RTU Disconnect HP Rating

[xguard]

We are replacing a roof top unit and I want to verify the existing disconnect is correct for the new unit. The existing disconnect is 60A rated for 15 HP with time delay fuses. (NEC references 2014 edition)

RTU information from Manufacturer Cut Sheet:

208-230 VAC, 3 Ph, MCA 49, MCB 60
Compressor 1: 3 Ph / HP 4.8 / Rated Load Amps 19.6 / LRA 136
Compressor 2: 3 Ph / HP 3.7 / Rated Load Amps 13.1 / LRA 83.1
Fan Motor 1: 3 Ph / HP 2.75 / Full Load Amps 7.3 / LRA - not provided
Fan Motor 2: 1 Ph / HP 0.75 / Full Load Amps 3.3 / LRA 12.3

questions

1. The LRA is not provided for fan motor 1. Should I round the hp up to 3 and use table 430.251(B) to select the LRA?

It's looking like my disconnect isn't adequate.

 

[kwired]

I find it a little hard to believe that if max ocp is 60 that a 60 amp disconnect wouldn't be able to handle it. Non fused disconnect often have higher HP rating than fused disconnect of same amp rating, it is the fuse that is the limiting factor in the fused versions.

Example I know I have seen - Square D 600 volt fused disconnect, max HP @ 480 is 15HP. Non fused version has same disconnect mechanism, but max HP rating of 20. This means the switch can handle up to 20 hp, but you generally need more than a 30 amp fuse to allow starting the 20 HP motor and that is the limiting factor on the fused version.

 

[xguard]

I find it a little hard to believe that if max ocp is 60 that a 60 amp disconnect wouldn't be able to handle it. Non fused disconnect often have higher HP rating than fused disconnect of same amp rating, it is the fuse that is the limiting factor in the fused versions.

Example I know I have seen - Square D 600 volt fused disconnect, max HP @ 480 is 15HP. Non fused version has same disconnect mechanism, but max HP rating of 20. This means the switch can handle up to 20 hp, but you generally need more than a 30 amp fuse to allow starting the 20 HP motor and that is the limiting factor on the fused version.

That makes sense to me. Based on the numbers I have now though and the code it looks like I need a 100 amp disconnect with 60 amps fuses, which I agree seems goofy. I'd love for someone to explain it to me.