I'm building a well house/shop. It is about 150' from where the main
house will be.
It will have a subpanel that will be fed from the main panel at the house.
I will be running 6/3 with ground from the house to the well house.
I have an electrician friend who said the inspector made them install a
main breaker in a subpanel they just did and made them put a hold down
screw in it.

But it is my understanding that you don't need a main breaker if it has 6
or less breakers in the panel. Mine will have just 4.



*You usually don't need a main breaker in a sub-panel if the protection at
the other end is sized properly unless the sub-panel is in a separate
building. Call up the inspector and ask. It is not much of an expense to
install a main breaker and it is not a bad thing to have.

You will need to install at least one ground rod for the well house.