Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 15 replies
  • Subscribers 27 subscribers
  • Views 3918 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

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?
Parents
  • 0
    mapj1:

    (For example This dataasheet from Megger  suggests an accuracy on lop tests of  5% of reading +/- 5 counts in the least significant digit.

    So if the reading on the display was 0.080  then the real value to generate that could lie  anywhere between 0.071 to 0.089   (5% is 4 in the last place plus another 5 counts)


    This is odd! Would that be the case with an analogue meter?


    The Megger MFT's minimum value for EFLI is 0.01Ω so if the reading is anything up to 0.06Ω, it could be zero. Or you go to a TT installation where the EFLI is 100Ω and it could be anywhere between 90Ω and 110Ω. It's that last digit which troubles me. If the machine has measured to an accuracy of +/- 5% (much worse than a simple ruler!) why can it not express the value accurately?


Reply
  • 0
    mapj1:

    (For example This dataasheet from Megger  suggests an accuracy on lop tests of  5% of reading +/- 5 counts in the least significant digit.

    So if the reading on the display was 0.080  then the real value to generate that could lie  anywhere between 0.071 to 0.089   (5% is 4 in the last place plus another 5 counts)


    This is odd! Would that be the case with an analogue meter?


    The Megger MFT's minimum value for EFLI is 0.01Ω so if the reading is anything up to 0.06Ω, it could be zero. Or you go to a TT installation where the EFLI is 100Ω and it could be anywhere between 90Ω and 110Ω. It's that last digit which troubles me. If the machine has measured to an accuracy of +/- 5% (much worse than a simple ruler!) why can it not express the value accurately?


Children
No Data

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines