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Type D MCB 5 Second Tripping Current

Former Community Member
Former Community Member
In BS 7671 17th Edition A3 table 41.3 for type D MCBs gives a 5 second tripping current as 230 x 0.95 / (10In).


When cross referencing time current graphs for type D MCBs I do not get a value of 10In for a 5 second tripping time.


For example see ABB time current graph below giving a current of around 16In for a 5 second trip time.


What is the reason for the difference in values when comparing type D MCB time current charts and table 41.3 in BS 7671 17th Edition A3 for 5 second trip times?

3e6afca19b11a5e876e17f88e8258582-huge-type-d.png
f5deabd80c6b55bd27c69795fb1b7c94-huge-20190722_083103.jpg

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  • Former Community Member
    0 Former Community Member
    @mapj1‍ 


    I emailed ABB and they basically stated that the graph is taken from 60898-1. If what ABB are stating is correct it seems a bit odd that 60898-1 would allow a 5 second tripping current of 13In and BS7671 17th Edition A3 only allows 10In.


    "That Time/Current curve is the tripping curve as defined by the standard EN60898-1, and as such details the upper and lower limits allowable to conform to that standard"


    "The actual trip curve of the ABB MCB is of course much narrower and closer defined.     Specific curves are available and published in our freely downloadable software called Curves, link below :
    https://new.abb.com/low-voltage/launches/selectivity/tools-support/curves"






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  • Former Community Member
    0 Former Community Member
    @mapj1‍ 


    I emailed ABB and they basically stated that the graph is taken from 60898-1. If what ABB are stating is correct it seems a bit odd that 60898-1 would allow a 5 second tripping current of 13In and BS7671 17th Edition A3 only allows 10In.


    "That Time/Current curve is the tripping curve as defined by the standard EN60898-1, and as such details the upper and lower limits allowable to conform to that standard"


    "The actual trip curve of the ABB MCB is of course much narrower and closer defined.     Specific curves are available and published in our freely downloadable software called Curves, link below :
    https://new.abb.com/low-voltage/launches/selectivity/tools-support/curves"






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