Lost Neutral

Discussion in 'Homework Help' started by Cerkit, Nov 14, 2012.

  1. Cerkit

    Thread Starter Active Member

    Jan 4, 2009
    275
    3
    Hi. Can someone please explain to me how the voltage in a phase will float to possibly much higher dangerous voltages if the neutral is lost. I am not sure how this comes about.
    I have read that if the loads over the three phases are unbalanced under connected neutral the unbalanced currents can run through the neutral, if the neutral is lost what happens to those unbalanced currents which result in the voltage to float, I think I have an intuitive feel of what is happening but can not put it in words.

    Thank you for any explanation.
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    Lets simplify and talk single phase, like in most homes in US. Transformer supply to the house is a 240V center tapped transformer (120v from each end to CT/240V end to end. Loads connected from one end to CT receive 120V. Loads connected to the two ends receive 240V. If the line connecting the return for a 120V load becomes disconnected between the transformer and the neutral buss bar, the current will then find a path through loads connected to the other side of the transformer. IF (a big if) the loads are balanced, both sides will see 120V (simple voltage divider with equal resistances). On the other hand, since the loads will in all probability NOT be balanced, the lighter load will experience higher voltage. Again, simple voltage divider theory. The Neutral line will normally carry any current that is the result of unbalanced loading.
     
    spark8217 likes this.
  3. Cerkit

    Thread Starter Active Member

    Jan 4, 2009
    275
    3
    Great response, thank you!!
     
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