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Isolating transformer help

MrJack96
fbfff694442d96ab55a4ca1cf11d99ce-huge-2f44b3c6-e82b-49a0-b1bd-1df87196400c.jpg36db8eb65df624d194c4f0d38bc9d37e-huge-858d560a-6a7b-4127-9383-db090315f918.jpg5829e0bca8ccbe2f8ca57ff4780fc9b2-huge-19d0edbf-ea01-407a-9fc4-6ac2c9c6ba51.jpgHi guys I have seen an isolating transformer feeding a single phase pump on site and am unsure if it should be isolated. I can see they have tied the 0v on the 110v side to earth just not the 240v Can anyone give me some advice. Here are some pictures. 


  • 0
    I presume it is a 110V pump with a  controller that needed a supply with a live and a neutral 110V apart,  rather than the centre earthed 55-0-55 that you often get given in the UK when you ask for 110V .

    As such, if that is the case,  it is a perfectly good way to do it, assuming the wattages are OK and it runs cool.


    Mike.
  • 0
    It’s 230v 0v but the 0v isn’t earthed
  • 0
    What I'd expect,

    1) the primary winding to be the 240V side, wired accross L and N. (N is also connected to E of course, but back at the source not there) If you put a meter between each end of the winding and ground in turn you would hope to see 240V on one and very little on the other..


    2) The secondary winding has 110V accross it and supplies the pump, and one side is tied to earth and we can call this the 110V pseudo-neutral, and the other side the 110V pseudo live. These have no direct connection to the incoming mains live and neutral - it is an isolation transformer after all, but If you put a meter between each end of the winding and ground in turn you would see 110V or so on one side and very little on the other. (and of course 110V across the 110v load as well...)



    If its not that, then if you could describe in more detail what is there that may help.



    PS staring at the photo, that transformer seems to have more than 2 windings- are the two top windings primaries and the lower ones isolated secondaries ?



    M.
  • 0
    The top one has 110v 0v that’s earthed and then 230-0v which has no continuity to earth 

    19796FB0-FB93-4150-9FF8-1A6FEBB63E9C.jpeg
  • 0
    The top are secondary
  • 0
    OK then, what is supplied by the isolated 240V ? (this is now sounding like a local IT island, rather as you would a shaver socket)

    (and is the pump on the isolated 110 that has ground at one side ?)

    M.
  • Former Community Member
    0 Former Community Member
    The usual reason for one leg of the 110 V winding being "tied" to earth is to make fault finding on those circuits easier......


    Regards


    BOD
  • 0
    MrJack96:

    The top one has 110v 0v that’s earthed and then 230-0v which has no continuity to earth 

    19796FB0-FB93-4150-9FF8-1A6FEBB63E9C.jpeg


    I am assuming that there are connections to the lower terminals, not very visible?  But there are some interesting voltage options available.

    looks like 220v 380v 420v 500v(?) and 550v  with a 20v label next to the Gn/Yl  I guess that allows for 240v 400v etc.  But 500v & 550v? I have never come across those. (In my time I've met some odd(?) voltages/frequencies even 112v DC for aircraft)

    Clive


  • 0
    500 volts is probably for use in America. Large or industrial buildings often have a three phase, 4 wire supply at 277/480 volts.

    Various countries use three phase, three wire systems with 500 or 550 volts between phases.


    It looks to me as though the transformer pictured is intended for mains input on the bottom terminals, with taps for numerous different voltages.


    I think that the output is intended to be from the top terminals, via two independent windings.


    I think that it has been wired other than as intended, with UK mains supply connected to the 240 volt output winding, and the 110 volt load connected to the 110 volt output winding.

    No reason this should not work, and it presumably DOES work. But not being used as intended. The capacity of the transformer MIGHT be reduced by connecting thus.

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