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Help:- Isolation Transformer 240 - 110V

Discussion in 'Electronic Basics' started by SME, Jul 1, 2004.

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  1. SME

    SME Guest

    Hello Group.

    I need advice on isolation transformers!

    Are the yellow 240V-110V building site transformers isolated?
    I have purchased a 110V variac and wish to supply it with isolated
    power.
    This would be fed to tv / monitor / smps
    Oscilloscope will be attached etc etc for repair work and I am
    concerned with safety.

    TIA
    Steve.
     
  2. John Fields

    John Fields Guest

     
  3. burbeck

    burbeck Guest

    Hi Steve,
    your question raises a few points, firstly are you in the uk? i assume
    you are judging by your email NTL. i ask this as i cannot understand
    why you have purchased a 110 V variac, when the UK supply is 230 V.

    the yellow site transformers that you refere to are safety isolating,
    but they have a center tapped secondary (output) winding that is
    earthed, giving 55V from earth. which makes them not suitable for your
    application.

    the normal thing to do in a workshop enviorment is to have an earth
    free zone, a safety isolating transformer with no earth connection on
    the secondary. i refere you to the following

    www.hse.gov.uk/pubns/indg354.pdf
    www.hse.gov.uk/pubns/eis36.pdf

    RS and Farnell supply suitable transformers for this use, but account
    needs to be taken of the earth free zone recommendations.
    im sorry if this is a bit long winded but it is a complex subject
    regards
    bob
     
  4. burbeck

    burbeck Guest


    it is common cortesy to reply
     
  5. Don Kelly

    Don Kelly Guest

    You should be able to buy a 120/120V isolating transformer. 0.5 to 1KVA
    capacity should do you.

    I am puzzled by "Yellow 240/110V transformers" You often have transformers
    which are rated for 240V and center tapped- these are not isolation
    transformers.
     
  6. burbeck

    burbeck Guest

    hi don,
    the yellow transformers are a U.K thing, they are used to run 110V
    power tools, the mains voltage here is 240V. but on building sites it
    is required to use power tools that are 110V.
    see my first reply to the op for more info.
    regards
    bob
     
  7. Rich Grise

    Rich Grise Guest

    Sight unseen, I'd still bet money that they're autotransformers.
    They're way cheaper.

    And not isolated, if you're completely new to the field.

    Cheers!
    Rich
     
  8. burbeck

    burbeck Guest


    hi rich,
    the bet is lost, these transformers are 240V to 110V, with the
    secondary winding center tapped to earth, therebye giing 55 V max to
    earth. which is the reason that they are not suitable for the use that
    the original poster asked., see
    http://www.justgenerators.co.uk/pages/transformers.htm the ones that
    we are talking about are the yellow ones on this page. (110V)
    these units are a UK thing.
    i am not the original poster the thread got lost somewhere along the
    line
    regards
    bob
     
  9. Don Kelly

    Don Kelly Guest

    Thanks for the info- sorry I missed it before.
     
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