100a residential Service

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Hendrix said:
I'm a little confused by 310.15(7). is #1 alum. required for a 100a service riser?
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Assuming you are questioning 310.15 (B)(7).

Next question is which edition of NEC are you using, because 2014 got rid of the table and re-wrote the entire section - but end result is you still have same size conductor in most cases, but they also made it clear that you do apply adjustment factors just like you do for other conductor sizing applications, where earlier editions it did not really make it all that clear if ampacity adjustments were necessary.

Also keep in mind that in order to qualify to be sized per 310.15(B)(7) (regardless of which edition of NEC you are using) the conductor must be supplying the entire load of a one family dwelling unit, or an individual unit of multifamily applications and must be a 120/240 volt single phase supply. It must also be a 100 to 400 amp supply (and the tables in earlier editions do not go beyond 100 to 400 amps).

Without ampacity adjustments being taken into consideration if needed you should be able to use #2 aluminum for a 100 amp application both in 2014 and in prior editions.
 
Look at the example in annex D. I still come up with #2 al. if no other adjustments or corrections are required.

100x.83= 83amps
table 310.15 (B) (16) 75 degree column #2 al.
 
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