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Thread: 3 wire transformer

  1. #1
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    3 wire transformer

    So i get a call out ... small explosion in a machine ... the transfomer went up in smoke ... no fuse protection ... no cicrcuit breaker ... the machine has been working for a few years ... and no changes have been made to the wiring (as it is from China)

    The part that still gets me ... 0-230-380

    The transfomer supplies the controls and the coolong fan ... L1 - 380 (white wire) ... controls and fan connected to 230 (yellow wire) ... L3 - 0 black wire ... then to confuse you ... things like the thermostat are connected on the 0 volt side ... but the n/o of the timer and temp controller are connected to the 230 volt side.

    I have figued it all out created a schematic diagram ... removed the transfomer ... changed the wiring ... connected a neutral from the 5 pin plug and it is working ... but still battling to get my head around the 0 v connected to L3 ... not something i would ever do or done in the past when designing and building electrical control panels.

    I have googled and found a ton of info on auto transfomers and how they work ... and used to save money.
    Comments are based on opinion...not always facts....that's why people use an alias.

  2. #2
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    So its 380/400v in and then 220/230v out ? If I understand you correctly. I have seen a few of these in panels. Few I can remember was from Germany some from Italy and some other ones was from the Netherlands so wont say its a China only thing. If I understand the reasoning behind this correctly its so that you only need to bring in 3 phases and earth as the machine/ panel makes its own “neutral” if you can call it that. So any neutral problems on the feed side wont make a problem for that machine. So no nasty 400v spikes trough the 230v components when you lose the neutral for some reason. Sort of like a isolating transformer.It also saves on the cost of the cables as the 230v components in these machines only draw a few amps so the same size neutral to the phase conductor is not needed. So you use 3 core cable with separate earth. This is my understanding and if I am wrong please correct me.

  3. #3
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    0 = L3 (380 VAC) and neutral
    230 = control wiring
    380 = L1 (380 VAC)

    No fuses ... no circuit breakers ... just one big bang and a pile of smoke.

    https://en.wikipedia.org/wiki/Autotransformer
    Comments are based on opinion...not always facts....that's why people use an alias.

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