call, depending on the road. But in most cases, folks here would just haul it over to the side. If it is a whole tree, that might be different.

                            Concerning power line.... Neighbor had a biggish branch on her drop, clearly straining it. Branch maybe 6 inch size, down and leaning on the wires. Powerco gave a date 3 weeks later that they would deal with it.

                            Since she had the 3 wire spiral drop, but everything was still soaked from the rain I just put on the usual rubber gloves and leather ones over them (in case of pinholes or abrasions of the insulation), and we cleared it off with a come-along and saw. Safe enough, the gloves are good to 3kV at least.
                            1601

                            Keep eye on ball.
                            Hashim Khan

                            Comment


                            • #15
                              Call 911 for any situation that may involve an immediate danger to life. Trees across roads, partially blocking roads, and trees on power lines all qualify. Just a week ago we had a tree only partially blocking a country back road and a rather speedy driver hit the tree, flipped at least 1 1/2 times, and came to rest on the side of the car. Amazingly the driver was relatively unscathed as the car had something like a dozen airbags, all of which inflated...

                              Trees on power lines are a danger to life because too many people assume that the line is dead. They go to cut the tree up and wind up dead. Our fire department makes sure there is no immediate threat to civilian health and safety, and then we call the power company and wait for them to come chop up the tree. They can pull the gates on the appropriate poles to isolate that section of power line before cutting it. In large regional disasters we will sometimes cut the trees up after the power company has pulled the gates, but we will not do so before then.

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