How would you extend underground wire to your panel currently aluminum wire run to panel about 300ft I need to extend this to a new shop with a 100 amp panel 50 extra feet?

Answer 1

This is not a job for an amateur, but I will help you with some primary considerations. My answers are based on the United States' NEC (code) and do not take into consideration any local requirements.

You do not want to extend your existing service conductors. You want to install a 100amp breaker into your existing panel and run conductors from there to your new panel.

If this is a residential application you can run this with #4 copper conductors. If this is a commercial application you must run #3 copper conductors. I would answer this question based on what your shop is intended to do. If you are running professional equipment and are more or less "in business", use the commercial requirements.

If you know how to properly ground a new service, and if your new panel has a main breaker, you can do what you need with 3 conductors. This will allow you to put neutral and ground conductors on the ground bar like you would in your primary panel. If you do not know how to properly ground a new service or doing so is not practical, you will need 4 conductors and your grounds and neutrals will have to be ISOLATED from each other in the new panel. Your neutral bar in this case would be insulated from the panel. In this case your new panel would become a sub-panel of the primary panel.

Some panels do not have a main breaker and this is a critical consideration if you intend to wire it as a new service. Personally, I wouldn't install a panel without a main breaker whether or not it is a service or sub-panel.