What size of wire is needed for 1500 amps?

There is no single conductor that will handle 1500 amps. For ease of handling, the conductors should be installed in parallel, triple or quad runs.

For a parallel run, 2 - 2000 MCM with an insulation factor of 90 degrees C will give you a total ampacity of 1550 amps.

For a triple run, 3 - 750 MCM with an insulation factor of 90 degrees C will give you a total ampacity of 1500 amps.

For a quad run, 4 - 500 with an insulation factor of 90 degrees C will give you a total ampacity of 1580 amps.