Three phase Kaeser compressor 240 3 phase

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sfork2020

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I am rewiring a Kaeser Compressor The model number is an a S 25 the unit was wired by somebody else not done correctly. Is asking for number 2 AWG WIRE . consumption in amps total 75 then it says pre-fuse amp 110 Amps end it must be dual element time delay fuses. I believe the fuses should be larger I calculated from table 430-52 percentage of full load current75X175= 131.25 next available size would be 150 . any exceptions for 439-52 says dual element fuse shall be permitted to be increased but not more than 225% of the full load motor .Making sure this is correct what I have to use a larger disconnect for those fuses?
 
The fuse requirements for a motor are not a minimum, they are a maximum. Any size fuse equal to or less than the maximum permitted fuse that permits the motor to start is code compliant.
Also note that the percentages used in Table 430.52 are based on the full load currents as found in the tables at the end of Article 430, and not on nameplate current.
 
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sfork2020 said:
Ok so my calculation was wrong?
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He’s not saying that. Just because you calculate (correctly) the max fuse size, you’re not required to use it. You just can’t exceed it.
The manufacturer’s recommendation is likely fine, and is code compliant because it doesn’t exceed the maximum.
 
This kind of sounds like is something that you first apply art 422 then go to art 430 if it directs you there. The instructions of an appliance may very well call for minimum conductor ampacity and specific overcurrent protection.
 
That was from instruction booklet that was in the PDF FILE , 75 was the total Amps for that specific model number witch was a Kaeser
AS25T
 
sfork2020 said:
That was from instruction booklet that was in the PDF FILE , 75 was the total Amps for that specific model number witch was a Kaeser
AS25T
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In general, for the application of 430.52, you use the motor full load currents from Tables 430.247 through 430.250.
 
Jraef said:
Kaeser AS25T is 25HP. In that case the NEC chart says 68A FLC @230V, so MAX fuse is 119A (120), ergo 110A is probably fine.
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And depending on if that machine has other loads besides just the main motor in it might be why OP says it has an input rating of 75.
 
sfork2020 said:
I am rewiring a Kaeser Compressor The model number is an a S 25 the unit was wired by somebody else not done correctly. Is asking for number 2 AWG WIRE . consumption in amps total 75 then it says pre-fuse amp 110 Amps end it must be dual element time delay fuses. I believe the fuses should be larger I calculated from table 430-52 percentage of full load current75X175= 131.25 next available size would be 150 . any exceptions for 439-52 says dual element fuse shall be permitted to be increased but not more than 225% of the full load motor .Making sure this is correct what I have to use a larger disconnect for those fuses?
Click to expand...
For the last 50 years in almost all motors I seldom have a problem if I calculate only going 125 to 135% above motor nameplate ampere and using quality dual element fuses. Back in the 1970's we had trucks where the refrigeration units called for 30 amps. The more expensive Chase Shaumut dual element fuses that appeared to have coated ends were the only fuses that did not occasionally blow in older safety switches. Had air compressors that did not cut off until 150 #'s needed fuses 150 to 175 % higher ampere fuses. Was taught to use the smallest fuse possible. Now with everything.on VFD'S found the drives without a bypass never appeared to need dual element fuses supplying them to be over 125%. Older Danfoss VLT drives with bypasses cut corners by only using a 50 HP contactor on M1 contractors that feed 60 HP Drives. Tech told me that by drives using ramp up times to greatly reduce inrush current they not only need smaller input fuses but a smaller feed contactor. The 60 HP ( M2 ) output contactor that feed motors burnt out ten times more frequently then the undersized 50HP contractors in the over 500 drives we had.
 
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