Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Successive Circuit Breakers

  1. Jun 10, 2009 #1
    In a normal power distribution network there are successive circuit breakers each responsible fore the circuit that lies below them.

    Now suppose i assume that there is a short circuit in my house then shouldn't the circuit breaker that lies above the MCB in my house, maybe an ACB or MCCB in one of the power distribution boards trip, and if we go higher then shouldn't the highest level circuit breaker trip, before any of the successive circuit breakers trip??

    I know that my thinking is wrong, because in that case an entire city will lose electricity even when one of its residents has a circuit trip in their house. Can someone please correct my logic.
  2. jcsd
  3. Jun 10, 2009 #2
    I don't know the right answer...
    But maybe the circuit breaker for your house is rated at 30 amps while the one at the facility rated for... more than 30 amps?

    So the moment you go into 31 amps your house shuts down but you can theoratically get more than that?
  4. Jun 10, 2009 #3


    User Avatar

    Staff: Mentor

    Your post is confusing because you didn't define your acronyms, and because you seem to state a correct thing (the lower circuit breakers will pop first), and then say that your thinking is wrong. Could you please clarify both of those issues? Thanks.
  5. Jun 10, 2009 #4
    I apologize my vagueness.

    All i am asking is that there are successive circuit breakers in a circuit. Some which are closer to the Power Source end and some that are closer to the earth end.

    Now suppose a circuit breaker which is closer to the earth end (like the one in my house) is supposed to trip, shouldn't the circuit breaker that comes at a higher level (like the one at the power station) also trip(before my house circuit breaker). The logic being that since excess current which is wanting to flow at a lower level should also result in excess current flowing through at a higher level.

    (Level here refers to the position of the circuit breaker in the power distribution chain.)

    And this should result in tripping of a circuit at the power station before there is tripping at my house.
  6. Jun 10, 2009 #5


    User Avatar

    Staff: Mentor

    A power station wouldn't even notice the excess current flowing in your house. It can handle far more power flow than your house panel can.
  7. Jun 17, 2009 #6
    Please refer to selectivity, coordination and discrimination term of power system protection.
  8. Jun 17, 2009 #7
    The breakers are all in series. The lowest-rated breaker will flip (except if there are issues of breaker speed--but typically lower-rated breakers are also faster, anyway). The distance between breakers and their order in the series circuit do not affect which breaker opens (assuming there are no other current paths than the series path). the only reason there are multiple breakers in an otherwise series circuit, is to protect from unintentional shorts at different points along the line.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook