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ABB MCCB and 5 seconds disconnection.

Handyosprey
Hi all,

Looking for a bit of clarification on disconnection times here. I have information on an ABB Mccb that has been listed as failing on maz zs.

The max zs referenced for the unit is 0.07 ( 250a TMD TP set at maximum) the measured zs is 0.08, however, the max Zs is listed for 0.4 and 5 seconds.

Looking at the time current curve on the mccb once you hit 3.5.times 250a you are in the thermal tripping zone of the mccb. Using the curves software from ABB it indicates a 5 second disconnection can be achieved with 1.66ka.


How do I work this out? is the MaxZs listed as the same for both disconnection times because the only way to ensure a 5sec disconnection is to have an instantaneous trip?
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    It's an installation already in service and this is from a EICR. The install is around the 5 year old mark.

    Yes it has been measured as 0.08 Zs with a multifunction test unit.

    I cannot comment on the length of run.


    I seem to be getting issues of this nature across a lot of buildings on site. Baring in mind the majority of buildings are no more than 6 years old. It may be one to refer back to the contractors responsible. Sadly, the o+m info is missing any design calculations to enable a cross ref of what was expected.


    Am I correct in assuming that if the fault current was 8xIn the operating time would be anything between 0.7 to nearly 11 seconds ?

     

    Thanks all, for helping clarifying this for me. It's a bit easier to understand it with a few more opinions.



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  • 0
    It's an installation already in service and this is from a EICR. The install is around the 5 year old mark.

    Yes it has been measured as 0.08 Zs with a multifunction test unit.

    I cannot comment on the length of run.


    I seem to be getting issues of this nature across a lot of buildings on site. Baring in mind the majority of buildings are no more than 6 years old. It may be one to refer back to the contractors responsible. Sadly, the o+m info is missing any design calculations to enable a cross ref of what was expected.


    Am I correct in assuming that if the fault current was 8xIn the operating time would be anything between 0.7 to nearly 11 seconds ?

     

    Thanks all, for helping clarifying this for me. It's a bit easier to understand it with a few more opinions.



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