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 17 replies
  • Subscribers 32 subscribers
  • Views 3278 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

Main switch short circuit capacity.

wessex
Some guidance please.

Three phase TN-S supply from a private 800 kVA transformer. Distribution via a 240mm2 4 core SWA approx 20m in length from a transformer mounted feed pillar and protected by 315A fuses. At the intake position 100A BS 1361 type II fuses are fitted. I was looking to install a REC 4 main switch down stream from which would be three phase distribution by 10kA rated MCB's. My question is about the suitability of the main switch and its short circuit capacity at it's point of installation with regard to prospective fault current at this point which will be greater than 16kA or do the BS 1361 afford adequate protection for the switch ? Your thoughts please.
Parents
  • Former Community Member
    0 Former Community Member
    The line up the middle of the graph is the prospective short circuit current line


    For the RMS values (which is principally what you are concerned with here) then start on the bottom axis at say 25kA, follow that up to the 100A fuse line - then turn left and continue until you hit the prospective line, then follow that down to the bottom axis and read off the cut of value (in kA RMS) - it should be around 5 or 6 kA


    For the peak values repeat the exercise starting at the vertical axis  and head right to the fuse line


    The much maligned fuse is actually an incredibly useful bit of kit when it comes to managing high fault levels, without having to engineer the Bismark


    Regards


    OMS


Reply
  • Former Community Member
    0 Former Community Member
    The line up the middle of the graph is the prospective short circuit current line


    For the RMS values (which is principally what you are concerned with here) then start on the bottom axis at say 25kA, follow that up to the 100A fuse line - then turn left and continue until you hit the prospective line, then follow that down to the bottom axis and read off the cut of value (in kA RMS) - it should be around 5 or 6 kA


    For the peak values repeat the exercise starting at the vertical axis  and head right to the fuse line


    The much maligned fuse is actually an incredibly useful bit of kit when it comes to managing high fault levels, without having to engineer the Bismark


    Regards


    OMS


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