MCB Switching off curve

Discussion in 'Electrics UK' started by chris911sc, 30 May 2005.

This topic originated from the How to page called Miniature circuit breakers (MCBs).

  1. chris911sc

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    Could somebody explain to me the difference between MCB switching off curves A, B & C?
    Thanks
     
  2. plugwash

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    afaict there is no type A

    basically a mcb has two parts

    the thermal trip is the same between a B a C and a D of the same rating and deals with relatively small but sustained overloads.

    the magnetic trip is designed to take out short cuircuits and it either trips or it doesn't. If the magnitic trip point is hit the breaker will trip extremely fast (0.1 sec is the standard iirc but some manufacturers claim even faster). The type of the breaker determines how many times the rated current is needed to take out the magnetic trip

    B is 3-5 times C is 5-10 times and D is 10-20 times.

    A lower fast trip point makes cuircuit design to meet earth fault loop requirements easier but can cause nusense tripping with some loads (b6 breakers on lighting cuircuits are well known for this issue).
     
  3. ban-all-sheds

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  4. Senarathne

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    What are the advantages and disadvantages of minature circuit breakers?
     
  5. JohnD

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    Compared to a chocolate cake, an MCB doesn't taste so good (disadvantage) but is better at cutting electrical overloads or short circuits (advantage)
     
  6. securespark

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    I find victoria sponge better at cutting overloads than a choccy cake...must be the jam...
     
  7. ban-all-sheds

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    Surely currant buns are the best for that purpose?
     
  8. RF Lighting

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    shouldn't that be a current bun? ;)
     
  9. TheGaffersSon

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    That's a shocking joke :LOL:

    I'll just get me' coat...
     
  10. ban-all-sheds

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    No - it's a homophonic pun.
     
  11. JohnD

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    homophonic bun, you mean.
     
  12. RF Lighting

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    Sorry I don't know what that word means.
     
  13. JohnD

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    A pun is a humerous wordplay with words that sound the same.

    "Homophonic" means sounds the same.
     
  14. ban-all-sheds

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    But are spelled differently.

    Can also be homographic - same spelling, different meanings, e.g. "Being in politics is just like playing golf: you are trapped in one bad lie after another."
     

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