Short Circuit Protection From Load Side Branch Circuit Fuses

[eurekah]

In a control enclosure we will have a 100A fuse protecting the entire enclosure which is fed into a PDB. The PDB will feed a 60A rated contactor & SSR controlling power to two 28A heater units connected in parallel. Each of the heaters are protected with a 30A fuse block. Will I also require a 60A fuse block before feeding power into the contactor & SSR or will the two 30A fuses on the load side be sufficient?

From my understanding a 60A fuse block protecting the SSR & contactor will be required, but I was wondering if there is an exception if all the devices are located in the same cabinet and load side protection doesn't exceed the rated amperage of the upstream devices.

Thanks for the help. My usual code guru isn't around for a few weeks.

P.S. This is for 480V 3-Ph

 

[Jraef]

It will depend on whether the contactor and SSR have been series rated at your available fault current with a specific fuse that is 60A or higher. I'd say most likely the contactor has, but the SSR is a crap shoot. Some low-end suppliers don't bother. The information is usually in their technical data sheets.