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  • isolation transformer

    Good morning gentlemen!

    Whould someone be willing to explain how an isolation transformer protects an operator from elecrical shock? From reading the edm threads it was mentioned that it would prevent one from becoming part of an unintended circuit to ground,ouch! I just can't remember how it works. Thanks in advance and have a wonderful holiday season. May Santa fill your stockings with wonderful tools!
    hms50
    hms

  • #2
    Isolation transformer as the name implies isolates the load from the AC source. What this means is that the load is essentially floating (i.e. there no potential drop between the load and anything else including the ground). Touching one end of the load will not give you a shock even if you're standing in your bathtub full of water (declaimer, please don't try this).

    This is mandated by UL/CSA for many consumer goods.

    Many AC power tools get around this safety issue by using double insulated switch, which simply refers to a double pole single throw switch.

    One other application for isolation transformer is for electrical instruments, such as an oscilloscope, where the device has to make electrical contact with other electrical equipment. By floating the instrument, the chance of electrical shock is minimized.

    Albert

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    • #3
      Rotate has it right. With an isolation transformer there is no metallic conduction between the incomming power lines and the output of the isolation xformer. Its all magnetic coupling. Usually there is several thousand of volts worth of insulation between you and the incomming power. The only way to get shocked is to get across BOTH of the wires on the output side of the transformer. You can touch either side of the output and feel nothing, although a very sensitive meter may show voltage beteen the out put leads and the incoming power there is no current capability there. You can be measuring several volts and touch the out[ut line with your hand and be grounded and the voltage will drop to zero.

      What we call control transformers, power transformers, are USUALLY also isolation transformers. We mostly think of isolation transformers as putting out the same voltage as is put in (1:1 voltage ratio).

      If all the above just clearifies what you already know then good. If its new stuff, don't try to use he info- I have told enuff to be dangerous, and even 110 can make you assume room temerature as your dead body cools.

      Steve

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      • #4
        An isolation transformer electrically isolates both side of power from ground. In normal AC power supply one side is connected to ground. So if you become the connection between the other HOT side and any ground, current will flow. With the isolation transformer one side is not electrically connected to ground.

        Don Clement
        Running Springs, California
        http://www.clementfocuser.com

        Comment


        • #5
          SHucks I went back and re-read HMS50's post. He wishes EVERY ONE have stockings full of tools. I thought it was just those who answered the question who would get tools!

          Now we see why folks go on welfare- don't pay to work no mo'. Santa gonna give us ALL ben'fits.
          Hope Thruds are all shiney, and Alistairs hopes are granted.

          Steve
          even HMS50 gets an 5KW isolation xformer.


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          • #6
            All the above about an isolation transformer is well and good but it is not to be considered a complete, 100% prevention of a shock hazzard.

            To be shocked, you must complete the circuit; that is be connected to both sides of a voltage source. The transformer's secondary winding has two sides as all voltage sources do and if you connect one of these to ground, you loose all the shock prevention advantages of the transformer. Likewise, even if the secondary is not grounded, if you are foolish enough to come in contact with both sides of the secondary, you will most certainly get shocked just as if you came into contact with a hot wire of the shop wiring while also being in contact with a ground.

            Paul A.

            Make it fit.
            You can't win and there is a penalty for trying!

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            • #7
              Steve
              I have a picture of Santa using my chimney as a rest stop - this pretty well sums it all up. Rabbit turds, sticks, and if I am lucky...a lump of coal. I have been a baaaad boy raising holy hell with the "suits".

              Comment


              • #8
                Good morning gentlemen!

                Thanks for the re-fresher on isolation transformers. Some of what my poor, long-suffering teachers tried to make me learn has come back! It sems the use of an isolation transformer,like most safety techniques, is not 100% protection, but a prudent attempt to make a piece of equipment safer than it would be without it. As soon as the book on building an edm arrives the scavenger hunt will began. If finding the parts is not a problem, it seems to me this would be a great project. Having finished the T-slot compound slide from MLA, I've ordered the rear toolpost holder. That should be a "quicky" if my brother in law doesn't keep showing up with "serious" work for me to do.

                Thanks again,
                hms50

                P.S. Docsteve66,

                yes, now you knoe I'm a bleeding heart liberal!!!!!!!!!!!!!!!!!!!!!
                hms

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                • #9
                  I think most all of us are "bleeding heartss" in the snese that no one will suffer if we can alliviate their suffering. What gets me is when the "sufferer" retires at age 13 to loaf 24 hours a day and a working man has to work 4 of his 8 hours to support that loafer. then to cap it all off, at age 65-75 the worker is "given" less than the loafer has been getting (and will get).
                  Why , Oh Why, did daddy make me go to school, the teachers make me study so hard when, I had I been smarter, I could have retired in the second grade?

                  Steve

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                  • #10
                    Doc, I know what your saying,I've had a job since I was 14. My parents taught me to work for what I wanted, and I thank them for it. the older I get, the more I appreciate there guidance! In a few more years my working days will be over, (more shop time!). I look forward to that day, but I would'nt trade the life I've had for any "free" ride. Too many of friends born with silver spoons in their mouths traded them in for coke spoons!
                    Thanks again
                    hms50
                    hms

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                    • #11
                      You know! Thats another thing thats hard to comprehend! Those that loaf (or bum) can't find anything to do except take mind altering drugs, agitate, fuss ,grumble. Folks that have worked seem (in large part) to look forward to retirement so they can WORK at what they want to work at. Its especially true of those who had happy, or even just productive, work lives.

                      Comment


                      • #12
                        Steve

                        Hey, who are you calling an agitating grummbler anywho?


                        I was forced into early retirement because of my medical condition. I hate loafing around. I am going nuts. Bastards will not let me go back to work. I don't care if they think it is better for my health to just take it easy and recover. I hate it. I would rather be keel hauled by a kneeling bus.

                        Comment


                        • #13
                          Anyone building an edm will be using an isolation transformer within it already, as the secondary windings of the transformers will (should) have no conductive connection to the primary. Don't select for use any transformer with such a connection. Autotransformers are made this way, so are variacs. If you elect to use anything like this, then do use an isolation transformer as well. Certainly there is still risk of shock if you get body parts across the secondary plus and minus. Skin starts to pass enough juice to feel at around 30 volts, depending on the person, skin moisture, etc. Even a mild shock can be dangerous, if it results in a body part being spastically jerked out of the way of the electrodes, and into a cutting tool, or a corner of a doorway, or a friend's eyeball, or into the side of the drill press, which starts to fall over---- . Just a bit of info and a safety reminder here.
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                          • #14
                            darryl: I think this discussion of isolation xformers started several topics ago. OSO mentioned a EDM in HW that used 110v with no isolation Xformer at all. Done properly, the EDM tied the low side of 110V to the work piece, the high side to the electrode via some current limiting resistors. A very dangerous situation in the hands of a person lacking electrical knowledge, or a person who is even slightly careless. An isolation Xformer would have lessed the risks involved.
                            I take the time to explain be cause when you say "ANYONE" (i added the emphasis) "building an edm will be using an isolation transformer within it already, as the secondary windings of the transformers will (should) have no conductive connection to the primary. Don't select for use any transformer with such a connection" , have covered way too much territory. I know you firther explained and clarified but when the question is "what is an isolation transformer", you are providing confidence that is not warrented.

                            I once had to give a safety lecture on how to handle electricity. It was very short- make a grounding stick probe on one end alligator clip on the other end. alligator clip to a known ground, beat EVERY THING with the other end. If you see a spark, no matter how small, get rid of the spark." oneguy wanted to know if leather gloves would protect him, leather with tubber inside. My response was that if he had to ask the question he best stay away from electricity. But as OSO says, EDM is inherently dangerous (as are welders) so best treat them like yu would a rattler in bed with you- carefully move away and call for help.

                            "its what you KNOW that ain't so that gets you in trouble"

                            Steve

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                            • #15
                              Just for reference, linemen used leather gloves over rubber, for rough "hot" work so the rubber does not get cut. SWeat could leak enough current to kill, so any cut could be fatal.

                              Naturally the rubber glove portion was longer!

                              Electricians often use just the rubber for low voltage work, like meter hookups.

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