well, for a 250kcmil has ampacity of 215 amps
two 250 kcmil in parralel have ampacity of 430 amps.
Now, an equivelant area to two 250 kcmils would be a 500kcmil which has a ampacity of 320amps. A 110 amps less than two parralel 250 kcmil. given in same insulation types.
