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MCCB settings help.

Former Community Member
Former Community Member
Hi, 


First time poster here. 


just looking for some advice from people cleverer than me. 


So my friends has asked me help him with a industrial job as i have done a bit in the past. We are looking to instal a panel board with 5 mccb. However when looking over the numbers a 160amp mccb gives a maximum value of 0.12 at lm @ 10 omhs. When doing a ze measurment he said he got 0.14 and calculated the r1r2 at 0.07 which gives a calculated zs of 0.21. However if we can change the setting to lm @ 6 omhs it gives is the 0.21 we need. However im not exactly sure what that lm @ x omhs setting actually is or does. Was just hoping someone  could tell me in lehmans terms what exactly it is.  


Hopefully the above makes sense. Thanks on advance for any help
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  • 0

    (C) Short Time pickup Current Setting (Im):



    • Short time protection is time-independent.

    • It is determines or sets the level of fault current at which the short-time trip delay countdown is actuated.

    • Short Time Pick up Value (Im) (multiplied by the ampere rating) sets the short circuit current level at which the circuit breaker will trip after the set time delay.

    • The short-time pickup (Isd) sets current level (below instantaneous trip level) at which circuit breaker will trip after the preset time delay.

    • Standard Practice for Setting:

    • No trip for a current below 80% of the short time setting

    • Trip for a current equal to 120% of the short time setting

    • The trip time is Less than 0.2 s for a short time protection with no time delay and equal to the value of the time delay tsd for a protection with time delay

    6 Adjustable Tripping Settings of a Circuit Breaker You MUST Understand | EEP (electrical-engineering-portal.com)


    Z.
Reply
  • 0

    (C) Short Time pickup Current Setting (Im):



    • Short time protection is time-independent.

    • It is determines or sets the level of fault current at which the short-time trip delay countdown is actuated.

    • Short Time Pick up Value (Im) (multiplied by the ampere rating) sets the short circuit current level at which the circuit breaker will trip after the set time delay.

    • The short-time pickup (Isd) sets current level (below instantaneous trip level) at which circuit breaker will trip after the preset time delay.

    • Standard Practice for Setting:

    • No trip for a current below 80% of the short time setting

    • Trip for a current equal to 120% of the short time setting

    • The trip time is Less than 0.2 s for a short time protection with no time delay and equal to the value of the time delay tsd for a protection with time delay

    6 Adjustable Tripping Settings of a Circuit Breaker You MUST Understand | EEP (electrical-engineering-portal.com)


    Z.
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