OCPD Coordination

[mimo]

I ran into this problem, an AC unit is fed from a busduct, the busduct has a fused disconnect switch the fuse rated at 225A type-J, the AC unit is fed thru VFD, a local 200AS/200AF fused disconnect switch (Fuse type-RK5) is located upstream of the VFD, the problem is the 225A fuse by the busduct blow out before the local 200A Fuse, looking at the time current curves that will make sense to happen, I have tried to use get two fuses from the same manufacture but no luck, any other ideas?
Thank you

 

[skeshesh]

That may make sense depending on the time current curves; please provide a link to those if possible. What else is being fed from the busduct? It may be the case that the numbers work out so the fuse protecting the busduct reacts earlier to what happens at the motor considering the additional load on the busduct while the fuse protecting the motor alone only protects the motor. A bit more detail/numbers would help.

 

[mimo]

Only the AC unit is fed from the busduct, the busduct fuse is AMP-TRAP ATJ225, and the local fuse is Bussman FRS-R-200