Transformer GND connection

Discussion in 'General Electronics Chat' started by Rubi, Jun 23, 2010.

  1. Rubi

    Thread Starter New Member

    Jun 13, 2010
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    I have a transformer from 110v to 24v with ground isolation, my question is if I can connect both grounds, from primary and secondary side. I need to know if this is no going to damage the transformer. Please reply ASAP!
     
  2. someonesdad

    Senior Member

    Jul 7, 2009
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    As is virtually always needed, post a schematic of what you're planning on doing -- it's much clearer than words...
     
  3. retched

    AAC Fanatic!

    Dec 5, 2009
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    Are you asking if you can connect the primary and secondary grounds together?

    If so, the answer is no. And why would you want to? You lose isolation.
    A schematic would clear things up, as someonesdad has said.
     
  4. Rubi

    Thread Starter New Member

    Jun 13, 2010
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    yes, retched this is what I meant. The issue is that I have an application circuit were I do not have a gnd/neutral present and a need to supply voltage to control it. I thought that probably connecting gnd/neutral of primary and secondary I can supply it. Hope this schematic explains a little bit.
     
  5. retched

    AAC Fanatic!

    Dec 5, 2009
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    Umm, no, that will not work.

    Do you have a transformer with only one wire on the secondary?

    The way it is shown, it will not operate. If you tie it to the other side, you will have 120v on the 24v side. so that wont work either.
     
  6. Rubi

    Thread Starter New Member

    Jun 13, 2010
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    no, the secondary has two wires but I have access to one wire only. I was just wondering that probably I can connect the primary and secondary gnd to have the loop I need, but it's not possible. Thank you so much, I have to keep searching another solution.:(:confused:
     
  7. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    I'd cross check with your manufacturer docs, but if you only have one lead on the secondary, you may have an autotransformer. You can do a continuity check to see if your one lead is connected back to the primary side.

    Connecting both primary and secondary to a ground common does not negate isolation (excepting above). It only adds a common reference point.
     
  8. Ghar

    Active Member

    Mar 8, 2010
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    I believe this is a safety requirement as well.
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    As long as we are talking ground, and not neutral. Ground should not be involved with the high voltage side (Hot or Neutral) of the transformer in any way.
     
  10. retched

    AAC Fanatic!

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    He is talking neutral.

    He only has ACCESS to one of the two wires off of the primary.

    So it has 2 wires, he just cant access the second.
     
  11. Ghar

    Active Member

    Mar 8, 2010
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    I agree, though let's get more specific - as I understand it the idea is that primary hot and neutral are both isolated from the chassis and ground while the ground is connected to the secondary neutral and chassis.
     
  12. timrobbins

    Active Member

    Aug 29, 2009
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    Rubi,

    Your comment is still unclear - "The issue is that I have an application circuit were I do not have a gnd/neutral present and a need to supply voltage to control it. I thought that probably connecting gnd/neutral of primary and secondary I can supply it."

    Do you access to the 'unconnected' output of the 24VAC winding?

    You have not shown a mains earth anywhere. Is there one present. If not then is the transformer and the application suitable for an unearthed product - do you know or are you guessing?

    Does your output need to be SELV rated?

    Ciao, Tim
     
  13. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    Yes, you are correct. Only the source is grounded, so your primary side, being a load for it's source, is not grounded. Your secondary, being a new source, is grounded.

    Neutrals only occur in 3 or more wire systems (not including grounds). Neutrals are only bonded to earth at thier source, with a code spec'd wire. The rest of the system is 'bonded' to ground. The 'neutral' in a 2 wire system is more apt identified as the 'identified' conductor.
     
    Last edited: Jun 26, 2010
  14. retched

    AAC Fanatic!

    Dec 5, 2009
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    Common would have been a better term to use. Even though I used Neutral. :oops:
     
  15. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    Continuity check the transformer including all wires and the case!

    Some transformers have been designed so that bolting the transformer into a grounded chassis makes a necessary electrical connection.

    Retched could be right; It is possible this is an autotransformer which will be easy to find out if there is continuity between the transformer output and input windings.

    Chances of a reverse wired outlet being used make electrical connection to neutral or hot side of the primary the wrong way to go.
     
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