On Wed, 09 Nov 2005 17:37:05 GMT, HorneTD
wrote:

Doug Miller wrote:
In article .com, wrote:

#1 is more than NEC calls for. If you have a 200amp panel in the house
and want to run a 100amp sub panel, you will need to run #2AL or #4
Copper.


Ummmm.... this depends a LOT on the specifics of the installation. 100 amps on
#4 copper single insulated conductors in free air is OK, but NOT in raceway or
cable or earth. Ditto #2 aluminum, with the additional caveat that it *also*
depends on the temperature rating of the conductor insulation, e.g. #2
aluminum UF cable is limited to 75A, but #2 aluminum THHN is OK at 100A.



Doug
I'm not trying to quibble when I say that the 90 degree column is useful
only when derating the wire do to the number of conductors in a cable or
raceway or the ambient temperature. Very few terminals are actually
rated at 90 degrees centigrade so your final ampacity is limited to the
ampacity of the conductor at the temperature rating of the terminals to
which it is connected. Since the ampacity of the #2 Al is ninety
amperes at 75 degree centigrade rating of most terminals and that is a
standard breaker and fuse size a larger wire is required.



WOW!

I brought this up to a fellow electrician. Why are we allowed to use
#2 AL for 100amp subpanel, and he said he's used #2 for servers and
feeders for dwellings for years, per Table 310.15(B)(6). I agreed,
and said I wasn't feeding a dewlling, just a sub panel in the same
dwelling, so per 110.14(c)(1) and table 310.16 and limited by 75C
terminals on the sub panel and feeder breaker aren't I limited to 90
amps?

The concensious is #2 AL is good for 100 amps because of Table
310.15(B)(6) reguardless if it's feeding a dewelling or a portion of a
dewelling, it's still a dewelling (loads).

Can anyone confirm this?

later,

tom