Commercial 3 phase a/c condenser wiring comes directly off main 3 phase panel without any breaker. This is an old panel that does not have breakers. It only has 1 set of large fuses. This a/c wiring is connected in the main panel after it is fused. It then goes directly from the main panel to a disconnect box on #6. The main and this disconnect are only about 1 foot apart. This disconnect is fused with time delay 60 amp. The load comes off the disconnect on THHN or THWN AWG #8. It runs in conduit about 100 ft to the outside to a non-fused disconnect at the unit.
The condensor has a minimum circuit amp rating of 38.9
What do you think about all of this, especially the #8 carrying the load?
I can't tell how certain things are done but what you mentioned so far sounds OK to me. I understand you have a feeder tap that is about 1 foot long, you did not give all details as to how this tap is connected but sounds like it may be acceptable aside from maybe method of connection - you did not say what size the large fuses are but they can be 10 times the ampacity of the conductor for a tap 10 feet or less - #6 75 degree conductors could be tapped from 650 amp overcurrent device.
You say the unit has a MCA of 38.9 and is fed with #8 THHN/THWN which is good for 40 amps if you have 60 degree terminals or 50 amps if you have 75 degree terminals either way it is more than 38.9 so it is ok.
Marked MCA on these units do not need additional derations because the manufacturer has already included them in the marked values. If you have a high ambient temperature or multiple conductors in the raceway you will need to do these derations to your conductors but not to the MCA.
The 60 amp fuse size will depend on what the unit nameplate calls for overcurrent protection before we determine if it is alright but I am guessing it will be acceptable