What size wire for a 1500 amp service?

Answer 1

There are two main options. A triple run or a quad run in parallel.

For a triple run, a 700 MCM copper conductor with an insulation rating of 90 degrees C is rated at 520 amps.

For a quad run, a 400 MCM copper conductor with an insulation rating of 90 degrees C is rated at 380 amps.

Answer 2

for any span more than 25', #2 gauge; if it is less than 25 feet then consult this table: http://www.rbeelectronics.com/wtable.htm