For a 50-amp 220-volt circuit, you would need #6 AWG copper wire. This size is designed to withstand up to 55 amps, so it provides a measure of safety against premature wire failure.
For 30-amp 220-volt circuits, you should use #10 AWG copper wire.
When running wire, it's important to consider the length of the circuit and the current load. Longer runs may require larger wire than what is required for the amperage rating. This is to ensure that the current reaches the end of the circuit without significant loss of voltage.
It is also important to consider the material and gauge of the wire you are using. Copper is the most common material used for electrical wiring, however, other materials such as aluminum can be used as well. The American Wire Gauge (AWG) system is commonly used for marking the wire size and the current capacity of the wire.
For more information about the size of wire and gauges required for different projects, you can refer to the National Electric Code (NEC). This code specifies the type of wiring, materials and gauges that must be used in different applications.
Here is a link to the NEC if you're interested in reading more: https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=70.
You should always consult an electrician when working on electrical projects to ensure that they are done safely and properly.
