What gauge of service wire should you run for a 200A service to a meter box and service panel?

Answer for USA, Canada and countries running a 60 Hz supply service.

For a 200 amp service table 310.16 from the NEC is used. This shows that 3/0 cu wire is suitable for 200 amps with an insulation factor of 75 degree C or 210 amps with an insulation factor of 90 degrees C. The neutral may be able do be downsized depending on whether or not harmonic loads exist (i.e. nonlinear loads such as computers). The utility company will run the wire from their transformer to your meter disconnect and meter socket.

Another thought

Be careful. This question can have more than one valid answer. For instance, table 310.16 may apply in some circumstances, but if the 200A service in the question happens to be a single-phase service in a dwelling, there is a different table (310.15(B)(6) just for the purpose of sizing service conductors in that case. It indicates that 2/0 copper OR 4/0 aluminum would be the correct choice.

<><><>

As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

Before you do any work yourself,

on electrical circuits, equipment or appliances,

always use a test meter to ensure the circuit is, in fact, de-energized.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS.