HVAC breaker, feeder, and 240.4-C

[cyriousn]

We have a chiller that has a MCA of 805A and MOCP of 1200A. A coworker of mine says it's okay to feed the chiller with 2 sets of 600kcmil (840A) as it meets the MCA. Is there an issue with having a 1200A breaker with this feeder size? Does 240.4-C not apply to Chillers under section 440? I feel like I'm missing something here.

 

[infinity]

The MCA can be used to size the conductors. 600 kcmil = 420 amps * 2 = 840 amps so as you have stated the conductor is correctly sized. The OCPD can be 1200 amps as listed on the nameplate.

240.4 Protection of Conductors. Conductors, other than flexible cords, flexible cables, and fixture wires, shall be protected against overcurrent in accordance with their ampacities specified in 310.15, unless otherwise permitted or required in 240.4(A) through (G). Look at T240.4(G).

(G) Overcurrent Protection for Specific Conductor Applications. Overcurrent protection for the specific conductors shall be permitted to be provided as referenced in Table 240.4(G).

 

[texie]

240.4(G) permits this. The next size up rule does not apply here. Your coworker is correct.

 

[infinity]

Look at Table 240.4(G). Also this would be a branch circuit not a feeder.

 

[cyriousn]

Thank you all for the sanity check and the code section references. Just checked the voltage drop and things are looking good!