Code info sought

[G-ma]

G-ma here
My question pertains to a residential breaker panel upgrade from 100amp to a 200amp service.
The circuitry is aluminum, can I,
1. pigtail copper onto the existing aluminum circuits?
2. If yes, can this be done in the panel or separate junction box?
3. If can be done in the panel, is there a specific method of joining the 2 different wires together, such as a special wire nut?
4. Will the gauge of copper wire be different than the aluminum?

Thank you in advance.

 

[tom baker]

Your questions indicate you are a DIYer. We don’t allow DIY questions as we don’t know what else you are not asking. You are advised to hire an electrical contractor, and ensure permits and inspections are obtained.