Breaker size for chiller

[osaengineers]

Hi to All:

Question 1:
My chiller has FLA of 735 of which 718A is the compressor, 6.2A is for oil pump and 10A for controls:
I have calculated my overcurrent protection in the switchgear as follows:
(718x1.75)+6.2+10A=1272.2A. Can I use a 1200A breaker?
Manufacturer says that Maximum over current device is 1600A, but they are putting a 1200A rated non fused disconnect with the equipment.
What would the cable size from the breaker be?. I was going to put 1200A worth of cable.
The next question is: Is the 1200A caculated, should use a 100% rated breaker or not, and what if I used fuses?

Question 2:
There is an existing chiller, that all we know about it is that it is 1040 running amps.

a OCPD for both would be: (1040*1.75)+735=2555AMPS. cAN i USE A 2500A overcurrent device and does it have to be 100% rated

Thanks for the help

 

[bob]

Question 1:
My chiller has FLA of 735 of which 718A is the compressor, 6.2A is for oil pump and 10A for controls:
I have calculated my overcurrent protection in the switchgear as follows:
(718x1.75)+6.2+10A=1272.2A. Can I use a 1200A breaker?
Manufacturer says that Maximum over current device is 1600A, but they are putting a 1200A rated non fused disconnect with the equipment.

The standard OC rating is 175% of the FLA. 440.22 allows you to goto 225% if necessary. 2.25 x 735 = 1653 amps. Maybe the MFG feels the need for the larger breaker. 1.75 x 735 = 1286. You can use the 1200 amp. The question will it allow the starting of the compressor.

What would the cable size from the breaker be?. I was going to put 1200A worth of cable.

The wire size must = to or greater than 1.25 x FLA of the unit. 1.25 x 735 = 919 amps.
3 #350 = 930 amps. 4 # 4/0 = 920 amps. Which would be less expensive?

The next question is: Is the 1200A caculated, should use a 100% rated breaker or not, and what if I used fuses?

Check with the spec on the unit. If the MFG has specified a breaker then you must use a breaker. It does not need to be 100% rated.

Question 2:
There is an existing chiller, that all we know about it is that it is 1040 running amps. a OCPD for both would be: (1040*1.75)+735=2555AMPS. CAN i USE A 2500A overcurrent device and does it have to be 100% rated.

The 2500 amps circuit would be a feeder. The question is will the 2500 amp breaker hold while the smaller unit is running and the larger is starting. You would still have to install overcurrent protection for each unit.