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Amusing day at work.........

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  • Amusing day at work.........

    I spent all day blowing things up! Can't tell you what, because it's a legal matter, but....... can say some things.

    Job came in to figure out what happened to a piece of electrical equipment. The statement was that it "caused a fire"..... but it was apparent that because of the type damage, and the way it is constructed, that was unlikely. However, a suspicion isn't good enough, there has to be solid evidence of what probably happened..... facts that can be laid out without needing opinions etc.

    So I had to figure out if that could have been caused by any internal failure..... Basically I had to think up failures, cause them, and see if I could duplicate the damage.

    Had to keep the original piece of equipment exactly as it arrived, for evidence, but I had access to several similar ones that I could do whatever to. So first I tried various possible failures inside the equipment..... no dice, damage nothing the same as what was present.

    So then I had to see what external things could have happened.

    I finally came up with two ideas, both involving external faults that applied a higher voltage to a lower voltage wire.

    So there I am in the lab, deliberately cross-connecting the power line to things it shouldn't be connected to, and turning on the equipment to see what happens!

    I did end up getting a damage pattern that looked nearly identical to the actual one, so I figure I have it fairly well nailed down...... It's up to someone else now. As for the fire..... I figure it came first, and caused the power cross..... not the reverse, which I have a suspicion is what someone really wants to prove happened.

    Lots of sparks, close-up pictures, circles, arrows, but unfortunately, in this era of digital things, no 8 x 10 glossy photos with a note on the back of each one...........
    1601

    Keep eye on ball.
    Hashim Khan

  • #2
    I fully understand people cross connecting something and it causing a fire

    But how does a fire cause a cross connection??
    Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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    • #3
      Originally posted by Black_Moons
      I fully understand people cross connecting something and it causing a fire

      But how does a fire cause a cross connection??
      Burns through the insulation...?

      Comment


      • #4
        Originally posted by J Tiers
        Lots of sparks, close-up pictures, circles, arrows, but unfortunately, in this era of digital things, no 8 x 10 glossy photos with a note on the back of each one...........
        You can get any thing you want at .......!

        Dave

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        • #5
          Alices restaurant- can't remember if that includes Alice-
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

          Comment


          • #6
            ...Excepting Alice.

            Jerry, I get the opportunity where I work to do similar things, though usually not so spectacular.

            Most recently (yesterday) I spent a good portion of the day dismantling a solenoid coil in search of a wire break and the root cause. This was difficult because we wind and terminate the bobbin, assemble the frame and pole pieces, then overmold the whole thing with thermoset (Bakelite) plastic. I had to machine away most of the overmold and metal parts, leaving the bobbin and a thin film of overmold over the coil. I then carefully machined away one of the flanges on the end of the bobbin, exposing the coil windings. From this opening, I was able to pull out most of the wire, like a slinky, intact, while carefully watching for breaks, though I didn't expect to find any there. Rather, where the overmold touched the wire, I had to carefully tease each turn of wire free of the overmolded plastic. All this was done under the microscope, as the wire was hair fine 44 gage.

            Ultimately, I was able to find the actual break. Overmold material had forced its way between the magnet wire and flange of the bobbin and under the coil, pushing one turn of wire before it and eventually breaking the wire before freezing off with the two broken ends of the wire preserved, fossil fashion, in the thin semitransparent film of plastic. Once this was located, a simple microphotograph told the tale. Having the smoking gun, further simple detective work discovered a recent mold pressure adjustment made in the process that caused the problem.

            By the way, all of this, except the simple detective work, was done in my home shop.
            Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
            ~Practitioner of the Electromechanical Arts~

            Comment


            • #7
              If I had a mulligan on life the field of Forensic Engineering would get a real hard look. There is actually a Professional Forensic Society. They were originally oriented toward analysis of Boiler related problems but evolved into a broader view.
              Byron Boucher
              Burnet, TX

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              • #8
                But how does a fire cause a cross connection??
                You've discovered the "smart fire." At least that's we've nick-named it in Nuclear industry. The NRC came out with regulations concerning train separation and redundancy following incidents at a few stations. We were forced look at all wiring that supplied safety related components and develope procedures for manually failing these components in the safe position. In some cases, redundant circuits were addded or cables rerouted to prevent re-energization due to "Fire-Induced Hot Shorts."

                http://www.nrc.gov/reading-rm/doc-co...9/in99017.html

                Tom
                Tom - Spotsylvania, VA

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                • #9
                  Originally posted by becksmachine
                  You can get any thing you want at .......!

                  Dave
                  at Alices Restaurant
                  Exceptin' Alice

                  Comment


                  • #10
                    Originally posted by Black_Moons
                    I fully understand people cross connecting something and it causing a fire

                    But how does a fire cause a cross connection??

                    A fire that burns insulation and maybe causes nylon cable clamps to melt and drop the power wires onto unrelated wiring, or vice-versa.....when the insulation is melted or burned away.


                    I very much enjoy the "forensic" type work. Always a new thing to think about.
                    Last edited by J Tiers; 04-16-2011, 11:13 AM.
                    1601

                    Keep eye on ball.
                    Hashim Khan

                    Comment


                    • #11
                      Originally posted by Weston Bye
                      ...Excepting Alice.

                      Once this was located, a simple microphotograph told the tale. Having the smoking gun, further simple detective work discovered a recent mold pressure adjustment made in the process that caused the problem.
                      Here... certain key process parameters are locked. The setup-operator I have is permitted to adjust certain things. If those don't solve the problem I am to be contacted IMMEDIATELY. Everything is documented under the threat of severe pain and or firing.

                      98% of the so-called experienced techs and setups I interview tell you to solve under-fill or "short shots" with more pressure.

                      That is wrong. That is how you solve an "under-pack."

                      It takes an expert (and I am such an expert) to tell if the part is not filled out (lack of material) or not packing the mold correctly (lack of pressure.

                      My technique for troubleshooting involves moving the fill/pack transfer setpoint and watching the graph on the screen.


                      Thing is companies do NOT want someone who can actually troubleshoot they want someone who can push buttons and make visually correct parts. I've had interviews where they name a defect.. I outlined my troubleshooting process... and they told me "in the time it took you to figure all that out you made a dozen bad parts."

                      On the other hand if you simply turn the pressure up... you've now got molded in stress or insert failure (like Weston mentioned) or dimensional inaccuracy. So I may have made a dozen bad parts but at least I am 250% sure that I have solved the problem without causing two more.
                      This product has been determined by the state of California to cause permanent irreversible death. This statement may or may not be recognized as valid by all states.
                      Heirs of an old war/that's what we've become Inheriting troubles I'm mentally numb
                      Plastic Operators Dot Com

                      Comment


                      • #12
                        I have seen electrical boxes explode like a bomb.

                        My first experience was when I was working on a 480 volt 250 amp electrical box. The electrical box had a 2" hole in the top where an electrical knock out needed to be put to plug the hole. I measured the hole and returned with a knockout plug. The maintenance paid a pair of plyers on the ledge above the box while I was gone. All I had to do was put the plug over the hole and tap it with a hammer and I was finished. 2 large air compressors were running only a few feet away and everything was vibrating. As I was about to place the plug over the hole I was something fall then BOOM there was a big explosion brighter than an arc welder. The electrical box blew apart and both air compressors stopped running. Later I found the handles of a pair of plyers welded across the 480 volt terminals of that box. The maintance mans plywers fell directly into that 2" hole I was about to plug up.

                        I had an electrican install something to an exist box he drilled a hole in the top with a hole saw the slug fell on top of a 60 amp motor starter directly across the 480 volt terminals. Later when he turned on the voltage it blew the box apart like a bomb. The metal door was bent into a dish shape and the box was bent all out of shape.

                        Once I had an old dirty contactor explode because it was old and dirty. Very old machine lots of dirt and dust collected inside until it conducted electricity the whole motor starter blew up. There was pieces all over the place about 60 pieces and was burned black as charcoal.

                        Stuff like that is a CSI investigation after it happens to figure out what caused it.

                        Comment


                        • #13
                          Originally posted by Liger Zero
                          Here... certain key process parameters are locked........ I have solved the problem without causing two more.
                          Just so. In this case, the press runs two very similar but not identical products. The press was adjusted (by a manager) to solve a problem with the other product, and then later the molds were changed to run this product. Dead coils started showing up. Now the manager will have to establish two separate sets of parameters. I'm surprised that they have gone so many years using the same settings for both products. Something else has changed.
                          Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                          ~Practitioner of the Electromechanical Arts~

                          Comment


                          • #14
                            Originally posted by Weston Bye
                            Just so. In this case, the press runs two very similar but not identical products. The press was adjusted (by a manager) to solve a problem with the other product, and then later the molds were changed to run this product. Dead coils started showing up. Now the manager will have to establish two separate sets of parameters. I'm surprised that they have gone so many years using the same settings for both products. Something else has changed.
                            Either the material is slightly different or there is a wear in the machine. Check the screw tip/NRV and the end of the barrel.

                            (slaps $5 on table)
                            This product has been determined by the state of California to cause permanent irreversible death. This statement may or may not be recognized as valid by all states.
                            Heirs of an old war/that's what we've become Inheriting troubles I'm mentally numb
                            Plastic Operators Dot Com

                            Comment


                            • #15
                              Interesting read. Now, STAY THE HELL AWAY FROM MY PLACE!
                              - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
                              Thank you to our families of soldiers, many of whom have given so much more then the rest of us for the Freedom we enjoy.

                              It is true, there is nothing free about freedom, don't be so quick to give it away.

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