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Discuss Voltage test on 110 transformer in the Periodic Inspection Reporting & Certification area at

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  1. Jabbajaws

    Jabbajaws Electrician's Arms

    Hi All,

    I did a voltage test on the output side of a 110 transformer, the other day, due to a 110 SDS drill that kept cutting out. It turned out to be a loose connection in the drill, but l was somewhat confused by the voltage readings l was getting from the transformer itself.

    L - N = 110V
    L - E = 110V
    N - E = 90V

    During training l was taught that there should be no voltage between Neutral + Earth when taking a voltage reading.

    Is this normal for 110 transformers or is there a problem?
    Not very experienced with transformers, so any input much appreciated. Thanks.
  2. i=p/u

    i=p/u Electrician's Arms

    i thought you should be getting 55v to earth, showws how much i know
  3. telectrix

    telectrix Scouser and Proud of It Respected Member

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    you should get 55V L/E and N/E. ( the N is not actually N ) it's really L1 and L2. the centre of the secondary TX winding is connected to the supply earth, so you should have 55-0-55.
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  4. Archy Styrigg

    Archy Styrigg Forum Mentor

    Your typical Yellow tranny has a 110V 2ndary winding centre tapped to earth.
    So, as our i=p/u says, +/-55v to earth. They don't have neutral as such.
    I'm confused by your readings. Sould be getting 110 across Line pins and 55 bot lives to earth.

    Either the trannies knackered or you're measuring incorrectly.
  5. Jabbajaws

    Jabbajaws Electrician's Arms

    Thanks Archy. It was only a quick test with my voltage indicator. I havent used my 17th edition meter on it for an accurate reading but l will do as soon as l get chance. Thanks.
  6. Engineer54

    Engineer54 Guest

    You should actually be using a pukka voltage tester, for your ''Accurate'' voltage readings, rather than your 17th MFT... Voltage indicator type testers that show you the voltage within an indicated band range, don't cut it these days... Is this the type of volt meter you was using??

    What you should be seeing is ....

    L1 - L2 = 110V
    L1 - E = 55V
    L2 - E = 55V
    Last edited by a moderator: Feb 19, 2012
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