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Thread: Q about isolation transformers.

  1. #1

    Q about isolation transformers.

    So I have always heard from every pro that you should use an isolation transformer to be safe when working on AC powered electronics. I understand what it does etc. Recently, I had someone tell me, save your money and just lift the ground bu using a wall plug adapter that converts the 3 prong to a 2 prong. I know it would work but I also know there is a reason no one does it that way. It would certainly be way cheaper and easier. Either way you are floating the earth ground yes? What is it that makes the isolation transformer safer? I know there must be a reason.

  2. #2
    As far as I know, power distribution networks use only three wires for each phase and the earth as the return. So your neutral wire is actually the earth of the nearest distribution transformer. The safety earth in your house is used as a low impedance return path to earth for things like metal cases or sensitive equipment, and should always be separate from the neutral.
    So as you are almost always "referenced" to earth, when you touch the live wire you are actually a lower impedance path to earth (than the neutral) and (some) current will go through you. This is why in industrial applications you are always required to wear isolation footwear, gloves or there are rubber mats under power distribution panels.
    What an isolation transformer does is, as the name implies, isolates the secondary side from the earth. So for a return path to be established through your body, you actually have to touch both wires simultaneously, which is unlikely.

  3. #3
    I think your question has been answer here in great detail, do you want to know anything else about isolation transformers?

  4. #4
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    Playing with 320v is no joke and if accidentally one touches it is lethal. One other reason for disconnecting the earth ground is for the purpose not to provide a return path to the scope when testing an smps, otherwise the scope can be burnt. Some form of isolation is always good to have and as explained by Bogdan and gives peace of mind during testing out of an off line smps. One thing you could do is to have 2 step down transformers wired back to back (EX. 220v in 12v out) connecting the 12v side with each other and thus having an isolated 220v output. The current will be limited due to the high inductance involved in both transformers but it will suffice until you get things going.

    I hope that helps.

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