Recently we had an issue with replacing a european fuse block and fuses with a North American style (Bussman Class J 600V 60A 3PH). My boss was concern that since we had a Arc Flash audit and machining had their Category Rating it may change the machine Arc Flash rating.

This long as we match the same fuse rating with the original fuses, shouldn't this be not an issue?

rmonroe

The boss is right. Even replacing a Ferraz A6D fuse with a Ferraz TRS fuse with the same amp rating will affect the arc flash ratings. These are both time delay fuses.

It also depends on whether those fuses being replaced were the one clearing the arc flash fault or not.

Let's say you're talking about a machine panel. If those fuses are the OCPD at the entrance of the panel (fused disconnect or otherwise), then an arc flash study for that panel shouldn't use those as the interrupting OCPD as the fault can be upstream of those fuses but still in the enclosure (ie, on the line side of the fuses).

If the category rating was for a secondary panel/junction box/motor box/etc. of that same machine (where the fuses you want to replace are the main OCPD), then it might affect the category rating as the TCC is most likely not the same.

Yes. Replacing fuses will not affect the arc flash rating of the panel that contains these fuses. It is the downstream panels that can be affected.