My question is... how do I figure out what size wire to use when I know the Amperage of the electrical device. Is there some form of electrical calculation?

For example I want to upgrade to a 200 amp panel from a 70 amp panel.

You need to refer to the National Electric Code, Table 310-16, which lists all allowable ampacities of the various sizes and insulations of copper and aluminum wire. Any wire chart you may find elsewhere, such as at a wire manufacturers website, will come directly from this chart.


If the application is residential,smaller wire sizes are allowed, per NEC Table 310.15 B6, which states 200 amp service or feeder can be either # 2/0 copper or 4/0 aluminum.

There are various calculations to arrive at the ampacity of wire,but they are based on many various factors. No need to use the calcs when all have been done and published in the NEC, which, if the installation is in USA, must be followed.

Of course, I am sure you realize the panel, meter, etc, must all be rated for 200 amp also, along with proper grounding of a 200 amp rated service or subpanel. And this installation will need to have the local inspector, and possibly the local utility company involved.

Hope this helps. Let me know if there is any other info you may need.

Tkrussel is correct, wire size comes from a standard table. You can put in a bigger panel making it easier to add circuits and to use the capacity available, but will not be able to use more power than you current service can supply. You may need to talk to your utility company about running heavier service. Unfortunately, to keep rates down, the regulators may not allow the utility the money to upgrade service to older neighborhoods.