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  • Energized wires

    I am looking for input on structural firefighting with energized electrical wires involved. If there are downed power lines in the vicinity or in contact with a structure, is it safe to enter? Another question, would it do any harm to knock the fire down using a master stream fog and possibly save exposures, or is there a major safety hazard associated with this? My thought is that if there is a fire in the front of a structure caused by downed wires, entry may be feasible from the rear and the structure may be saved.

  • #2
    It is never safe to enter a fire when there is down power lines that are energized NEVER EVER. It is ok to use UNMANED master streams as long as they are used to to control exposures as long as the power line insn't touching the exposure, there is no building more inportant than a human life. Remember the saying, Risk a lot to save a lot, risk a little to save little, risk NOTHING to save NOTHING
    NEVER EVER EVER go into a house that has an energized power line down on it NEVER case closed

    Stay Safe

    Comment


    • #3
      You can't go wrong with the "never" rule.

      However (for my real job I work at the power company), hang on for a long rambly answer......

      Energized lines are always looking for a path to ground. If they find it, they will arc and spark and make a nice light and sound show. If the system has proper protections in place, one of the following things SHOULD happen after ground is found:

      (a) A substation feeder or line breaker will trip (fraction of a second delay). It may attempt up to three automatic recloses within the span of a few minutes, so a dead line may not stay dead. Always treat wires as if they are hot unless you or a reliable person has seen a "visual open".

      (b) A field recloser in the line will trip (up to one second delay). As its name implies, it may also attempt to reclose a few times before locking open.

      (c) A poletop fuse will blow (up to several seconds delay). These cannot reclose, so once they are open you are more or less safe. These sometimes make a nice bang, so you know they popped.

      Depending on the location of the fault, and if the tolerances on the breakers and/or reclosers are not properly set, and if there is no poletop fuse in the line, the fault may be sustained, and you'll usually see and hear it.

      The voltages are different before and after the poletop "can" tranformers, and these voltages are directly related to the intensity of the light and sound show of a fault.

      The "high side" of the transformer on a feeder will probably be somewhere between 8,000 volts (8kV) and 34,000 volts (34kV). If they fault, you'll know! If they get anywhere near a grounding path, they'll arc the gap and take it. You'll know to stay back.

      The "low side" of the transformer will generally be no higher than 400 volts (usually less), depending on the requirements of what the line tap leads to (house, factory, shop, whatever). These can fault without being obvious unless you are paying attention and are relatively near it. A low side fault will not trip a feeder breaker or a recloser (this is what the poletop fuse is for if it is there).

      Back to where I originally wanted to go with this..... energized lines are always looking for a path to ground, and they will take the path if they can find it. If there are multiple paths, most (but usually not all) of the fault current will take the path of least resistance. As long as the line is faulting, you are "safe" because you are not personally the path of least resistance. If you get into a physical position where your body is an even marginally good partial path to ground, you're probably toast.

      If you really know your stuff, you could probably take the back door, as you put it, and knock the fire down. If you were 100% aware of the location of the lines and could somehow ensure that you would never be in a position to ground the fault, you'd probably make it. I am NOT saying this is a good idea, though.

      As far as master streams to protect exposures, it would depend on the voltage of the lines involved, the volume of water being moved, and the distance from the nozzle monitor to the energized source. For low level distribution voltage you can probably get away with it. Water conducts best when it has a high saline content (which is why the human body does it so well), but much less efficiently when it is of the municipal water main variety. At a distance, the water droplets are farther apart and don't make much of a good path. At higher voltages, the fault current is much more willing to jump air to get to ground. If the cumulative distances between the water droplets between the nozzle and the potential are less than how far the fault current would be willing to jump open air, you'll get a fault through your water stream, which obviously will ruin your day.

      A few rules of thumb for voltages to the lay person:

      The number of insulators between the wires and the pole structure increases as the voltages rise.

      1-2 insulator bells: up to 14kV, probably "safe"
      3-5 insulator bells: up to 69kV, getting into a danger
      more insulator bells: don't go there!

      It is not safe to guesstimate voltage by the pole construction material. Obviously steel poles or steel lattice structures will be high voltage, but you can get 230,000 volts (230kV) or more on wooden pole structures as well. They'll have a whole bunch of bell insulators, though!

      Higher voltages are always present when three power lines (or multiple sets of three) are present, and less so when only one power line is present. A main feeder path or transmission line will always have conductors in sets of three. A feeder distribution tap may have one, two, or three conductors. Conclusion: Three lines could be anything, but single lines generally are not going to be higher than about 34kV and usually not more than 14kV (which is still plenty dangerous anyway).

      Gosh this got way longer than I meant it to. And after all of that I still have to go back to plhansen84's response, which is best summed up as the "never" rule.

      "Never" is always the safest answer.
      You only have to be stupid once to be dead permanently
      - - - - - -
      I A C O J

      Comment


      • #4
        First off, I appreciate the long post. It had a lot of interesting information. This is more or less, what I was hoping to gain from this post. So thank you. Second, I was told that typically anything greater than about a 30-degree fog pattern would not allow the electricity to move up the line due to the space between the droplets. What type of wires is this is typical of? On a small commercial building or a residential structure, what size lines are going into the buildings? Also, once the line is broken between the street and the building, is the line attached to the house still going to hold charge and be a threat?

        Comment


        • #5
          Originally posted by RLFD14
          You can't go wrong with the "never" rule.

          However (for my real job I work at the power company), hang on for a long rambly answer......

          Energized lines are always looking for a path to ground. If they find it, they will arc and spark and make a nice light and sound show. If the system has proper protections in place, one of the following things SHOULD happen after ground is found:

          (a) A substation feeder or line breaker will trip (fraction of a second delay). It may attempt up to three automatic recloses within the span of a few minutes, so a dead line may not stay dead. Always treat wires as if they are hot unless you or a reliable person has seen a "visual open".

          (b) A field recloser in the line will trip (up to one second delay). As its name implies, it may also attempt to reclose a few times before locking open.

          (c) A poletop fuse will blow (up to several seconds delay). These cannot reclose, so once they are open you are more or less safe. These sometimes make a nice bang, so you know they popped.

          Depending on the location of the fault, and if the tolerances on the breakers and/or reclosers are not properly set, and if there is no poletop fuse in the line, the fault may be sustained, and you'll usually see and hear it.

          The voltages are different before and after the poletop "can" tranformers, and these voltages are directly related to the intensity of the light and sound show of a fault.

          The "high side" of the transformer on a feeder will probably be somewhere between 8,000 volts (8kV) and 34,000 volts (34kV). If they fault, you'll know! If they get anywhere near a grounding path, they'll arc the gap and take it. You'll know to stay back.

          The "low side" of the transformer will generally be no higher than 400 volts (usually less), depending on the requirements of what the line tap leads to (house, factory, shop, whatever). These can fault without being obvious unless you are paying attention and are relatively near it. A low side fault will not trip a feeder breaker or a recloser (this is what the poletop fuse is for if it is there).

          Back to where I originally wanted to go with this..... energized lines are always looking for a path to ground, and they will take the path if they can find it. If there are multiple paths, most (but usually not all) of the fault current will take the path of least resistance. As long as the line is faulting, you are "safe" because you are not personally the path of least resistance. If you get into a physical position where your body is an even marginally good partial path to ground, you're probably toast.

          If you really know your stuff, you could probably take the back door, as you put it, and knock the fire down. If you were 100% aware of the location of the lines and could somehow ensure that you would never be in a position to ground the fault, you'd probably make it. I am NOT saying this is a good idea, though.

          As far as master streams to protect exposures, it would depend on the voltage of the lines involved, the volume of water being moved, and the distance from the nozzle monitor to the energized source. For low level distribution voltage you can probably get away with it. Water conducts best when it has a high saline content (which is why the human body does it so well), but much less efficiently when it is of the municipal water main variety. At a distance, the water droplets are farther apart and don't make much of a good path. At higher voltages, the fault current is much more willing to jump air to get to ground. If the cumulative distances between the water droplets between the nozzle and the potential are less than how far the fault current would be willing to jump open air, you'll get a fault through your water stream, which obviously will ruin your day.

          A few rules of thumb for voltages to the lay person:

          The number of insulators between the wires and the pole structure increases as the voltages rise.

          1-2 insulator bells: up to 14kV, probably "safe"
          3-5 insulator bells: up to 69kV, getting into a danger
          more insulator bells: don't go there!

          It is not safe to guesstimate voltage by the pole construction material. Obviously steel poles or steel lattice structures will be high voltage, but you can get 230,000 volts (230kV) or more on wooden pole structures as well. They'll have a whole bunch of bell insulators, though!

          Higher voltages are always present when three power lines (or multiple sets of three) are present, and less so when only one power line is present. A main feeder path or transmission line will always have conductors in sets of three. A feeder distribution tap may have one, two, or three conductors. Conclusion: Three lines could be anything, but single lines generally are not going to be higher than about 34kV and usually not more than 14kV (which is still plenty dangerous anyway).

          Gosh this got way longer than I meant it to. And after all of that I still have to go back to plhansen84's response, which is best summed up as the "never" rule.

          "Never" is always the safest answer.
          Show off!
          PROUD, HONORED AND HUMBLED RECIPIENT OF THE PURPLE HYDRANT AWARD - 10/2007.

          Comment


          • #6
            RLFD14

            Very fascianting and informative post. Thank you.

            Comment


            • #7
              Originally posted by GeorgeWendtCFI


              Show off!
              LOL

              Sorry George. I love my job.
              You only have to be stupid once to be dead permanently
              - - - - - -
              I A C O J

              Comment


              • #8
                Originally posted by Firefig5813
                I was told that typically anything greater than about a 30-degree fog pattern would not allow the electricity to move up the line due to the space between the droplets. What type of wires is this is typical of? On a small commercial building or a residential structure, what size lines are going into the buildings?
                I think this is a relatively safe rule as long as you're not dealing with very high voltage lines. If the line in question is part of the service tap to nearby structures it should be OK as long as you're not ridiculously close to the conductor. Also, bear in mind for what it is worth that the conductors on the "high side" of the poletop transformer are generally not insulated (bare cable), while the conductors on the "low side" are almost always insulated (something that looks like VERY heavy duty extension cord). If the wire in question is part of a group of three wires with no taps to any customers nearby, then it is probably moderate to serious high voltage - keep your distance, the cables are never insulated. Regarding the voltages going into buildings, you shouldn't see anything greater than roughly 400 volts after the poletop transformer (usually less), but there are some rare exceptions. Also watch out for three-phase (three wires) electric service that goes down the pole to underground, as their voltages are not reduced until they eventually get to a pad-mount transformer somewhere else. The lesson here is that just because a line is routed down from the top of a pole it is not guaranteed to be reduced voltage.
                Also, once the line is broken between the street and the building, is the line attached to the house still going to hold charge and be a threat?
                Many residential and commercial buildings have automatic or manually-started backup generators installed, and you cannot depend on the presence of lights in/on the structure to make this obvious. If (and I emphasize IF) the transfer switch was installed properly, then the customer-side line laying on the ground should be dead whether the generator is running or not. Obviously in both the power company and the fire department, there are no guarantees. Also, I know some departments will re-energize a structure by plugging a department generator into a wall outlet of a de-energized building to provide a reverse feed (not a good idea), which means the place probably does not have its own generator, hence it has no transfer switch, hence the "dead" line laying on the ground outside is pretty much guaranteed to go hot again. You used the term "hold a charge", so I will clarify by saying that a building with its power service cut off and no generator will not act as a capacitor - there is no such thing as a residual charge in this context. If it is dead, it is dead pretty much right now. Hope this helps.
                Last edited by RLFD14; 05-16-2005, 06:27 PM.
                You only have to be stupid once to be dead permanently
                - - - - - -
                I A C O J

                Comment


                • #9
                  An additional comment on automatic reclosing....

                  Most (but not all) utilities have the ability to remotely enable or disable automatic reclosing functions on substation breakers. If you get into a situation where you don't necessarily want the line dead but there is a risk of a fault, or if there will be a time delay in killing the line, the utility can place the Feeder or Line in "non-auto". If it faults and trips, it will stay dead with no reclose attempts. This is the condition that most lineworkers operate in, so we're used to putting breakers on non-auto all day for crews on various jobs.

                  Example... today the department had a traffic accident with reports of a damaged pole. Nothing tripped in the field, but I had no way of knowing what the scene looked like or if a fault was imminent, so I figured out which Feeder was affected and put it on non-auto from the comfort of my chair before they even made the scene. Turns out it wasn't a big deal, but better safe than sorry.

                  In most cases as long as the utility has remote control over this function, putting a breaker in non-auto can be done very quickly (within seconds) depending on where the problem is at, compared with the time delay getting a bucket truck on the scene and physically disconnecting the power. It might be in everyone's interest to get together with their local utility and develop a plan for requesting lines be put on non-auto when when applicable and appropriate.
                  You only have to be stupid once to be dead permanently
                  - - - - - -
                  I A C O J

                  Comment


                  • #10
                    And let's not forget pathways to ground with resistance causing a voltage gradient across the ground and possibly not tripping a breaker or blowing a fuse link.

                    Comment


                    • #11
                      Damn, I need new glasses

                      Thought the topic was Energized Wives
                      Psychiatrists state 1 in 4 people has a mental illness.
                      Look at three of your friends, if they are ok, your it.

                      Comment


                      • #12
                        It all pretty much works for them, too.

                        Comment


                        • #13
                          I'm glad voltage gradients were brought up. For the uninformed, here's my understanding, which I post here at the risk of being corrected, Sister Mary Stigmata-style, by RLFD14:

                          When a hot wire touches the ground, it energizes the ground around it. Duh. But what I didn't learn right away is that the voltage decreases as you move away from the power source. Hence you have concentric circles of decreasing voltage centered around the hot wire. The importance of that is that anything that simultaneously contacts two or more areas of differing voltage will become the medium through which the juice equalizes, and the importance of that is that you don't walk away from hot lines, should you be in a position described above (which better be by accident, not choice). You hop with your feet together so that both of your hooves are in the same voltage at the same time.

                          Am I correct? Please don't use the ruler, Sister Mary!
                          “I am more than just a serious basketball fan. I am a life-long addict. I was addicted from birth, in fact, because I was born in Kentucky.”
                          ― Hunter S. Thompson

                          Comment


                          • #14
                            That's how they work.

                            Comment


                            • #15
                              First rate info LEWTFL, thanks!
                              ullrichk
                              a.k.a.
                              perfesser

                              a ship in a harbor is safe. . . but that's not what ships are for

                              Comment

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