A 200 amp service needs a wire size of either 2 AWG or kcmil Copper wiring or 4 AWG or kcmil Aluminum or Aluminum clad wiring for the cabling to be installed. The voltage drop and length of the wiring are factors in determining which wire to use. Aluminum wiring demands larger size wires than copper wiring due to its weaker conductivity than copper. https://howtodiscuss.com/t/200-amp-service-wire-size/85876