Interrupting Rating of a Fuse

[FaradayFF]

Hi,

I've got a fuse located upstream that protects a pad-mount transformer; is the short circuit interrupting rating of the fuse as listed in the catalog the maximum fault current the fuse is rated for on the primary of the transformer(at the power fuse location)? In other words, the fuse must be rated to interrupt the maximum anticipated fault on the primary of the transformer.

Thank you,
EE

 

[bwat]

Generally speaking, any ocpd needs to have an interrupt rating that is at least as high as the available short circuit current at the point of the ocpd’s connection. So you need to look at the available SCC at the point where you are putting the fuse. What you end up feeding from that fuse is typically irrelevant because if there was a bolted fault directly on the load side of the fuse, the fuse would theoretically see the entire available SCC, so it needs to be rated for that.

Things can get a little more complicated with series ratings, current limiting devices, contribution of SCC from loads like motors, but the general concept still holds.

 

[FaradayFF]

Thanks, bwat.