Fuses after Circuit Breaker, Coordination

[Wahoo20]

I had a question bothering me. I have a co worker that is putting in line fuses after all of the branch circuit breakers in the panel. His reasoning is that the 3 phase main trips whenever a branch circuit has a overload and not the branch circuit breaker. The main is 100 amp and does not have any adjustment on the trips. This sounds to me that they should remove and replace the breaker. I think they are doing this to save money. It just doesn't sound right to me. Sorry for not having much info.

 

[GoldDigger]

I had a question bothering me. I have a co worker that is putting in line fuses after all of the branch circuit breakers in the panel. His reasoning is that the 3 phase main trips whenever a branch circuit has a overload and not the branch circuit breaker. The main is 100 amp and does not have any adjustment on the trips. This sounds to me that they should remove and replace the breaker. I think they are doing this to save money. It just doesn't sound right to me. Sorry for not having much info.

Are all of the branch circuits single phase?
Or is he assuming that something else will provide phase loss protection if only one of the fuses blows? Or if a fault involves a less than trip current on one phase combined with a tripping current on another?

 

[templdl]

I had a question bothering me. I have a co worker that is putting in line fuses after all of the branch circuit breakers in the panel. His reasoning is that the 3 phase main trips whenever a branch circuit has a overload and not the branch circuit breaker. The main is 100 amp and does not have any adjustment on the trips. This sounds to me that they should remove and replace the breaker. I think they are doing this to save money. It just doesn't sound right to me. Sorry for not having much info.

One thing that has been omitted is as to what trapped the main to begin with. My guess would be a fault in one of the branches. Should there be a fault of a significant magnitude that would fall within the trip range of all breakers in series with the fault it would be a toss up which one would trip. It is no unusual that should there be a bolted fault on a branch circuit that a main will trip an no the branch breaker. The question now is will a fuse blow first? Will a fuse provide better coordination with a bolted fault? Personally it may but I doubt if a fuse would.
Besides that by replacing the breaker I doubt if it's a breaker problem. What is nice about breakers is that they can be tested for calibration which fuses you can not. Why it is assumed that when a fuse has blown that they operated correctly and when a breaker trips it may be considered to be defective if it tripped unreasonably. If a fuse blows more often than not are not questioned. If the fuse is replaced numerous times it is then one looks into what caused the fuse to blow. Plus fuses quite often are not cheep.
She a breaker trips, just latch the beaker and reclose it. If it trips again and again it is easy to blame a defective breaker. As such some consider fuses more credible than breakers.