Exterior breaker panel installation

[pierre]

Re: Exterior breaker panel installation

Ampacity adjustment as per 310.15(B)(2)(a) is required, and it is not occupancy specific.
BUT... for small conductors such as 14, and 12 AWG it is not as big a concern because you are permitted to use the 90 degree column to start your calculations - which in most cases, after adjustment, will not drop the ampacity below 15 amps(14 wire) or 20 amps(12 wire).

[ March 06, 2005, 07:56 AM: Message edited by: pierre ]

 

[jjhoward]

Re: Exterior breaker panel installation

If I do use the 90 degree column from Table 310.16, then I do not need to change the size of the conductors in the conduit. Where is the exception or statement that allows the 90degree column for small conductors?

 

[hurk27]

Re: Exterior breaker panel installation

For NM 334.80

334.80 Ampacity.
The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60?C (140?F) conductor temperature rating. The 90?C (194?F) rating shall be permitted to be used for ampacity derating purposes, provided the final derated ampacity does not exceed that for a 60?C (140?F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.11.

 

[hurk27]

Re: Exterior breaker panel installation

Pierre I can't find where it is allowed to use the 90? column of table 310.16 for derating of conductors in conduit?

 

[pierre]

Re: Exterior breaker panel installation

Read 110.14(C) Temperature Limitations.

Especially the last sentence.

 

[hurk27]

Re: Exterior breaker panel installation

Thank's Pierre I was under the impression that 110.14 was only for the rating and adjustment of conductors for termination purposes? I didn't know it also applied to the derating of conductors in a conduit? And since this would also cover the use of NM conductors why the double wording in 334.80?

 

[pierre]

Re: Exterior breaker panel installation

The wording is included in 334 because if you were to take a peak at the conductors in the NM sheath you will notice there is no marking or identification.
Not only are you permitted to use the 90 degree column for NM ampacity adjustment, but once you complete the calculations, as per 334.80, you will only be permitted to terminate to the 60 degree column ampacity value as per Table 310.16.

 

[jjhoward]

Re: Exterior breaker panel installation

Pierre, thank you for info..Looks like I did not have to change my conductor size for this length of conduit. Now I know for the next time.