Breaker and overload selection

Discussion in 'General Electronics Chat' started by jiugo.llamas, Nov 27, 2007.

  1. jiugo.llamas

    Thread Starter Member

    Nov 23, 2007
    10
    0
    Hi everyone, I would liketo know if there is any formula which I can use for the breaker and overload of a motor starter selection based on the motor´s hp´s or power, how can I select the right protections?????

    Best regards

    Hugo
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    One would also need to know the voltage.
     
  3. jiugo.llamas

    Thread Starter Member

    Nov 23, 2007
    10
    0
    The voltage would be 480V......
     
  4. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    I=P/E:) as simple as that!

    Start-up current may be as much as six times run current.
     
  5. haditya

    Senior Member

    Jan 19, 2004
    220
    0
    and start up currents fall quickly..
    so a delay relay should probably help
     
  6. gerty

    AAC Fanatic!

    Aug 30, 2007
    1,153
    304
    Chances are pretty good that your calculation will fall between the available fuse size (eg 4.5 amps) . You'll need to go to the higher size and probably a time delay or slo-blo fuse. A time delay will allow the higher startup current
    to pass for a short time, but will blow if the current remains high..
     
  7. jiugo.llamas

    Thread Starter Member

    Nov 23, 2007
    10
    0
    What about the overload relay?? Is there any specific rule??
     
  8. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Different rules for different classes. Which class do you require?
     
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