Overcurrent Device

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Be_O_Be

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At a code update class an interesting comment with no specific answer:
If the code allows you to go to the next size overcurrent device when the amperage rating of the conductors is such that an overcurrent device (Breaker) does not exist then you are allowed to go to the next closest size. That being said, then if you use 4/0 aluminum and it is rated for 180 amps can you put it on a 200 amp breaker and use it for a 200 amp feed especially the compact aluminum? If so is this more competitive?
 
Be_O_Be said:
At a code update class an interesting comment with no specific answer:
If the code allows you to go to the next size overcurrent device when the amperage rating of the conductors is such that an overcurrent device (Breaker) does not exist then you are allowed to go to the next closest size. That being said, then if you use 4/0 aluminum and it is rated for 180 amps can you put it on a 200 amp breaker and use it for a 200 amp feed especially the compact aluminum? If so is this more competitive?
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The calculated load must be 180 amps or less.

Also, FWIW, under the '08 NEC, SE cable now must be used with the 60 deg column. (150 amps for 4/0 AL)
 
Take a look at the first sentence in 240.4. It says that a conductor must be protected according to it's ampacity listed in 310.15 unless modified by 240.4(A) through (G). The load is limited to the ampacity of the conductor in 310.15. 240.4(B) allows the OCPD to be the next standard size if the ampacity of the conductor isn't a standard size listed in 240.6.
 
Dennis Alwon said:
This is not totally true. If the SE cables is service entrance then, IMO, 4/0 is allowed for 200 amps in dwellings by T. 310.15(B)(6)
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True, but the OP specifically mentioned 4/0 ampacity of 180. That is a 310.16 rating, 4/0 AL @ 75 deg C.

For a residential service, 4/0 AL is good for a full 200 amps
 
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