Q & A of the Day - Can I obtain back-up protection for this installation?

Question: I have just calculated a prospective short circuit current to be just over 16kA at the load end of a final circuit via Amtech. Obviously this can be protected against with an MCB, however the distribution board which houses the MCB is fed locally from a 80A fuse protected tap off box. The busbar upon which the tap off box is mounted is protected by a 800A MCCB.

In Amtech, cascade protection isn't available for the final circuit MCB as it's greyed out.

Do you know whether this is a glitch and that protection is available from the supply side devices, or is protection not available due to the slower disconnection time of the fuse?

Answer: This would seem to be a glitch. Depending upon the MCB, we can offer back-up protection from fuses to our MCBs. Please download our technical catalogue for MCBs and see chapter 10 for the relevant information - download by clicking on the link below (.PDF doc - 16.3MB):

http://library.abb.com/global/scot/scot209.nsf/veritydisplay/eb73f6036151160dc12575440038963a/$File/2CSC400002D0207.pdf

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