Feeder calculation for Chiller

[philly]

I'm coming up with a feeder calculation for a chiller with the following nameplate info and wanted to make sure I was going about it correctly:

Voltage: 480V
Current consumption max: 7.9A
Current consumption compressor/fan/pump: 5.30A / 2x0.80A / 1.00A
Fuse, max: 15.0A
Starting current LRA: 66A

I'm used to chillers providing a minimum circuit ampacity (MCA) and max protective device size. In this case it looks like they are providing the maximum protective device size but do not provide an minimum circuit ampacity.

Looking at 440.33 it looks like the circuit ampacity is determined by taking 125% of the highest motor-compressor current plus the sum the sum of the other loads. So in this case I see this calculation as follows:

Min circuit ampacity = (5.30 * 1.25) + (2*.80) + 1 = 9.22A which can be covered by a #12 AWG. I'm assuming this would be the same value that the manufacture would list as the MCA on the nameplate if it had been listed and saves the extra step of having to carry out this calculation.

For the maximum protection size it looks like 440.22(B)(1) states that overcurrent device must not be large than 225% of highest motor-compressor load plus the current of the other motors. In this case I see this calculation as follows:

Max overcurrent device = (5.30 * 2.25) + (2*.80) + 1 = 14.5A which is very close to the 15A max fuse size listed on the nameplate.

Am I on the right track here?

For load calculation purposes at the panelbaord feeding several of these compressors would I use the 7.90A value for the load calculation. Are there any adjustment factors that are applied to this value when feeding several of these compressors such as using 25% of largest motor like a motor feeder calculation?

 

[Smart $]

I'm coming up with a feeder calculation for a chiller with the following nameplate info and wanted to make sure I was going about it correctly:

Voltage: 480V
Current consumption max: 7.9A
Current consumption compressor/fan/pump: 5.30A / 2x0.80A / 1.00A
Fuse, max: 15.0A
Starting current LRA: 66A

I'm used to chillers providing a minimum circuit ampacity (MCA) and max protective device size. In this case it looks like they are providing the maximum protective device size but do not provide an minimum circuit ampacity.
...

If they are thinking like me, you're going to use 15A fuses and 15A wire (#14 copper)...!!!

 

[philly]

If they are thinking like me, you're going to use 15A fuses and 15A wire (#14 copper)...!!!

Does the feeder size need to have an ampacity equal to or greater than the OCPD? Or since these values are derived separately they do not need to correlate similar to a motor branch circuit not having an ampacity equal to the upstream OCPD? I believe I have seen Chiller feeders previously that do not have the ampacity greater than the upstream OCPD so I assumed that as long as they met the MCA defined on the nameplate that this was ok.

In this situation these units will be fed with 15A breakers instead of fuses. Is this o.k.?

If I'm doing a load calc for a panel and there are several of these units and several other separate motors I'm assuming I use continuous rating of all of these and then just use 125% of either largest single motor or largest compressor motor for the load calc similar to a motor feeder?

 

[Smart $]

Conductors have to be sized for full demand load. Overcurrent devices regarding motors themselves have stipulated maximum ratings but can be less than the required conductor ampacity. However, that would be a highly uncommon scenario because devices with such low rating will typically trip or blow upon energizing the motor circuit. Suffice it to say that minimum circuit ampacity will always be less than maximum OCPD.

If the unit nameplate says "Fuse, maximum" as you wrote above, then you must use fusing for the branch circuit protection.

Code is not uber specific on this but most agree you will satisfy Code if you take 125% of the largest motor (including motor compressor) plus the other motors, plus 125% continuous load plus noncontinuous load. Many just use the MCA value of all units for service and feeder calculations even though that value already includes the extra 25% for the motor compressor.

 

[philly]

Conductors have to be sized for full demand load. Overcurrent devices regarding motors themselves have stipulated maximum ratings but can be less than the required conductor ampacity. However, that would be a highly uncommon scenario because devices with such low rating will typically trip or blow upon energizing the motor circuit. Suffice it to say that minimum circuit ampacity will always be less than maximum OCPD.

So is it possible to have a chiller circuit where the feeder ampacity is less than the overcurrent device based on the individual requirements for each? Or is the minimum circuit ampacity simply a "minimum" required value, but at the end of the day it must have an ampacity equal or greater than the overcurrent device that is required?

If the unit nameplate says "Fuse, maximum" as you wrote above, then you must use fusing for the branch circuit protection.

Out of curiosity why must a fuse be used as opposed to a breaker if the nameplate says "fuse maximum" Is there a reason for using a fuse over a breaker?

Code is not uber specific on this but most agree you will satisfy Code if you take 125% of the largest motor (including motor compressor) plus the other motors, plus 125% continuous load plus noncontinuous load. Many just use the MCA value of all units for service and feeder calculations even though that value already includes the extra 25% for the motor compressor.

So if there is a feeder which feeds two separate chillers with each chiller having a compressor motor and fans then for the feeder calc you would use 125% of the largest compressor motor plus all of the FLA of the other compressor motor and fans on each unit to come up with the feeder size?

What if in the above scenario there are other motors on the feeder that are not part of the chillers? Do you also have to use 125% of the largest "other motor" since these are not part of the chillers?